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graph.go
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graph.go
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// Copyright 2014-2015 Amazon.com, Inc. or its affiliates. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License"). You may
// not use this file except in compliance with the License. A copy of the
// License is located at
//
// http://aws.amazon.com/apache2.0/
//
// or in the "license" file accompanying this file. This file is distributed
// on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
// express or implied. See the License for the specific language governing
// permissions and limitations under the License.
package dependencygraph
import (
"strings"
"github.com/aws/amazon-ecs-agent/agent/api"
"github.com/aws/amazon-ecs-agent/agent/logger"
)
var log = logger.ForModule("dependencygraph")
// Because a container may depend on another container being created
// (volumes-from) or running (links) it makes sense to abstract it out
// to each container having dependencies on another container being in any
// perticular state set. For now, these are resolved here and support only
// volume/link (created/run)
// ValidDependencies takes a task and verifies that it is possible to allow all
// containers within it to reach the desired status by proceeding in some order
func ValidDependencies(task *api.Task) bool {
unresolved := make([]*api.Container, len(task.Containers))
resolved := make([]*api.Container, 0, len(task.Containers))
copy(unresolved, task.Containers)
OuterLoop:
for len(unresolved) > 0 {
for i, tryResolve := range unresolved {
if dependenciesCanBeResolved(tryResolve, resolved) {
resolved = append(resolved, tryResolve)
unresolved = append(unresolved[:i], unresolved[i+1:]...)
// Break out of the inner loop now that we modified the slice
// we're looping over
continue OuterLoop
}
}
log.Warn("Could not resolve some containers", "task", task, "unresolved", unresolved)
return false
}
return true
}
func linksToContainerNames(links []string) []string {
names := make([]string, 0, len(links))
for _, link := range links {
name := strings.Split(link, ":")[0]
names = append(names, name)
}
return names
}
// DependenciesCanBeResolved verifies that it's possible to start a `target`
// given a group of already handled containers, `by`. Essentially, it asks "is
// `target` resolved by `by`". It assumes that everything in `by` has reached
// DesiredStatus and that `target` is also trying to get there
//
// This function is used for verifying that a state should be resolveable, not
// for actually deciding what to do. `DependenciesAreResolved` should be used for
// that purpose instead.
func dependenciesCanBeResolved(target *api.Container, by []*api.Container) bool {
nameMap := make(map[string]*api.Container)
for _, cont := range by {
nameMap[cont.Name] = cont
}
neededVolumeContainers := make([]string, len(target.VolumesFrom))
for i, volume := range target.VolumesFrom {
neededVolumeContainers[i] = volume.SourceContainer
}
return verifyStatusResolveable(target, nameMap, neededVolumeContainers, volumeCanResolve) &&
verifyStatusResolveable(target, nameMap, linksToContainerNames(target.Links), linkCanResolve)
}
// DependenciesAreResolved validates that the `target` container can be started
// given the current known state of the containers in `by`. If this function
// returns true, `target` should be technically able to launch with on issues
func DependenciesAreResolved(target *api.Container, by []*api.Container) bool {
nameMap := make(map[string]*api.Container)
for _, cont := range by {
nameMap[cont.Name] = cont
}
neededVolumeContainers := make([]string, len(target.VolumesFrom))
for i, volume := range target.VolumesFrom {
neededVolumeContainers[i] = volume.SourceContainer
}
return verifyStatusResolveable(target, nameMap, neededVolumeContainers, volumeIsResolved) &&
verifyStatusResolveable(target, nameMap, linksToContainerNames(target.Links), linkIsResolved) &&
verifyStatusResolveable(target, nameMap, target.RunDependencies, onRunIsResolved)
}
// verifyStatusResolveable validates that `target` can be resolved given that
// target depends on `dependencies` (which are container names) and there are
// `existingContainers` (map from name to container). The `resolves` function
// passed should return true if the named container is resolved.
func verifyStatusResolveable(target *api.Container, existingContainers map[string]*api.Container, dependencies []string, resolves func(*api.Container, *api.Container) bool) bool {
targetGoal := target.DesiredStatus
if targetGoal != api.ContainerRunning && targetGoal != api.ContainerCreated {
// A container can always stop, die, or reach whatever other statre it
// wants regardless of what dependencies it has
return true
}
for _, dependency := range dependencies {
maybeResolves, exists := existingContainers[dependency]
if !exists {
return false
}
if !resolves(target, maybeResolves) {
return false
}
}
return true
}
func linkCanResolve(target *api.Container, link *api.Container) bool {
if target.DesiredStatus == api.ContainerCreated {
return link.DesiredStatus == api.ContainerCreated || link.DesiredStatus == api.ContainerRunning
} else if target.DesiredStatus == api.ContainerRunning {
return link.DesiredStatus == api.ContainerRunning
}
log.Error("Unexpected desired status", "target", target)
return false
}
func linkIsResolved(target *api.Container, link *api.Container) bool {
if target.DesiredStatus == api.ContainerCreated {
return link.KnownStatus == api.ContainerCreated || link.KnownStatus == api.ContainerRunning
} else if target.DesiredStatus == api.ContainerRunning {
return link.KnownStatus == api.ContainerRunning
}
log.Error("Unexpected desired status", "target", target)
return false
}
func volumeCanResolve(target *api.Container, volume *api.Container) bool {
if target.DesiredStatus == api.ContainerCreated || target.DesiredStatus == api.ContainerRunning {
return volume.DesiredStatus == api.ContainerCreated ||
volume.DesiredStatus == api.ContainerRunning ||
volume.DesiredStatus == api.ContainerStopped
}
log.Error("Unexpected desired status", "target", target)
return false
}
func volumeIsResolved(target *api.Container, volume *api.Container) bool {
if target.DesiredStatus == api.ContainerCreated || target.DesiredStatus == api.ContainerRunning {
return volume.KnownStatus == api.ContainerCreated ||
volume.KnownStatus == api.ContainerRunning ||
volume.KnownStatus == api.ContainerStopped
}
log.Error("Unexpected desired status", "target", target)
return false
}
// onRunIsResolved defines a relationship where a target cannot be created until
// 'run' has reached a running state.
func onRunIsResolved(target *api.Container, run *api.Container) bool {
if target.DesiredStatus >= api.ContainerCreated {
return run.KnownStatus >= api.ContainerRunning
}
return false
}