# <a id="monitoring-basics"></a> Monitoring Basics

This part of the Icinga 2 documentation provides an overview of all the basic
monitoring concepts you need to know to run Icinga 2.

## <a id="hosts-services"></a> Hosts and Services

Icinga 2 can be used to monitor the availability of hosts and services. Hosts
and services can be virtually anything which can be checked in some way:

* Network services (HTTP, SMTP, SNMP, SSH, etc.)
* Printers
* Switches / Routers
* Temperature Sensors
* Other local or network-accessible services

Host objects provide a mechanism to group services that are running
on the same physical device.

Here is an example of a host object which defines two child services:

    object Host "my-server1" {
      address = "10.0.0.1"
      check_command = "hostalive"
    }

    object Service "ping4" {
      host_name = "localhost"
      check_command = "ping4"
    }

    object Service "http" {
      host_name = "localhost"
      check_command = "http_ip"
    }

The example creates two services `ping4` and `http` which belong to the
host `my-server1`.

It also specifies that the host should perform its own check using the `hostalive`
check command.

The `address` custom attribute is used by check commands to determine which network
address is associated with the host object.

### <a id="host-states"></a> Host States

Hosts can be in any of the following states:

  Name        | Description
  ------------|--------------
  UP          | The host is available.
  DOWN        | The host is unavailable.

### <a id="service-states"></a> Service States

Services can be in any of the following states:

  Name        | Description
  ------------|--------------
  OK          | The service is working properly.
  WARNING     | The service is experiencing some problems but is still considered to be in working condition.
  CRITICAL    | The service is in a critical state.
  UNKNOWN     | The check could not determine the service's state.

### <a id="hard-soft-states"></a> Hard and Soft States

When detecting a problem with a host/service Icinga re-checks the object a number of
times (based on the `max_check_attempts` and `retry_interval` settings) before sending
notifications. This ensures that no unnecessary notifications are sent for
transient failures. During this time the object is in a `SOFT` state.

After all re-checks have been executed and the object is still in a non-OK
state the host/service switches to a `HARD` state and notifications are sent.

  Name        | Description
  ------------|--------------
  HARD        | The host/service's state hasn't recently changed.
  SOFT        | The host/service has recently changed state and is being re-checked.


## <a id="using-templates"></a> Using Templates

Templates may be used to apply a set of identical attributes to more than one
object:

    template Service "generic-service" {
      max_check_attempts = 3
      check_interval = 5m
      retry_interval = 1m
      enable_perfdata = true
    }

    object Service "ping4" {
      import "generic-service"

      host_name = "localhost"
      check_command = "ping4"
    }

    object Service "ping6" {
      import "generic-service"

      host_name = "localhost"
      check_command = "ping6"
    }

In this example the `ping4` and `ping6` services inherit properties from the
template `generic-service`.

Objects as well as templates themselves can import an arbitrary number of
templates. Attributes inherited from a template can be overridden in the
object if necessary.

## <a id="using-apply"></a> Apply objects based on rules

Instead of assigning each object (`Service`, `Notification`, `Dependency`, `ScheduledDowntime`)
based on attribute identifiers for example `host_name` objects can be [applied](#apply).

    apply Service "ping4" {
      import "generic-service"

      check_command = "ping4"

      assign where "generic-host" in host.templates
      ignore where host.address == ""
    }

In this example the `ping4` service will be created as object for all hosts importing
the `generic-host` template. If the `address` attribute is not set, the host will be
ignored.

## <a id="groups"></a> Groups

Groups are used for combining hosts, services, and users into
accessible configuration attributes and views in external (web)
interfaces.

Group membership is defined at the respective object itself. If
you have a hostgroup name `windows` for example, and want to assign
specific hosts to this group for later viewing the group on your
alert dashboard, first create the hostgroup:

    object HostGroup "windows" {
      display_name = "Windows Servers"
    }

Then add your hosts to this hostgroup

    template Host "windows-server" {
      groups += [ "windows" ]
    }

    object Host "mssql-srv1" {
      import "windows-server"

      vars.mssql_port = 1433
    }

    object Host "mssql-srv2" {
      import "windows-server"

      vars.mssql_port = 1433
    }

This can be done for service and user groups the same way. Additionally
the user groups are associated as attributes in `Notification` objects.

    object UserGroup "windows-mssql-admins" {
      display_name = "Windows MSSQL Admins"
    }

    template User "generic-windows-mssql-users" {
      groups += [ "windows-mssql-admins" ]
    }

    object User "win-mssql-noc" {
      import "generic-windows-mssql-users"

      email = "noc@example.com"
    }

    object User "win-mssql-ops" {
      import "generic-windows-mssql-users"

      email = "ops@example.com"
    }

### <a id="groups"></a> Group Membership Assign

If there is a certain number of hosts, services or users matching a pattern
it's reasonable to assign the group object to these members.
Details on the `assign where` syntax can be found [here]

    object HostGroup "mssql" {
      display_name = "MSSQL Servers"
      assign where host.vars.mssql_port
    }

In this inherited example from above all hosts with the `var` `mssql_port`
set will be added as members to the host group `mssql`.


## <a id="timeperiods"></a> Time Periods

Time Periods define time ranges in Icinga where event actions are
triggered, for example whether a service check is executed or not within
the `check_period` attribute. Or a notification should be sent to
users or not, filtered by the `period` and `notification_period`
configuration attributes for `Notification` and `User` objects.

> **Note**
>
> If you are familar with Icinga 1.x - these time period definitions
> are called `legacy timeperiods` in Icinga 2.
>
> An Icinga 2 legacy timeperiod requires the `ITL` provided template
>`legacy-timeperiod`.

The `TimePeriod` attribute `ranges` may contain multiple directives,
including weekdays, days of the month, and calendar dates.
These types may overlap/override other types in your ranges dictionary.

The descending order of precedence is as follows:

* Calendar date (2008-01-01)
* Specific month date (January 1st)
* Generic month date (Day 15)
* Offset weekday of specific month (2nd Tuesday in December)
* Offset weekday (3rd Monday)
* Normal weekday (Tuesday)

If you don't set any `check_period` or `notification_period` attribute
on your configuration objects Icinga 2 assumes `24x7` as time period
as shown below.

    object TimePeriod "24x7" {
      import "legacy-timeperiod"

      display_name = "Icinga 2 24x7 TimePeriod"
      ranges = {
        "monday"    = "00:00-24:00"
        "tuesday"   = "00:00-24:00"
        "wednesday" = "00:00-24:00"
        "thursday"  = "00:00-24:00"
        "friday"    = "00:00-24:00"
        "saturday"  = "00:00-24:00"
        "sunday"    = "00:00-24:00"
      }
    }

If your operation staff should only be notified during workhours
create a new timeperiod named `workhours` defining a work day from
09:00 to 17:00.

    object TimePeriod "workhours" {
      import "legacy-timeperiod"

      display_name = "Icinga 2 8x5 TimePeriod"
      ranges = {
        "monday"    = "09:00-17:00"
        "tuesday"   = "09:00-17:00"
        "wednesday" = "09:00-17:00"
        "thursday"  = "09:00-17:00"
        "friday"    = "09:00-17:00"
      }
    }

Use the `period` attribute to assign time periods to
`Notification` and `Dependency` objects:

    object Notification "mail" {
      import "generic-notification"

      host_name = "localhost"

      command = "mail-notification"
      users = [ "icingaadmin" ]
      period = "workhours"
    }



## <a id="commands"></a> Commands

Icinga 2 uses three different command object types to specify how
checks should be performed, notifications should be sent and
events should be handled.

### <a id="command-environment-variables"></a> Environment Variables for Commands

Please check [Runtime Custom Attributes as Environment Variables](#runtime-custom-attribute-env-vars).

### <a id="check-commands"></a> Check Commands

`CheckCommand` objects define the command line how a check is called.

`CheckCommand` objects require the [ITL template](#itl-plugin-check-command)
`plugin-check-command` to support native plugin based check methods.

Unless you have done so already, download your check plugin and put it
into the `PluginDir` directory. The following example uses the
`check_disk` plugin shipped with the Monitoring Plugins package.

The plugin path and all command arguments are made a list of
double-quoted string arguments for proper shell escaping.

Call the `check_disk` plugin with the `--help` parameter to see
all available options. Our example defines warning (`-w`) and
critical (`-c`) thresholds for the disk usage. Without any
partition defined (`-p`) it will check all local partitions.

Define the default check command custom attribute `disk_wfree` and `disk_cfree`
freely definable naming schema) and their default threshold values. You can
then use these custom attributes as runtime macros on the command line.

The default custom attributes can be overridden by the custom attributes
defined in the service using the check command `disk`. The custom attributes
can also be inherited from a parent template using additive inheritance (`+=`).

    object CheckCommand "disk" {
      import "plugin-check-command"

      command = [
        PluginDir + "/check_disk",
        "-w", "$disk_wfree$%",
        "-c", "$disk_cfree$%"
      ],

      vars.disk_wfree = 20
      vars.disk_cfree = 10
    }

The host `localhost` with the service `disk` checks all disks with modified
custom attributes (warning thresholds at `10%`, critical thresholds at `5%`
free disk space).

    object Host "localhost" {
      import "generic-host"

      address = "127.0.0.1"
      address6 = "::1"
    }

    object Service "disk" {
      import "generic-service"

      host_name = "localhost"
      check_command = "disk"

      vars.disk_wfree = 10
      vars.disk_cfree = 5
    }


### <a id="notification-commands"></a> Notification Commands

`NotificationCommand` objects define how notifications are delivered to external
interfaces (E-Mail, XMPP, IRC, Twitter, etc).

`NotificationCommand` objects require the [ITL template](#itl-plugin-notification-command)
`plugin-notification-command` to support native plugin-based notifications.

Below is an example using runtime macros from Icinga 2 (such as `$service.output$` for
the current check output) sending an email to the user(s) associated with the
notification itself (`$user.email$`).

If you want to specify default values for some of the custom attribute definitions,
you can add a `vars` dictionary as shown for the `CheckCommand` object.

    object NotificationCommand "mail-service-notification" {
      import "plugin-notification-command"

      command = [ SysconfDir + "/icinga2/scripts/mail-notification.sh" ]

      env = {
        "NOTIFICATIONTYPE" = "$notification.type$"
        "SERVICEDESC" = "$service.name$"
        "HOSTALIAS" = "$host.display_name$",
        "HOSTADDRESS" = "$address$",
        "SERVICESTATE" = "$service.state$",
        "LONGDATETIME" = "$icinga.long_date_time$",
        "SERVICEOUTPUT" = "$service.output$",
        "NOTIFICATIONAUTHORNAME" = "$notification.author$",
        "NOTIFICATIONCOMMENT" = "$notification.comment$",
    	"HOSTDISPLAYNAME" = "$host.display_name$",
        "SERVICEDISPLAYNAME" = "$service.display_name$",
        "USEREMAIL" = "$user.email$"
      }
    }

The command attribute in the `mail-service-notification` command refers to the following
shell script. The macros specified in the `env` array are exported
as environment variables and can be used in the notification script:

    #!/usr/bin/env bash
    template=$(cat <<TEMPLATE
    ***** Icinga  *****

    Notification Type: $NOTIFICATIONTYPE

    Service: $SERVICEDESC
    Host: $HOSTALIAS
    Address: $HOSTADDRESS
    State: $SERVICESTATE

    Date/Time: $LONGDATETIME

    Additional Info: $SERVICEOUTPUT

    Comment: [$NOTIFICATIONAUTHORNAME] $NOTIFICATIONCOMMENT
    TEMPLATE
    )

    /usr/bin/printf "%b" $template | mail -s "$NOTIFICATIONTYPE - $HOSTDISPLAYNAME - $SERVICEDISPLAYNAME is $SERVICESTATE" $USEREMAIL

While it's possible to specify the entire notification command right
in the NotificationCommand object it is generally advisable to create a
shell script in the `/etc/icinga2/scripts` directory and have the
NotificationCommand object refer to that.

### <a id="event-commands"></a> Event Commands

Unlike notifications event commands are called on every service state change
if defined. Therefore the `EventCommand` object should define a command line
evaluating the current service state and other service runtime attributes
available through runtime vars. Runtime macros such as `$SERVICESTATETYPE$`
and `$SERVICESTATE$` will be processed by Icinga 2 helping on fine-granular
events being triggered.

Common use case scenarios are a failing HTTP check requiring an immediate
restart via event command, or if an application is locked and requires
a restart upon detection.

`EventCommand` objects require the ITL template `plugin-event-command`
to support native plugin based checks.

When the event command is triggered on a service state change, it will
send a check result using the `process_check_result` script forcibly
changing the service state back to `OK` (`-r 0`) providing some debug
information in the check output (`-o`).

    object EventCommand "plugin-event-process-check-result" {
      import "plugin-event-command"

      command = [
        PluginDir + "/process_check_result",
        "-H", "$host.name$",
        "-S", "$service.name$",
        "-c", LocalStateDir + "/run/icinga2/cmd/icinga2.cmd",
        "-r", "0",
        "-o", "Event Handler triggered in state '$service.state$' with output '$service.output$'."
      ]
    }

### <a id="commands-arguments"></a> Command Arguments

By defining a check command line using the `command` attribute Icinga 2
will resolve all macros in the static string or array. Sometimes it is
required to extend the arguments list based on a met condition evaluated
at command execution. Or making arguments optional - only set if the
macro value can be resolved by Icinga 2.

    object CheckCommand "check_http" {
      import "plugin-check-command"

      command = PluginDir + "/check_http"

      arguments = {
        "-H" = "$http_vhost$"
        "-I" = "$http_address$"
        "-u" = "$http_uri$"
        "-p" = "$http_port$"
        "-S" = {
          set_if = "$http_ssl$"
        }
        "-w" = "$http_warn_time$"
        "-c" = "$http_critical_time$"
      }

      vars.http_address = "$address$"
      vars.http_ssl = false
    }

The example shows the `check_http` check command defining the most common
arguments. Each of them is optional by default and will be omitted if
the value is not set. For example if the service calling the check command
does not have `vars.http_port` set, it won't get added to the command
line.
If the `vars.http_ssl` custom attribute is set in the service, host or command
object definition, Icinga 2 will add the `-S` argument based on the `set_if`
option to the command line.
That way you can use the `check_http` command definition for both, with and
without SSL enabled checks saving you duplicated command definitions.

Details on all available options can be found in the
[CheckCommand object definition](#objecttype-checkcommand).


## <a id="notifications"></a> Notifications

Notifications for service and host problems are an integral part of your
monitoring setup.

When a host or service is in a downtime, a problem has been acknowledged or
the dependency logic determined that the host/service is unreachable, no
notirications are sent. You can configure additional type and state filters
refining the notifications being actually sent.

There are many ways of sending notifications, e.g. by e-mail, XMPP,
IRC, Twitter, etc. On its own Icinga 2 does not know how to send notifications.
Instead it relies on external mechanisms such as shell scripts to notify users.

A notification specification requires one or more users (and/or user groups)
who will be notified in case of problems. These users must have all custom
attributes defined which will be used in the `NotificationCommand` on execution.

The user `icingaadmin` in the example below will get notified only on `WARNING` and
`CRITICAL` states and `problem` and `recovery` notification types.

    object User "icingaadmin" {
      display_name = "Icinga 2 Admin"
      enable_notifications = true
      states = [ OK, Warning, Critical ]
      types = [ Problem, Recovery ]
      email = "icinga@localhost"
    }

If you don't set the `states` and `types`
configuration attributes for the `User` object, notifications for all states and types
will be sent.

You should choose which information you (and your notified users) are interested in
case of emergency, and also which information does not provide any value to you and
your environment.

An example notification command is explained [here](#notification-commands).

You can add all shared attributes to a `Notification` template which is inherited
to the defined notifications. That way you'll save duplicated attributes in each
`Notification` object. Attributes can be overridden locally.


    template Notification "generic-notification" {
      interval = 15m

      command = "mail-service-notification"

      states = [ Warning, Critical, Unknown ]
      types = [ Problem, Acknowledgement, Recovery, Custom, FlappingStart,
                FlappingEnd, DowntimeStart,DowntimeEnd, DowntimeRemoved ]

      period = "24x7"
    }

The time period `24x7` is shipped as example configuration with Icinga 2.

Use the `apply` keyword to create `Notification` objects for your services:

    apply Notification "mail" to Service {
      import "generic-notification"

      command = "mail-notification"
      users = [ "icingaadmin" ]

      assign where service.name == "mysql"
    }

Instead of assigning users to notifications, you can also add the `user_groups`
attribute with a list of user groups to the `Notification` object. Icinga 2 will
send notifications to all group members.

### <a id="notification-escalations"></a> Notification Escalations

When a problem notification is sent and a problem still exists after re-notification
you may want to escalate the problem to the next support level. A different approach
is to configure the default notification by email, and escalate the problem via sms
if not already solved.

You can define notification start and end times as additional configuration
attributes making the `Notification` object a so-called `notification escalation`.
Using templates you can share the basic notification attributes such as users or the
`interval` (and override them for the escalation then).

Using the example from above, you can define additional users being escalated for sms
notifications between start and end time.

    object User "icinga-oncall-2nd-level" {
      display_name = "Icinga 2nd Level"

      vars.mobile = "+1 555 424642"
    }

    object User "icinga-oncall-1st-level" {
      display_name = "Icinga 1st Level"

      vars.mobile = "+1 555 424642"
    }

Define an additional `NotificationCommand` for SMS notifications.

> **Note**
>
> The example is not complete as there are many different SMS providers.
> Please note that sending SMS notifications will require an SMS provider
> or local hardware with a SIM card active.

    object NotificationCommand "sms-notification" {
       command = [
         PluginDir + "/send_sms_notification",
         "$mobile$",
         "..."
    }

The two new notification escalations are added onto the host `localhost`
and its service `ping4` using the `generic-notification` template.
The user `icinga-oncall-2nd-level` will get notified by SMS (`sms-notification`
command) after `30m` until `1h`.

> **Note**
>
> The `interval` was set to 15m in the `generic-notification`
> template example. Lower that value in your escalations by using a secondary
> template or overriding the attribute directly in the `notifications` array
> position for `escalation-sms-2nd-level`.

If the problem does not get resolved or acknowledged preventing further notifications
the `escalation-sms-1st-level` user will be escalated `1h` after the initial problem was
notified, but only for one hour (`2h` as `end` key for the `times` dictionary).

    apply Notification "mail" to Service {
      import "generic-notification"

      command = "mail-notification"
      users = [ "icingaadmin" ]

      assign where service.name == "ping4"
    }

    apply Notification "escalation-sms-2nd-level" to Service {
      import "generic-notification"

      command = "sms-notification"
      users = [ "icinga-oncall-2nd-level" ]

      times = {
        begin = 30m
        end = 1h
      }

      assign where service.name == "ping4"
    }

    apply Notification "escalation-sms-1st-level" to Service {
      import "generic-notification"

      command = "sms-notification"
      users = [ "icinga-oncall-1st-level" ]

      times = {
        begin = 1h
        end = 2h
      }

      assign where service.name == "ping4"
    }

### <a id="first-notification-delay"></a> First Notification Delay

Sometimes the problem in question should not be notified when the first notification
happens, but a defined time duration afterwards. In Icinga 2 you can use the `times`
dictionary and set `begin = 15m` as key and value if you want to suppress notifications
in the first 15 minutes. Leave out the `end` key - if not set, Icinga 2 will not check against any
end time for this notification.

    apply Notification "mail" to Service {
      import "generic-notification"

      command = "mail-notification"
      users = [ "icingaadmin" ]

      times.begin = 15m // delay first notification

      assign where service.name == "ping4"
    }

### <a id="notification-filters-state-type"></a> Notification Filters by State and Type

If there are no notification state and type filter attributes defined at the `Notification`
or `User` object Icinga 2 assumes that all states and types are being notified.

Available state and type filters for notifications are:

    template Notification "generic-notification" {

      states = [ Warning, Critical, Unknown ]
      types = [ Problem, Acknowledgement, Recovery, Custom, FlappingStart,
                FlappingEnd, DowntimeStart, DowntimeEnd, DowntimeRemoved ]
    }

If you are familiar with Icinga 1.x `notification_options` please note that they have been split
into type and state, and allow more fine granular filtering for example on downtimes and flapping.
You can filter for acknowledgements and custom notifications too.


## <a id="downtimes"></a> Downtimes

Downtimes can be scheduled for planned server maintenance or
any other targetted service outage you are aware of in advance.

Downtimes will suppress any notifications, and may trigger other
downtimes too. If the downtime was set by accident, or the duration
exceeds the maintenance, you can manually cancel the downtime.
Planned downtimes will also be taken into account for SLA reporting
tools calculating the SLAs based on the state and downtime history.

Downtimes may overlap with their start and end times. If there
are multiple downtimes triggered for one object, the overall downtime depth
will be more than `1`. This is useful when you want to extend
your maintenance window taking longer than expected.

### <a id="fixed-flexible-downtimes"></a> Fixed and Flexible Downtimes

A `fixed` downtime will be activated at the defined start time, and
removed at the end time. During this time window the service state
will change to `NOT-OK` and then actually trigger the downtime.
Notifications are suppressed and the downtime depth is incremented.

Common scenarios are a planned distribution upgrade on your linux
servers, or database updates in your warehouse. The customer knows
about a fixed downtime window between 23:00 and 24:00. After 24:00
all problems should be alerted again. Solution is simple -
schedule a `fixed` downtime starting at 23:00 and ending at 24:00.

Unlike a `fixed` downtime, a `flexible` downtime end does not necessarily
happen at the provided end time. Instead the downtime will be triggered
by the state change in the time span defined by start and end time, but
then last a defined duration in minutes.

Imagine the following scenario: Your service is frequently polled
by users trying to grab free deleted domains for immediate registration.
Between 07:30 and 08:00 the impact will hit for 15 minutes and generate
a network outage visible to the monitoring. The service is still alive,
but answering too slow to Icinga 2 service checks.
For that reason, you may want to schedule a downtime between 07:30 and
08:00 with a duration of 15 minutes. The downtime will then last from
its trigger time until the duration is over. After that, the downtime
is removed (may happen before or after the actual end time!).

### <a id="scheduling-downtime"></a> Scheduling a downtime

This can either happen through a web interface or by sending an [external command](#external-commands)
to the external command pipe provided by the `ExternalCommandListener` configuration.

Fixed downtimes require a start and end time (a duration will be ignored).
Flexible downtimes need a start and end time for the time span, and a duration
independent from that time span.

### <a id="triggered-downtimes"></a> Triggered Downtimes

This is optional when scheduling a downtime. If there is already a downtime
scheduled for a future maintenance, the current downtime can be triggered by
that downtime. This renders useful if you have scheduled a host downtime and
are now scheduling a child host's downtime getting triggered by the parent
downtime on NOT-OK state change.

### <a id="recurring-downtimes"></a> Recurring Downtimes

[ScheduledDowntime objects](#objecttype-scheduleddowntime) can be used to set up
recurring downtimes for services.

Example:

    apply ScheduledDowntime "backup-downtime" to Service {
      author = "icingaadmin"
      comment = "Scheduled downtime for backup"

      ranges = {
        monday = "02:00-03:00"
        tuesday = "02:00-03:00"
        wednesday = "02:00-03:00"
        thursday = "02:00-03:00"
        friday = "02:00-03:00"
        saturday = "02:00-03:00"
        sunday = "02:00-03:00"
      }

      assign where "backup" in service.groups
    }


## <a id="comments"></a> Comments

Comments can be added at runtime and are persistent over restarts. You can
add useful information for others on repeating incidents (for example
"last time syslog at 100% cpu on 17.10.2013 due to stale nfs mount") which
is primarly accessible using web interfaces.

Adding and deleting comment actions are possible through the external command pipe
provided with the `ExternalCommandListener` configuration. The caller must
pass the comment id in case of manipulating an existing comment.


## <a id="acknowledgements"></a> Acknowledgements

If a problem is alerted and notified you may signal the other notification
receipients that you are aware of the problem and will handle it.

By sending an acknowledgement to Icinga 2 (using the external command pipe
provided with `ExternalCommandListener` configuration) all future notifications
are suppressed, a new comment is added with the provided description and
a notification with the type `NotificationFilterAcknowledgement` is sent
to all notified users.

### <a id="expiring-acknowledgements"></a> Expiring Acknowledgements

Once a problem is acknowledged it may disappear from your `handled problems`
dashboard and no-one ever looks at it again since it will suppress
notifications too.

This `fire-and-forget` action is quite common. If you're sure that a
current problem should be resolved in the future at a defined time,
you can define an expiration time when acknowledging the problem.

Icinga 2 will clear the acknowledgement when expired and start to
re-notify if the problem persists.


## <a id="dependencies"></a> Dependencies

Icinga 2 uses host and service [Dependency](#objecttype-dependency) objects
for determing their network reachability.
The `parent_host_name` and `parent_service_name` attributes are mandatory for
service dependencies, `parent_host_name` is required for host dependencies.

A service can depend on a host, and vice versa. A service has an implicit
dependency (parent) to its host. A host to host dependency acts implicit
as host parent relation.
When dependencies are calculated, not only the immediate parent is taken into
account but all parents are inherited.

Notifications are suppressed if a host or service becomes unreachable.

A common scenario is the Icinga 2 server behind a router. Checking internet
access by pinging the Google DNS server `google-dns` is a common method, but
will fail in case the `dsl-router` host is down. Therefore the example below
defines a host dependency which acts implicit as parent relation too.

Furthermore the host may be reachable but ping probes are dropped by the
router's firewall. In case the `dsl-router``ping4` service check fails, all
further checks for the `ping4` service on host `google-dns` service should
be suppressed. This is achieved by setting the `disable_checks` attribute to `true`.

    object Host "dsl-router" {
      address = "192.168.1.1"
    }

    object Host "google-dns" {
      address = "8.8.8.8"
    }

    apply Service "ping4" {
      import "generic-service"

      check_command = "ping4"

      assign where host.address
    }

    apply Dependency "internet" to Service {
      parent_host_name = "dsl-router"
      disable_checks = true

      assign where host.name != "dsl-router"
    }


## <a id="custom-attributes"></a> Custom Attributes

### <a id="runtime-custom-attributes"></a> Using Custom Attributes at Runtime

Custom attributes may be used in command definitions to dynamically change how the command
is executed.

Additionally there are Icinga 2 features such as the `PerfDataWriter` type
which use custom attributes to format their output.

> **Tip**
>
> Custom attributes are identified by the 'vars' dictionary attribute as short name.
> Accessing the different attribute keys is possible using the '.' accessor.

Custom attributes in command definitions or performance data templates are evaluated at
runtime when executing a command. These custom attributes cannot be used elsewhere
(e.g. in other configuration attributes).

Here is an example of a command definition which uses user-defined custom attributes:

    object CheckCommand "my-ping" {
      import "plugin-check-command"

      command = [
        PluginDir + "/check_ping",
        "-4",
        "-H", "$address$",
        "-w", "$ping_wrta$,$ping_wpl$%",
        "-c", "$ping_crta$,$ping_cpl$%",
        "-p", "$ping_packets$",
        "-t", "$ping_timeout$"
      ]

      vars.ping_wrta = 100
      vars.ping_wpl = 5
      vars.ping_crta = 200
      vars.ping_cpl = 15
      vars.ping_packets = 5
      vars.ping_timeout = 0
    }

Custom attribute names used at runtime must be enclosed in two `$` signs, e.g.
`$address$`. When using the `$` sign as single character, you need to escape
it with an additional dollar sign (`$$`).

### <a id="runtime-custom-attributes-evaluation-order"></a> Runtime Custom Attributes Evaluation Order

When executing commands Icinga 2 checks the following objects in this order to look
up custom attributes and their respective values:

1. User object (only for notifications)
2. Service object
3. Host object
4. Command object
5. Global custom attributes in the Vars constant

This execution order allows you to define default values for custom attributes
in your command objects. The `my-ping` command shown above uses this to set
default values for some of the latency thresholds and timeouts.

When using the `my-ping` command you can override all or some of the custom
attributes in the service definition like this:

    object Service "ping" {
      host_name = "localhost"
      check_command = "my-ping"

      vars.ping_packets = 10 // Overrides the default value of 5 given in the command
    }

If a custom attribute isn't defined anywhere an empty value is used and a warning is
emitted to the Icinga 2 log.

> **Best Practice**
>
> By convention every host should have an `address` attribute. Hosts
> which have an IPv6 address should also have an `address6` attribute.

### <a id="runtime-custom-attribute-env-vars"></a> Runtime Custom Attributes as Environment Variables

The `env` command object attribute specifies a list of environment variables with values calculated
from either runtime macros or custom attributes which should be exported as environment variables
prior to executing the command.

This is useful for example for hiding sensitive information on the command line output
when passing credentials to database checks:

    object CheckCommand "mysql-health" {
      import "plugin-check-command",

      command = PluginDir + "/check_mysql -H $address$ -d $db$",

      vars.mysql_user = "icinga_check",
      vars.mysql_pass = "password"

      env.MYSQLUSER = "$mysql_user$",
      env.MYSQLPASS = "$mysql_pass$"
    }

### <a id="modified-attributes"></a> Modified Attributes

Icinga 2 allows you to modify defined object attributes at runtime different to
the local configuration object attributes. These modified attributes are
stored as bit-shifted-value and made available in backends. Icinga 2 stores
modified attributes in its state file and restores them on restart.

Modified Attributes can be reset using external commands.


## <a id="runtime-macros"></a> Runtime Macros

Next to custom attributes there are additional runtime macros made available by Icinga 2.
These runtime macros reflect the current object state and may change over time while
custom attributes are configured statically (but can be modified at runtime using
external commands).

### <a id="runtime-macro-evaluation-order"></a> Runtime Macro Evaluation Order

Custom attributes can be accessed at [runtime](#runtime-custom-attributes) using their
identifier omitting the `vars.` prefix.
There are special cases when those custom attributes are not set and Icinga 2 provides
a fallback to existing object attributes for example `host.address`.

In the following example the `$address$` macro will be resolved with the value of `vars.address`.

    object Host "localhost" {
      import "generic-host"
      check_command = "my-host-macro-test"
      address = "127.0.0.1"
      vars.address = "127.2.2.2"
    }

    object CheckCommand "my-host-macro-test" {
      command = "echo \"address: $address$ host.address: $host.address$ host.vars.address: $host.vars.address$\""
    }

The check command output will look like

    "address: 127.2.2.2 host.address: 127.0.0.1 host.vars.address: 127.2.2.2"

If you alter the host object and remove the `vars.address` line, Icinga 2 will fail to look up `$address$` in the
custom attributes dictionary and then look for the host object's attribute.

The check command output will change to

    "address: 127.0.0.1 host.address: 127.0.0.1 host.vars.address: "


The same example can be defined for services overriding the `address` field based on a specific host custom attribute.

    object Host "localhost" {
      import "generic-host"
      address = "127.0.0.1"
      vars.macro_address = "127.3.3.3"
    }

    apply Service "my-macro-test" to Host {
      import "generic-service"
      check_command = "my-service-macro-test"
      vars.address = "$host.vars.macro_address$"

      assign where host.address
    }

    object CheckCommand "my-service-macro-test" {
      command = "echo \"address: $address$ host.address: $host.address$ host.vars.macro_address: $host.vars.macro_address$ service.vars.address: $service.vars.address$\""
    }

When the service check is executed the output looks like

    "address: 127.3.3.3 host.address: 127.0.0.1 host.vars.macro_address: 127.3.3.3 service.vars.address: 127.3.3.3"

That way you can easily override existing macros being accessed by their short name like `$address$` and refrain
from defining multiple check commands (one for `$address$` and one for `$host.vars.macro_address$`).


### <a id="host-runtime-macros"></a> Host Runtime Macros

The following host custom attributes are available in all commands that are executed for
hosts or services:

  Name                         | Description
  -----------------------------|--------------
  host.name                    | The name of the host object.
  host.display_name            | The value of the `display_name` attribute.
  host.state                   | The host's current state. Can be one of `UNREACHABLE`, `UP` and `DOWN`.
  host.state_id                | The host's current state. Can be one of `0` (up), `1` (down) and `2` (unreachable).
  host.state_type              | The host's current state type. Can be one of `SOFT` and `HARD`.
  host.check_attempt           | The current check attempt number.
  host.max_check_attempts      | The maximum number of checks which are executed before changing to a hard state.
  host.last_state              | The host's previous state. Can be one of `UNREACHABLE`, `UP` and `DOWN`.
  host.last_state_id           | The host's previous state. Can be one of `0` (up), `1` (down) and `2` (unreachable).
  host.last_state_type         | The host's previous state type. Can be one of `SOFT` and `HARD`.
  host.last_state_change       | The last state change's timestamp.
  host.duration_sec            | The time since the last state change.
  host.latency                 | The host's check latency.
  host.execution_time          | The host's check execution time.
  host.output                  | The last check's output.
  host.perfdata                | The last check's performance data.
  host.last_check              | The timestamp when the last check was executed.
  host.num_services            | Number of services associated with the host.
  host.num_services_ok         | Number of services associated with the host which are in an `OK` state.
  host.num_services_warning    | Number of services associated with the host which are in a `WARNING` state.
  host.num_services_unknown    | Number of services associated with the host which are in an `UNKNOWN` state.
  host.num_services_critical   | Number of services associated with the host which are in a `CRITICAL` state.

### <a id="service-runtime-macros"></a> Service Runtime Macros

The following service macros are available in all commands that are executed for
services:

  Name                       | Description
  ---------------------------|--------------
  service.name               | The short name of the service object.
  service.display_name       | The value of the `display_name` attribute.
  service.check_command      | The short name of the command along with any arguments to be used for the check.
  service.state              | The service's current state. Can be one of `OK`, `WARNING`, `CRITICAL` and `UNKNOWN`.
  service.state_id           | The service's current state. Can be one of `0` (ok), `1` (warning), `2` (critical) and `3` (unknown).
  service.state_type         | The service's current state type. Can be one of `SOFT` and `HARD`.
  service.check_attempt      | The current check attempt number.
  service.max_check_attempts | The maximum number of checks which are executed before changing to a hard state.
  service.last_state         | The service's previous state. Can be one of `OK`, `WARNING`, `CRITICAL` and `UNKNOWN`.
  service.last_state_id      | The service's previous state. Can be one of `0` (ok), `1` (warning), `2` (critical) and `3` (unknown).
  service.last_state_type    | The service's previous state type. Can be one of `SOFT` and `HARD`.
  service.last_state_change  | The last state change's timestamp.
  service.duration_sec       | The time since the last state change.
  service.latency            | The service's check latency.
  service.execution_time     | The service's check execution time.
  service.output             | The last check's output.
  service.perfdata           | The last check's performance data.
  service.last_check         | The timestamp when the last check was executed.

### <a id="command-runtime-macros"></a> Command Runtime Macros

The following custom attributes are available in all commands:

  Name                   | Description
  -----------------------|--------------
  command.name           | The name of the command object.

### <a id="user-runtime-macros"></a> User Runtime Macros

The following custom attributes are available in all commands that are executed for
users:

  Name                   | Description
  -----------------------|--------------
  user.name              | The name of the user object.
  user.display_name      | The value of the display_name attribute.

### <a id="notification-runtime-macros"></a> Notification Runtime Macros

  Name                   | Description
  -----------------------|--------------
  notification.type      | The type of the notification.
  notification.author    | The author of the notification comment, if existing.
  notification.comment   | The comment of the notification, if existing.

### <a id="global-runtime-macros"></a> Global Runtime Macros

The following macros are available in all executed commands:

  Name                   | Description
  -----------------------|--------------
  icinga.timet           | Current UNIX timestamp.
  icinga.long_date_time  | Current date and time including timezone information. Example: `2014-01-03 11:23:08 +0000`
  icinga.short_date_time | Current date and time. Example: `2014-01-03 11:23:08`
  icinga.date            | Current date. Example: `2014-01-03`
  icinga.time            | Current time including timezone information. Example: `11:23:08 +0000`
  icinga.uptime          | Current uptime of the Icinga 2 process.

The following macros provide global statistics:

  Name                              | Description
  ----------------------------------|--------------
  icinga.num_services_ok            | Current number of services in state 'OK'.
  icinga.num_services_warning       | Current number of services in state 'Warning'.
  icinga.num_services_critical      | Current number of services in state 'Critical'.
  icinga.num_services_unknown       | Current number of services in state 'Unknown'.
  icinga.num_services_pending       | Current number of pending services.
  icinga.num_services_unreachable   | Current number of unreachable services.
  icinga.num_services_flapping      | Current number of flapping services.
  icinga.num_services_in_downtime   | Current number of services in downtime.
  icinga.num_services_acknowledged  | Current number of acknowledged service problems.
  icinga.num_hosts_up               | Current number of hosts in state 'Up'.
  icinga.num_hosts_down             | Current number of hosts in state 'Down'.
  icinga.num_hosts_unreachable      | Current number of unreachable hosts.
  icinga.num_hosts_flapping         | Current number of flapping hosts.
  icinga.num_hosts_in_downtime      | Current number of hosts in downtime.
  icinga.num_hosts_acknowledged     | Current number of acknowledged host problems.


## <a id="check-result-freshness"></a> Check Result Freshness

In Icinga 2 active check freshness is enabled by default. It is determined by the
`check_interval` attribute and no incoming check results in that period of time.

    threshold = last check execution time + check interval

Passive check freshness is calculated from the `check_interval` attribute if set.

    threshold = last check result time + check interval

If the freshness checks are invalid, a new check is executed defined by the
`check_command` attribute.


## <a id="check-flapping"></a> Check Flapping

The flapping algorithm used in Icinga 2 does not store the past states but
calculcates the flapping threshold from a single value based on counters and
half-life values. Icinga 2 compares the value with a single flapping threshold
configuration attribute named `flapping_threshold`.

Flapping detection can be enabled or disabled using the `enable_flapping` attribute.


## <a id="volatile-services"></a> Volatile Services

By default all services remain in a non-volatile state. When a problem
occurs, the `SOFT` state applies and once `max_check_attempts` attribute
is reached with the check counter, a `HARD` state transition happens.
Notifications are only triggered by `HARD` state changes and are then
re-sent defined by the `interval` attribute.

It may be reasonable to have a volatile service which stays in a `HARD`
state type if the service stays in a `NOT-OK` state. That way each
service recheck will automatically trigger a notification unless the
service is acknowledged or in a scheduled downtime.


## <a id="external-commands"></a> External Commands

Icinga 2 provides an external command pipe for processing commands
triggering specific actions (for example rescheduling a service check
through the web interface).

In order to enable the `ExternalCommandListener` configuration use the
following command and restart Icinga 2 afterwards:

    # icinga2-enable-feature command

Icinga 2 creates the command pipe file as `/var/run/icinga2/cmd/icinga2.cmd`
using the default configuration.

Web interfaces and other Icinga addons are able to send commands to
Icinga 2 through the external command pipe, for example for rescheduling
a forced service check:

    # /bin/echo "[`date +%s`] SCHEDULE_FORCED_SVC_CHECK;localhost;ping4;`date +%s`" >> /var/run/icinga2/cmd/icinga2.cmd

    # tail -f /var/log/messages

    Oct 17 15:01:25 icinga-server icinga2: Executing external command: [1382014885] SCHEDULE_FORCED_SVC_CHECK;localhost;ping4;1382014885
    Oct 17 15:01:25 icinga-server icinga2: Rescheduling next check for service 'ping4'

By default the command pipe file is owned by the group `icingacmd` with read/write
permissions. Add your webserver's user to the group `icingacmd` to
enable sending commands to Icinga 2 through your web interface:

    # usermod -G -a icingacmd www-data

Debian packages use `nagios` as the default user and group name. Therefore change `icingacmd` to
`nagios`.

### <a id="external-command-list"></a> External Command List

A list of currently supported external commands can be found [here](#external-commands-list-detail)

Detailed information on the commands and their required parameters can be found
on the [Icinga 1.x documentation](http://docs.icinga.org/latest/en/extcommands2.html).


## <a id="event-handlers"></a> Event Handlers

Event handlers are defined as `EventCommand` objects in Icinga 2.

Unlike notifications event commands are called on every host/service execution
if defined. Therefore the `EventCommand` object should define a command line
evaluating the current service state and other service runtime attributes
available through runtime macros. Runtime macros such as `$service.state_type$`
and `$service.state$` will be processed by Icinga 2 helping on fine-granular
events being triggered.

Common use case scenarios are a failing HTTP check requiring an immediate
restart via event command, or if an application is locked and requires
a restart upon detection.


## <a id="logging"></a> Logging

Icinga 2 supports three different types of logging:

* File logging
* Syslog (on *NIX-based operating systems)
* Console logging (`STDOUT` on tty)

You can enable additional loggers using the `icinga2-enable-feature`
and `icinga2-disable-feature` commands to configure loggers:

Feature  | Description
---------|------------
debuglog | Debug log (path: `/var/log/icinga2/debug.log`, severity: `debug` or higher)
mainlog  | Main log (path: `/var/log/icinga2/icinga2.log`, severity: `information` or higher)
syslog   | Syslog (severity: `warning` or higher)

By default file the `mainlog` feature is enabled. When running Icinga 2
on a terminal log messages with severity `information` or higher are
written to the console.


## <a id="performance-data"></a> Performance Data

When a host or service check is executed plugins should provide so-called
`performance data`. Next to that additional check performance data
can be fetched using Icinga 2 runtime macros such as the check latency
or the current service state (or additional custom attributes).

The performance data can be passed to external applications which aggregate and
store them in their backends. These tools usually generate graphs for historical
reporting and trending.

Well-known addons processing Icinga performance data are PNP4Nagios,
inGraph and Graphite.

### <a id="writing-performance-data-files"></a> Writing Performance Data Files

PNP4Nagios, inGraph and Graphios use performance data collector daemons to fetch
the current performance files for their backend updates.

Therefore the Icinga 2 `PerfdataWriter` object allows you to define
the output template format for host and services backed with Icinga 2
runtime vars.

    host_format_template = "DATATYPE::HOSTPERFDATA\tTIMET::$icinga.timet$\tHOSTNAME::$host.name$\tHOSTPERFDATA::$host.perfdata$\tHOSTCHECKCOMMAND::$host.checkcommand$\tHOSTSTATE::$host.state$\tHOSTSTATETYPE::$host.statetype$"
    service_format_template = "DATATYPE::SERVICEPERFDATA\tTIMET::$icinga.timet$\tHOSTNAME::$host.name$\tSERVICEDESC::$service.description$\tSERVICEPERFDATA::$service.perfdata$\tSERVICECHECKCOMMAND::$service.checkcommand$\tHOSTSTATE::$host.state$\tHOSTSTATETYPE::$host.statetype$\tSERVICESTATE::$service.state$\tSERVICESTATETYPE::$service.statetype$"

The default templates are already provided with the Icinga 2 feature configuration
which can be enabled using

    # icinga2-enable-feature perfdata

By default all performance data files are rotated in a 15 seconds interval into
the `/var/spool/icinga2/perfdata/` directory as `host-perfdata.<timestamp>` and
`service-perfdata.<timestamp>`.
External collectors need to parse the rotated performance data files and then
remove the processed files.

### <a id="graphite-carbon-cache-writer"></a> Graphite Carbon Cache Writer

While there are some Graphite collector scripts and daemons like Graphios available for
Icinga 1.x it's more reasonable to directly process the check and plugin performance
in memory in Icinga 2. Once there are new metrics available, Icinga 2 will directly
write them to the defined Graphite Carbon daemon tcp socket.

You can enable the feature using

    # icinga2-enable-feature graphite

By default the `GraphiteWriter` object expects the Graphite Carbon Cache to listen at
`127.0.0.1` on port `2003`.

The current naming schema is

    icinga.<hostname>.<metricname>
    icinga.<hostname>.<servicename>.<metricname>



## <a id="status-data"></a> Status Data

Icinga 1.x writes object configuration data and status data in a cyclic
interval to its `objects.cache` and `status.dat` files. Icinga 2 provides
the `StatusDataWriter` object which dumps all configuration objects and
status updates in a regular interval.

    # icinga2-enable-feature statusdata

Icinga 1.x Classic UI requires this data set as part of its backend.

> **Note**
>
> If you are not using any web interface or addon which uses these files
> you can safely disable this feature.



## <a id="compat-logging"></a> Compat Logging

The Icinga 1.x log format is considered being the `Compat Log`
in Icinga 2 provided with the `CompatLogger` object.

These logs are not only used for informational representation in
external web interfaces parsing the logs, but also to generate
SLA reports and trends in Icinga 1.x Classic UI. Futhermore the
`Livestatus` feature uses these logs for answering queries to
historical tables.

The `CompatLogger` object can be enabled with

    # icinga2-enable-feature compatlog

By default, the Icinga 1.x log file called `icinga.log` is located
in `/var/log/icinga2/compat`. Rotated log files are moved into
`var/log/icinga2/compat/archives`.

The format cannot be changed without breaking compatibility to
existing log parsers.

    # tail -f /var/log/icinga2/compat/icinga.log

    [1382115688] LOG ROTATION: HOURLY
    [1382115688] LOG VERSION: 2.0
    [1382115688] HOST STATE: CURRENT;localhost;UP;HARD;1;
    [1382115688] SERVICE STATE: CURRENT;localhost;disk;WARNING;HARD;1;
    [1382115688] SERVICE STATE: CURRENT;localhost;http;OK;HARD;1;
    [1382115688] SERVICE STATE: CURRENT;localhost;load;OK;HARD;1;
    [1382115688] SERVICE STATE: CURRENT;localhost;ping4;OK;HARD;1;
    [1382115688] SERVICE STATE: CURRENT;localhost;ping6;OK;HARD;1;
    [1382115688] SERVICE STATE: CURRENT;localhost;processes;WARNING;HARD;1;
    [1382115688] SERVICE STATE: CURRENT;localhost;ssh;OK;HARD;1;
    [1382115688] SERVICE STATE: CURRENT;localhost;users;OK;HARD;1;
    [1382115706] EXTERNAL COMMAND: SCHEDULE_FORCED_SVC_CHECK;localhost;disk;1382115705
    [1382115706] EXTERNAL COMMAND: SCHEDULE_FORCED_SVC_CHECK;localhost;http;1382115705
    [1382115706] EXTERNAL COMMAND: SCHEDULE_FORCED_SVC_CHECK;localhost;load;1382115705
    [1382115706] EXTERNAL COMMAND: SCHEDULE_FORCED_SVC_CHECK;localhost;ping4;1382115705
    [1382115706] EXTERNAL COMMAND: SCHEDULE_FORCED_SVC_CHECK;localhost;ping6;1382115705
    [1382115706] EXTERNAL COMMAND: SCHEDULE_FORCED_SVC_CHECK;localhost;processes;1382115705
    [1382115706] EXTERNAL COMMAND: SCHEDULE_FORCED_SVC_CHECK;localhost;ssh;1382115705
    [1382115706] EXTERNAL COMMAND: SCHEDULE_FORCED_SVC_CHECK;localhost;users;1382115705
    [1382115731] EXTERNAL COMMAND: PROCESS_SERVICE_CHECK_RESULT;localhost;ping6;2;critical test|
    [1382115731] SERVICE ALERT: localhost;ping6;CRITICAL;SOFT;2;critical test



## <a id="check-result-files"></a> Check Result Files

Icinga 1.x writes its check result files into a temporary spool directory
where it reads these check result files in a regular interval from.
While this is extremly inefficient in performance regards it has been
rendered useful for passing passive check results directly into Icinga 1.x
skipping the external command pipe.

Several clustered/distributed environments and check-aggregation addons
use that method. In order to support step-by-step migration of these
environments, Icinga 2 ships the `CheckResultReader` object.

There is no feature configuration available, but it must be defined
on-demand in your Icinga 2 objects configuration.

    object CheckResultReader "reader" {
      spool_dir = "/data/check-results"
    }