// updateSupportedContainers records in state that a machine can run the specified containers. // It starts a watcher and when a container of a given type is first added to the machine, // the watcher is killed, the machine is set up to be able to start containers of the given type, // and a suitable provisioner is started. func (a *MachineAgent) updateSupportedContainers( runner worker.Runner, st *api.State, machineTag string, containers []instance.ContainerType, agentConfig agent.Config, ) error { pr := st.Provisioner() tag, err := names.ParseMachineTag(machineTag) if err != nil { return err } machine, err := pr.Machine(tag) if errors.IsNotFound(err) || err == nil && machine.Life() == params.Dead { return worker.ErrTerminateAgent } if err != nil { return errors.Annotatef(err, "cannot load machine %s from state", tag) } if len(containers) == 0 { if err := machine.SupportsNoContainers(); err != nil { return errors.Annotatef(err, "clearing supported containers for %s", tag) } return nil } if err := machine.SetSupportedContainers(containers...); err != nil { return errors.Annotatef(err, "setting supported containers for %s", tag) } initLock, err := hookExecutionLock(agentConfig.DataDir()) if err != nil { return err } // Start the watcher to fire when a container is first requested on the machine. watcherName := fmt.Sprintf("%s-container-watcher", machine.Id()) handler := provisioner.NewContainerSetupHandler( runner, watcherName, containers, machine, pr, agentConfig, initLock, ) a.startWorkerAfterUpgrade(runner, watcherName, func() (worker.Worker, error) { return worker.NewStringsWorker(handler), nil }) return nil }