Update docs

doc/99-redis.md

@@ -1,4 +1,46 @@
-### Keys
+# Icinga2 Redis <a id="icinga-redis"></a>
+## Subscriptions and events
+
+Using the redis feature allows you to add subscriptions for events which will then be served by Icinga 2 over Redis.
+
+Possible event types:
+
+* CheckResult
+* StateChange
+* Notification
+* AcknowledgementSet
+* AcknowledgementCleared
+* CommentAdded
+* CommentRemoved
+* DowntimeAdded
+* DowntimeRemoved
+* DowntimeStarted
+* DowntimeTriggered
+
+### Creating a subscription
+A subscription is created by creating a new key `icinga:subscription:<name>` in redis with a set of event types. All 
+events matching the the type of those listed will then be added to a list at `icinga:event:<name>`. The events are 
+rotated on a first-in-first-out basis, the default limit is (TODO) and can be overwritten by setting 
+`icinga:subscription:<name>:limit` to the desired ammount.
+
+The events are saved as json encoded strings, similar to the API.
+
+It is recommended to use `LPOP` to read from the list and discard read events at the same time.
+
+Example:
+
+```
+$ redis-cli
+127.0.0.1:6379> SADD icinga:subscription:noma-2 "Notification" "CheckResult"
+(integer) 2
+127.0.0.1:6379> SET icinga:subscription:noma-2:limit 500
+OK
+...
+127.0.0.1:6379> LRANGE icinga:event:noma-2 0 1
+1) "{\"check_result\":{\"active\":true,\"check_source\":\"icinga-1\",\"command\":[\"/usr/lib/nagios/plugins/check_ping\" ... ]}}"
+1) "{\"check_result\":{\"active\":true,\"check_source\":\"icinga-2\",\"command\":[\"/usr/lib/nagios/plugins/check_ping\" ... ]}}"
+```
+
 
 All Keys are prefixed with "icinga:"
 
@@ -10,4 +52,3 @@ config:{type}          | Hash   | Config          | Has all the config with name
 config:{type}:checksum | Hash   | Checksums       | Key is name, returns a json encoded string of checksums
 subscription:{name}    | String | sub description | json string describing the subsciption
 event:{name}           | List   | sub output      | Publish endpoint for subscription of the same name
-:trigger::configchange | List   | ?               | I have no idea what this is or where it comes from