fix depends on behavior and simplify some of its logic (#908)

* fix depends on behavior and simplify some of its logic

* fix comments

cmd/root.go

@@ -154,9 +154,18 @@ func Run(c *cobra.Command, names []string) {
 	runOnce, _ := c.PersistentFlags().GetBool("run-once")
 	enableUpdateAPI, _ := c.PersistentFlags().GetBool("http-api-update")
 	enableMetricsAPI, _ := c.PersistentFlags().GetBool("http-api-metrics")
-
 	apiToken, _ := c.PersistentFlags().GetString("http-api-token")
 
+	if rollingRestart && monitorOnly {
+		log.Fatal("Rolling restarts is not compatible with the global monitor only flag")
+	}
+
+	awaitDockerClient()
+
+	if err := actions.CheckForSanity(client, filter, rollingRestart); err != nil {
+		logNotifyExit(err)
+	}
+
 	if runOnce {
 		writeStartupMessage(c, time.Time{}, filterDesc)
 		runUpdatesWithNotifications(filter)
@@ -166,7 +175,7 @@ func Run(c *cobra.Command, names []string) {
 	}
 
 	if err := actions.CheckForMultipleWatchtowerInstances(client, cleanup, scope); err != nil {
-		log.Fatal(err)
+		logNotifyExit(err)
 	}
 
 	httpAPI := api.New(apiToken)
@@ -192,6 +201,17 @@ func Run(c *cobra.Command, names []string) {
 	os.Exit(1)
 }
 
+func logNotifyExit(err error) {
+	log.Error(err)
+	notifier.Close()
+	os.Exit(1)
+}
+
+func awaitDockerClient() {
+	log.Debug("Sleeping for a second to ensure the docker api client has been properly initialized.")
+	time.Sleep(1 * time.Second)
+}
+
 func formatDuration(d time.Duration) string {
 	sb := strings.Builder{}
 

internal/actions/check.go

@@ -2,28 +2,47 @@ package actions
 
 import (
 	"fmt"
+	"github.com/containrrr/watchtower/pkg/types"
 	"sort"
 	"time"
 
 	"github.com/containrrr/watchtower/pkg/filters"
 	"github.com/containrrr/watchtower/pkg/sorter"
-	"github.com/sirupsen/logrus"
 
 	log "github.com/sirupsen/logrus"
 
 	"github.com/containrrr/watchtower/pkg/container"
 )
 
+// CheckForSanity makes sure everything is sane before starting
+func CheckForSanity(client container.Client, filter types.Filter, rollingRestarts bool) error {
+	log.Debug("Making sure everything is sane before starting")
+
+	if rollingRestarts {
+		containers, err := client.ListContainers(filter)
+		if err != nil {
+			return err
+		}
+		for _, c := range containers {
+			if len(c.Links()) > 0 {
+				return fmt.Errorf(
+					"%q is depending on at least one other container. This is not compatible with rolling restarts",
+					c.Name(),
+				)
+			}
+		}
+	}
+	return nil
+}
+
 // CheckForMultipleWatchtowerInstances will ensure that there are not multiple instances of the
 // watchtower running simultaneously. If multiple watchtower containers are detected, this function
 // will stop and remove all but the most recently started container. This behaviour can be bypassed
 // if a scope UID is defined.
 func CheckForMultipleWatchtowerInstances(client container.Client, cleanup bool, scope string) error {
-	awaitDockerClient()
 	containers, err := client.ListContainers(filters.FilterByScope(scope, filters.WatchtowerContainersFilter))
 
 	if err != nil {
-		log.Fatal(err)
 		return err
 	}
 
@@ -45,14 +64,14 @@ func cleanupExcessWatchtowers(containers []container.Container, client container
 	for _, c := range allContainersExceptLast {
 		if err := client.StopContainer(c, 10*time.Minute); err != nil {
 			// logging the original here as we're just returning a count
-			logrus.WithError(err).Error("Could not stop a previous watchtower instance.")
+			log.WithError(err).Error("Could not stop a previous watchtower instance.")
 			stopErrors++
 			continue
 		}
 
 		if cleanup {
 			if err := client.RemoveImageByID(c.ImageID()); err != nil {
-				logrus.WithError(err).Warning("Could not cleanup watchtower images, possibly because of other watchtowers instances in other scopes.")
+				log.WithError(err).Warning("Could not cleanup watchtower images, possibly because of other watchtowers instances in other scopes.")
 			}
 		}
 	}
@@ -63,8 +82,3 @@ func cleanupExcessWatchtowers(containers []container.Container, client container
 
 	return nil
 }
-
-func awaitDockerClient() {
-	log.Debug("Sleeping for a second to ensure the docker api client has been properly initialized.")
-	time.Sleep(1 * time.Second)
-}

internal/actions/update.go

@@ -50,6 +50,7 @@ func Update(client container.Client, params types.UpdateParams) (*metrics2.Metri
 	}
 
 	containers, err = sorter.SortByDependencies(containers)
+
 	metric.Scanned = len(containers)
 	if err != nil {
 		return nil, err
@@ -57,11 +58,11 @@ func Update(client container.Client, params types.UpdateParams) (*metrics2.Metri
 
 	checkDependencies(containers)
 
-	containersToUpdate := []container.Container{}
+	var containersToUpdate []container.Container
 	if !params.MonitorOnly {
-		for i := len(containers) - 1; i >= 0; i-- {
+		for _, c := range containers {
-			if !containers[i].IsMonitorOnly() {
+			if !c.IsMonitorOnly() {
-				containersToUpdate = append(containersToUpdate, containers[i])
+				containersToUpdate = append(containersToUpdate, c)
 			}
 		}
 	}
@@ -86,7 +87,7 @@ func performRollingRestart(containers []container.Container, client container.Cl
 	failed := 0
 
 	for i := len(containers) - 1; i >= 0; i-- {
-		if containers[i].Stale {
+		if containers[i].ToRestart() {
 			if err := stopStaleContainer(containers[i], client, params); err != nil {
 				failed++
 			}
@@ -119,7 +120,7 @@ func stopStaleContainer(container container.Container, client container.Client,
 		return nil
 	}
 
-	if !container.Stale {
+	if !container.ToRestart() {
 		return nil
 	}
 	if params.LifecycleHooks {
@@ -143,7 +144,7 @@ func restartContainersInSortedOrder(containers []container.Container, client con
 	failed := 0
 
 	for _, c := range containers {
-		if !c.Stale {
+		if !c.ToRestart() {
 			continue
 		}
 		if err := restartStaleContainer(c, client, params); err != nil {
@@ -183,7 +184,7 @@ func restartStaleContainer(container container.Container, client container.Clien
 		if newContainerID, err := client.StartContainer(container); err != nil {
 			log.Error(err)
 			return err
-		} else if container.Stale && params.LifecycleHooks {
+		} else if container.ToRestart() && params.LifecycleHooks {
 			lifecycle.ExecutePostUpdateCommand(client, newContainerID)
 		}
 	}
@@ -192,16 +193,19 @@ func restartStaleContainer(container container.Container, client container.Clien
 
 func checkDependencies(containers []container.Container) {
 
-	for i, parent := range containers {
+	for _, c := range containers {
-		if parent.ToRestart() {
+		if c.ToRestart() {
 			continue
 		}
 
 	LinkLoop:
-		for _, linkName := range parent.Links() {
+		for _, linkName := range c.Links() {
-			for _, child := range containers {
+			for _, candidate := range containers {
-				if child.Name() == linkName && child.ToRestart() {
+				if candidate.Name() != linkName {
-					containers[i].Linked = true
+					continue
+				}
+				if candidate.ToRestart() {
+					c.LinkedToRestarting = true
 					break LinkLoop
 				}
 			}

pkg/container/container.go

@@ -22,7 +22,7 @@ func NewContainer(containerInfo *types.ContainerJSON, imageInfo *types.ImageInsp
 
 // Container represents a running Docker container.
 type Container struct {
-	Linked bool
+	LinkedToRestarting bool
 	Stale              bool
 
 	containerInfo *types.ContainerJSON
@@ -142,7 +142,7 @@ func (c Container) Links() []string {
 // ToRestart return whether the container should be restarted, either because
 // is stale or linked to another stale container.
 func (c Container) ToRestart() bool {
-	return c.Stale || c.Linked
+	return c.Stale || c.LinkedToRestarting
 }
 
 // IsWatchtower returns a boolean flag indicating whether or not the current

scripts/dependency-test.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+
+# Simulates a container that will always be updated, checking whether it shuts down it's dependencies correctly.
+
+docker rm -f parent || true
+docker rm -f depending || true
+
+CHANGE=redis:latest
+KEEP=tutum/hello-world
+
+docker tag tutum/hello-world:latest redis:latest
+
+docker run -d --name parent $CHANGE
+docker run -d --name depending --link parent $KEEP
+
+go run . --run-once --debug $@