// 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 err != nil {
return fmt.Errorf("%s is not in state: %v", tag, err)
}
if len(containers) == 0 {
if err := machine.SupportsNoContainers(); err != nil {
return fmt.Errorf("clearing supported containers for %s: %v", tag, err)
}
return nil
}
if err := machine.SetSupportedContainers(containers...); err != nil {
return fmt.Errorf("setting supported containers for %s: %v", tag, err)
}
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
}