backport container restart support in loki source

CHANGELOG.md

@@ -87,6 +87,8 @@ Main (unreleased)
 - Fix an issue on Windows where uninstalling Alloy did not remove it from the
   Add/Remove programs list. (@rfratto)
 
+- Fix an issue where `loki.source.docker` stops collecting logs after a container restart. (@wildum)
+
 ### Other changes
 
 - Clustering for Grafana Agent in Flow mode has graduated from beta to stable.

internal/component/loki/source/docker/docker.go

@@ -305,9 +305,10 @@ func (c *Component) getManagerOptions(args Arguments) (*options, error) {
 	}
 
 	return &options{
-		client:    client,
-		handler:   loki.NewEntryHandler(c.handler.Chan(), func() {}),
-		positions: c.posFile,
+		client:                client,
+		handler:               loki.NewEntryHandler(c.handler.Chan(), func() {}),
+		positions:             c.posFile,
+		targetRestartInterval: 5 * time.Second,
 	}, nil
 }
 

internal/component/loki/source/docker/docker_test.go

@@ -4,17 +4,32 @@ package docker
 
 import (
 	"context"
+	"io"
+	"os"
+	"strings"
 	"testing"
 	"time"
 
+	"github.com/docker/docker/api/types"
+	"github.com/docker/docker/api/types/container"
+	"github.com/docker/docker/client"
+	"github.com/go-kit/log"
 	"github.com/grafana/agent/internal/component"
+	"github.com/grafana/agent/internal/component/common/loki/client/fake"
+	"github.com/grafana/agent/internal/component/common/loki/positions"
+	dt "github.com/grafana/agent/internal/component/loki/source/docker/internal/dockertarget"
 	"github.com/grafana/agent/internal/flow/componenttest"
 	"github.com/grafana/agent/internal/util"
 	"github.com/grafana/river"
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/common/model"
+	"github.com/prometheus/prometheus/model/relabel"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
+const targetRestartInterval = 20 * time.Millisecond
+
 func Test(t *testing.T) {
 	// Use host that works on all platforms (including Windows).
 	var cfg = `
@@ -73,3 +88,93 @@ func TestDuplicateTargets(t *testing.T) {
 
 	require.Len(t, cmp.manager.tasks, 1)
 }
+
+func TestRestart(t *testing.T) {
+	runningState := true
+	client := clientMock{
+		logLine: "2024-05-02T13:11:55.879889Z caller=module_service.go:114 msg=\"module stopped\" module=distributor",
+		running: func() bool { return runningState },
+	}
+	expectedLogLine := "caller=module_service.go:114 msg=\"module stopped\" module=distributor"
+
+	tailer, entryHandler := setupTailer(t, client)
+	go tailer.Run(context.Background())
+
+	// The container is already running, expect log lines.
+	assert.EventuallyWithT(t, func(c *assert.CollectT) {
+		logLines := entryHandler.Received()
+		if assert.NotEmpty(c, logLines) {
+			assert.Equal(c, expectedLogLine, logLines[0].Line)
+		}
+	}, time.Second, 20*time.Millisecond, "Expected log lines were not found within the time limit.")
+
+	// Stops the container.
+	runningState = false
+	time.Sleep(targetRestartInterval + 10*time.Millisecond) // Sleep for a duration greater than targetRestartInterval to make sure it stops sending log lines.
+	entryHandler.Clear()
+	time.Sleep(targetRestartInterval + 10*time.Millisecond)
+	assert.Empty(t, entryHandler.Received()) // No log lines because the container was not running.
+
+	// Restart the container and expect log lines.
+	runningState = true
+	assert.EventuallyWithT(t, func(c *assert.CollectT) {
+		logLines := entryHandler.Received()
+		if assert.NotEmpty(c, logLines) {
+			assert.Equal(c, expectedLogLine, logLines[0].Line)
+		}
+	}, time.Second, 20*time.Millisecond, "Expected log lines were not found within the time limit after restart.")
+}
+
+func setupTailer(t *testing.T, client clientMock) (tailer *tailer, entryHandler *fake.Client) {
+	w := log.NewSyncWriter(os.Stderr)
+	logger := log.NewLogfmtLogger(w)
+	entryHandler = fake.NewClient(func() {})
+
+	ps, err := positions.New(logger, positions.Config{
+		SyncPeriod:    10 * time.Second,
+		PositionsFile: t.TempDir() + "/positions.yml",
+	})
+	require.NoError(t, err)
+
+	tgt, err := dt.NewTarget(
+		dt.NewMetrics(prometheus.NewRegistry()),
+		logger,
+		entryHandler,
+		ps,
+		"flog",
+		model.LabelSet{"job": "docker"},
+		[]*relabel.Config{},
+		client,
+	)
+	require.NoError(t, err)
+	tailerTask := &tailerTask{
+		options: &options{
+			client:                client,
+			targetRestartInterval: targetRestartInterval,
+		},
+		target: tgt,
+	}
+	return newTailer(logger, tailerTask), entryHandler
+}
+
+type clientMock struct {
+	client.APIClient
+	logLine string
+	running func() bool
+}
+
+func (mock clientMock) ContainerInspect(ctx context.Context, c string) (types.ContainerJSON, error) {
+	return types.ContainerJSON{
+		ContainerJSONBase: &types.ContainerJSONBase{
+			ID: c,
+			State: &types.ContainerState{
+				Running: mock.running(),
+			},
+		},
+		Config: &container.Config{Tty: true},
+	}, nil
+}
+
+func (mock clientMock) ContainerLogs(ctx context.Context, container string, options types.ContainerLogsOptions) (io.ReadCloser, error) {
+	return io.NopCloser(strings.NewReader(mock.logLine)), nil
+}

internal/component/loki/source/docker/internal/dockertarget/target.go

@@ -230,8 +230,6 @@ func (t *Target) StartIfNotRunning() {
 		ctx, cancel := context.WithCancel(context.Background())
 		t.cancel = cancel
 		go t.processLoop(ctx)
-	} else {
-		level.Debug(t.logger).Log("msg", "attempted to start process loop but it's already running", "container", t.containerName)
 	}
 }
 

internal/component/loki/source/docker/runner.go

@@ -5,8 +5,8 @@ package docker
 import (
 	"context"
 	"sync"
+	"time"
 
-	"github.com/docker/docker/api/types/container"
 	"github.com/docker/docker/client"
 	"github.com/go-kit/log"
 	"github.com/grafana/agent/internal/component/common/loki"
@@ -52,6 +52,9 @@ type options struct {
 
 	// positions interface so tailers can save/restore offsets in log files.
 	positions positions.Positions
+
+	// targetRestartInterval to restart task that has stopped running.
+	targetRestartInterval time.Duration
 }
 
 // tailerTask is the payload used to create tailers. It implements runner.Task.
@@ -95,23 +98,25 @@ func newTailer(l log.Logger, task *tailerTask) *tailer {
 }
 
 func (t *tailer) Run(ctx context.Context) {
-	ch, chErr := t.opts.client.ContainerWait(ctx, t.target.Name(), container.WaitConditionNextExit)
-
-	t.target.StartIfNotRunning()
-
-	select {
-	case err := <-chErr:
-		// Error setting up the Wait request from the client; either failed to
-		// read from /containers/{containerID}/wait, or couldn't parse the
-		// response. Stop the target and exit the task after logging; if it was
-		// a transient error, the target will be retried on the next discovery
-		// refresh.
-		level.Error(t.log).Log("msg", "could not set up a wait request to the Docker client", "error", err)
-		t.target.Stop()
-		return
-	case <-ch:
-		t.target.Stop()
-		return
+	ticker := time.NewTicker(t.opts.targetRestartInterval)
+	tickerC := ticker.C
+
+	for {
+		select {
+		case <-tickerC:
+			res, err := t.opts.client.ContainerInspect(ctx, t.target.Name())
+			if err != nil {
+				level.Error(t.log).Log("msg", "error inspecting Docker container", "id", t.target.Name(), "error", err)
+				continue
+			}
+			if res.State.Running {
+				t.target.StartIfNotRunning()
+			}
+		case <-ctx.Done():
+			t.target.Stop()
+			ticker.Stop()
+			return
+		}
 	}
 }