config: exclude known cached images

Author: adnxn

agent/config/config.go

@@ -126,6 +126,10 @@ const (
 
 	// DefaultTaskMetadataBurstRate is set to handle 60 burst requests at once
 	DefaultTaskMetadataBurstRate = 60
+
+	//Known cached image names
+	CachedImageNamePauseContainer = "amazon/amazon-ecs-pause:0.1.0"
+	CachedImageNameAgentContainer = "amazon/amazon-ecs-agent:latest"
 )
 
 const (

agent/config/config_test.go

@@ -376,7 +376,8 @@ func TestValidForImagesCleanupExclusion(t *testing.T) {
 	defer setTestRegion()()
 	defer setTestEnv("ECS_EXCLUDE_UNTRACKED_IMAGE", "amazonlinux:2,amazonlinux:3")()
 	imagesNotDelete := parseImageCleanupExclusionList("ECS_EXCLUDE_UNTRACKED_IMAGE")
-	assert.Equal(t, []string{"amazonlinux:2", "amazonlinux:3"}, imagesNotDelete, "unexpected imageCleanupExclusionList")
+	expectedImages := []string{"amazonlinux:2", "amazonlinux:3", CachedImageNameAgentContainer, CachedImageNamePauseContainer}
+	assert.Equal(t, expectedImages, imagesNotDelete, "unexpected imageCleanupExclusionList")
 }
 
 func TestValidFormatParseEnvVariableDuration(t *testing.T) {

agent/config/parse.go

@@ -298,6 +298,10 @@ func parseImageCleanupExclusionList(envVar string) []string {
 	} else {
 		imageCleanupExclusionList = strings.Split(imageEnv, ",")
 	}
+
+	// append known cached internal images to imageCleanupExclusionLis
+	imageCleanupExclusionList = append(imageCleanupExclusionList, CachedImageNameAgentContainer, CachedImageNamePauseContainer)
+
 	for _, image := range imageCleanupExclusionList {
 		seelog.Infof("Image excluded from cleanup: %s", image)
 	}