Add support for onshutdown

This is a list of images to run on a clean shutdown. Note that you must not rely on these
being run at all, as machines may be be powered off or shut down without having time to run
these scripts. If you add anything here you should test both in the case where they are
run and when they are not. Most systems are likely to be "crash only" and not have any setup here,
but you can attempt to deregister cleanly from a network service here, rather than relying
on timeouts, for example.

Fix https://github.com/linuxkit/linuxkit/issues/1988

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

src/moby/build.go

@@ -133,6 +133,10 @@ func Build(m Moby, w io.Writer, pull bool, tp string) error {
 		idMap[image.Name] = id
 		id++
 	}
+	for _, image := range m.Onshutdown {
+		idMap[image.Name] = id
+		id++
+	}
 	for _, image := range m.Services {
 		idMap[image.Name] = id
 		id++
@@ -182,6 +186,24 @@ func Build(m Moby, w io.Writer, pull bool, tp string) error {
 		}
 	}
 
+	if len(m.Onshutdown) != 0 {
+		log.Infof("Add onshutdown containers:")
+	}
+	for i, image := range m.Onshutdown {
+		log.Infof("  Create OCI config for %s", image.Image)
+		useTrust := enforceContentTrust(image.Image, &m.Trust)
+		config, err := ConfigToOCI(image, useTrust, idMap)
+		if err != nil {
+			return fmt.Errorf("Failed to create config.json for %s: %v", image.Image, err)
+		}
+		so := fmt.Sprintf("%03d", i)
+		path := "containers/onshutdown/" + so + "-" + image.Name
+		err = ImageBundle(path, image.Image, config, iw, useTrust, pull)
+		if err != nil {
+			return fmt.Errorf("Failed to extract root filesystem for %s: %v", image.Image, err)
+		}
+	}
+
 	if len(m.Services) != 0 {
 		log.Infof("Add service containers:")
 	}

src/moby/config.go

@@ -19,12 +19,13 @@ import (
 
 // Moby is the type of a Moby config file
 type Moby struct {
-	Kernel   KernelConfig `kernel:"cmdline" json:"kernel,omitempty"`
-	Init     []string     `init:"cmdline" json:"init"`
-	Onboot   []Image      `yaml:"onboot" json:"onboot"`
-	Services []Image      `yaml:"services" json:"services"`
-	Trust    TrustConfig  `yaml:"trust" json:"trust,omitempty"`
-	Files    []File       `yaml:"files" json:"files"`
+	Kernel     KernelConfig `kernel:"cmdline" json:"kernel,omitempty"`
+	Init       []string     `init:"cmdline" json:"init"`
+	Onboot     []Image      `yaml:"onboot" json:"onboot"`
+	Onshutdown []Image      `yaml:"onshutdown" json:"onshutdown"`
+	Services   []Image      `yaml:"services" json:"services"`
+	Trust      TrustConfig  `yaml:"trust" json:"trust,omitempty"`
+	Files      []File       `yaml:"files" json:"files"`
 }
 
 // KernelConfig is the type of the config for a kernel
@@ -182,6 +183,7 @@ func AppendConfig(m0, m1 Moby) (Moby, error) {
 	}
 	moby.Init = append(moby.Init, m1.Init...)
 	moby.Onboot = append(moby.Onboot, m1.Onboot...)
+	moby.Onshutdown = append(moby.Onshutdown, m1.Onshutdown...)
 	moby.Services = append(moby.Services, m1.Services...)
 	moby.Files = append(moby.Files, m1.Files...)
 	moby.Trust.Image = append(moby.Trust.Image, m1.Trust.Image...)

src/moby/schema.go

@@ -128,6 +128,7 @@ var schema = string(`
     "kernel": { "$ref": "#/definitions/kernel" },
     "init": { "$ref": "#/definitions/strings" },
     "onboot": { "$ref": "#/definitions/images" },
+    "onshutdown": { "$ref": "#/definitions/images" },
     "services": { "$ref": "#/definitions/images" },
     "trust": { "$ref": "#/definitions/trust" },
     "files": { "$ref": "#/definitions/files" }