对于DeploymentController来说，需要监听Deployment,RS和Pod。从Controller的创建过程中可以看出来。
dc.dStore.Store, dc.dController = framework.NewInformer( &cache.ListWatch{ ListFunc: func(options api.ListOptions) (runtime.Object, error) { return dc.client.Extensions().Deployments(api.NamespaceAll).List(options) }, WatchFunc: func(options api.ListOptions) (watch.Interface, error) { return dc.client.Extensions().Deployments(api.NamespaceAll).Watch(options) }, }, &extensions.Deployment{}, FullDeploymentResyncPeriod, framework.ResourceEventHandlerFuncs{ AddFunc: dc.addDeploymentNotification, UpdateFunc: dc.updateDeploymentNotification, // This will enter the sync loop and no-op, because the deployment has been deleted from the store. DeleteFunc: dc.deleteDeploymentNotification, }, ) dc.rsStore.Store, dc.rsController = framework.NewInformer( &cache.ListWatch{ ListFunc: func(options api.ListOptions) (runtime.Object, error) { return dc.client.Extensions().ReplicaSets(api.NamespaceAll).List(options) }, WatchFunc: func(options api.ListOptions) (watch.Interface, error) { return dc.client.Extensions().ReplicaSets(api.NamespaceAll).Watch(options) }, }, &extensions.ReplicaSet{}, resyncPeriod(), framework.ResourceEventHandlerFuncs{ AddFunc: dc.addReplicaSet, UpdateFunc: dc.updateReplicaSet, DeleteFunc: dc.deleteReplicaSet, }, ) dc.podStore.Indexer, dc.podController = framework.NewIndexerInformer( &cache.ListWatch{ ListFunc: func(options api.ListOptions) (runtime.Object, error) { return dc.client.Core().Pods(api.NamespaceAll).List(options) }, WatchFunc: func(options api.ListOptions) (watch.Interface, error) { return dc.client.Core().Pods(api.NamespaceAll).Watch(options) }, }, &api.Pod{}, resyncPeriod(), framework.ResourceEventHandlerFuncs{ AddFunc: dc.addPod, UpdateFunc: dc.updatePod, DeleteFunc: dc.deletePod, }, cache.Indexers{cache.NamespaceIndex: cache.MetaNamespaceIndexFunc}, ) dc.syncHandler = dc.syncDeployment dc.dStoreSynced = dc.dController.HasSynced dc.rsStoreSynced = dc.rsController.HasSynced dc.podStoreSynced = dc.podController.HasSynced这里最核心的就是syncDeployment，因为这里面有rollingUpdate和rollback的实现。在这里如果watch到某个Deployment对象的RollbackTo.Revision部位nil,则执行rollingbach。这个Revision是版本号，注意虽然是回滚，但k8s内部记录的版本号永远是增长的。
有人会好奇,rollback是怎么做到的，其实原理很简单，k8s记录了各个版本的PodTemplate,把旧的PodTemplate覆盖新的Template即可。
对于K8S来说，升级有两种方式，一种是重新构建，一种是滚动升级。