feat: implement --pull policy for run command: always, missing, never

pkg/client/container.go

@@ -110,10 +110,25 @@ func (cli *Client) CreateContainer(
 
 	pw := progress.ContextWriter(ctx)
 	eventID := fmt.Sprintf("Container %s on %s", containerName, machine.Machine.Name)
-
 	pw.Event(progress.CreatingEvent(eventID))
+
+	if spec.Container.PullPolicy == api.PullPolicyAlways {
+		if err = cli.pullImageWithProgress(ctx, config.Image, machine.Machine.Name, eventID); err != nil {
+			return resp, err
+		}
+	}
+
 	resp, err = cli.Docker.CreateContainer(ctx, config, hostConfig, netConfig, nil, containerName)
 	if err != nil {
+		switch spec.Container.PullPolicy {
+		case api.PullPolicyAlways, api.PullPolicyNever:
+			return resp, err
+		case api.PullPolicyMissing:
+		default:
+			return resp, fmt.Errorf("unsupported pull policy: '%s'", spec.Container.PullPolicy)
+		}
+
+		// Not found error is expected if the image is missing.
 		if !dockerclient.IsErrNotFound(err) {
 			return resp, err
 		}

pkg/client/deploy/strategy.go

@@ -48,6 +48,7 @@ func (s *RollingStrategy) Plan(
 // planReplicated creates a plan for a replicated service deployment.
 // For replicated services, we want to maintain a specific number of containers (replicas) across the available machines
 // in the cluster.
+// TODO: schedule containers only on machines that contain the image if pull policy is set to 'never'.
 func (s *RollingStrategy) planReplicated(
 	ctx context.Context, cli api.MachineClient, svc *api.Service, spec api.ServiceSpec,
 ) (Plan, error) {