introduce compose logs --index to select a replica container

Signed-off-by: Amit Saha <asaha@atlassian.com>
Signed-off-by: Nicolas De Loof <nicolas.deloof@gmail.com>

cmd/compose/logs.go

@@ -18,6 +18,7 @@ package compose
 
 import (
 	"context"
+	"errors"
 
 	"github.com/docker/cli/cli/command"
 	"github.com/spf13/cobra"
@@ -49,11 +50,17 @@ func logsCommand(p *ProjectOptions, dockerCli command.Cli, backend api.Service)
 		RunE: Adapt(func(ctx context.Context, args []string) error {
 			return runLogs(ctx, dockerCli, backend, opts, args)
 		}),
+		PreRunE: func(cmd *cobra.Command, args []string) error {
+			if opts.index > 0 && len(args) != 1 {
+				return errors.New("--index requires one service to be selected")
+			}
+			return nil
+		},
 		ValidArgsFunction: completeServiceNames(dockerCli, p),
 	}
 	flags := logsCmd.Flags()
 	flags.BoolVarP(&opts.follow, "follow", "f", false, "Follow log output.")
-	flags.IntVar(&opts.index, "index", 1, "index of the container if there are multiple instances of a service [default: 1].")
+	flags.IntVar(&opts.index, "index", 0, "index of the container if service has multiple replicas")
 	flags.StringVar(&opts.since, "since", "", "Show logs since timestamp (e.g. 2013-01-02T13:23:37Z) or relative (e.g. 42m for 42 minutes)")
 	flags.StringVar(&opts.until, "until", "", "Show logs before a timestamp (e.g. 2013-01-02T13:23:37Z) or relative (e.g. 42m for 42 minutes)")
 	flags.BoolVar(&opts.noColor, "no-color", false, "Produce monochrome output.")
@@ -73,6 +80,7 @@ func runLogs(ctx context.Context, dockerCli command.Cli, backend api.Service, op
 		Project:    project,
 		Services:   services,
 		Follow:     opts.follow,
+		Index:      opts.index,
 		Tail:       opts.tail,
 		Since:      opts.since,
 		Until:      opts.until,

docs/reference/compose_logs.md

@@ -9,7 +9,7 @@ View output from containers
 |:---------------------|:---------|:--------|:-----------------------------------------------------------------------------------------------|
 | `--dry-run`          |          |         | Execute command in dry run mode                                                                |
 | `-f`, `--follow`     |          |         | Follow log output.                                                                             |
-| `--index`            | `int`    | `1`     | index of the container if there are multiple instances of a service [default: 1].              |
+| `--index`            | `int`    | `0`     | index of the container if service has multiple replicas                                        |
 | `--no-color`         |          |         | Produce monochrome output.                                                                     |
 | `--no-log-prefix`    |          |         | Don't print prefix in logs.                                                                    |
 | `--since`            | `string` |         | Show logs since timestamp (e.g. 2013-01-02T13:23:37Z) or relative (e.g. 42m for 42 minutes)    |

docs/reference/docker_compose_logs.yaml

@@ -18,9 +18,8 @@ options:
       swarm: false
     - option: index
       value_type: int
-      default_value: "1"
-      description: |
-        index of the container if there are multiple instances of a service [default: 1].
+      default_value: "0"
+      description: index of the container if service has multiple replicas
       deprecated: false
       hidden: false
       experimental: false

pkg/api/api.go

@@ -488,6 +488,7 @@ type ServiceStatus struct {
 // LogOptions defines optional parameters for the `Log` API
 type LogOptions struct {
 	Project    *types.Project
+	Index      int
 	Services   []string
 	Tail       string
 	Since      string

pkg/compose/logs.go

@@ -20,7 +20,6 @@ import (
 	"context"
 	"errors"
 	"io"
-	"strings"
 	"time"
 
 	"github.com/docker/docker/api/types"
@@ -39,12 +38,22 @@ func (s *composeService) Logs(
 	consumer api.LogConsumer,
 	options api.LogOptions,
 ) error {
-	projectName = strings.ToLower(projectName)
 
-	containers, err := s.getContainers(ctx, projectName, oneOffExclude, true, options.Services...)
+	var containers Containers
+	var err error
+
+	if options.Index > 0 {
+		container, err := s.getSpecifiedContainer(ctx, projectName, oneOffExclude, true, options.Services[0], options.Index)
 		if err != nil {
 			return err
 		}
+		containers = append(containers, container)
+	} else {
+		containers, err = s.getContainers(ctx, projectName, oneOffExclude, true, options.Services...)
+		if err != nil {
+			return err
+		}
+	}
 
 	if options.Project != nil && len(options.Services) == 0 {
 		// we run with an explicit compose.yaml, so only consider services defined in this file