# Pod deletion

## 1. 代码

所有的rest请求都会转到api server，由apiserver处理。

`staging/src/k8s.io/apiserver/pkg/registry/generic/registry/store.go`（其他接口也在这，比如: `GET`）

```
// Delete removes the item from storage.
func (e *Store) Delete(ctx genericapirequest.Context, name string, options *metav1.DeleteOptions) (runtime.Object, bool, error)
```

参数里有个`DeleteOptions`，是为了实现graceful shutdown。

`staging/src/k8s.io/apiserver/pkg/endpoints/installer.go`在install rest api handler时会对这种支持`DeleteOptions`的handler进行特殊处理，从http body里取出delete options相关的参数。

```
func (a *APIInstaller) registerResourceHandlers(path string, storage rest.Storage, ws *restful.WebService, proxyHandler http.Handler) (*metav1.APIResource, error) {
    ...
    gracefulDeleter, isGracefulDeleter := storage.(rest.GracefulDeleter)
    ...
    switch {
    case isGracefulDeleter:
        versionedDeleteOptions, err = a.group.Creater.New(optionsExternalVersion.WithKind("DeleteOptions"))
        if err != nil {
            return nil, err
        }
        versionedDeleterObject = indirectArbitraryPointer(versionedDeleteOptions)
        isDeleter = true
    case isDeleter:
        gracefulDeleter = rest.GracefulDeleteAdapter{Deleter: deleter}
    }
    ...
            case "DELETE": // Delete a resource.
            article := getArticleForNoun(kind, " ")
            doc := "delete" + article + kind
            if hasSubresource {
                doc = "delete " + subresource + " of" + article + kind
            }
            handler := metrics.InstrumentRouteFunc(action.Verb, resource, subresource, requestScope, restfulDeleteResource(gracefulDeleter, isGracefulDeleter, reqScope, admit))
            route := ws.DELETE(action.Path).To(handler).
                Doc(doc).
                Param(ws.QueryParameter("pretty", "If 'true', then the output is pretty printed.")).
                Operation("delete"+namespaced+kind+strings.Title(subresource)+operationSuffix).
                Produces(append(storageMeta.ProducesMIMETypes(action.Verb), mediaTypes...)...).
                Writes(versionedStatus).
                Returns(http.StatusOK, "OK", versionedStatus)
            if isGracefulDeleter {
                route.Reads(versionedDeleterObject)
                if err := addObjectParams(ws, route, versionedDeleteOptions); err != nil {
                    return nil, err
                }
            }
            addParams(route, action.Params)
            routes = append(routes, route)
}
```

注意：如果是`gracefulDeleter`，则最终传给`store.go#Delete`函数的options参数一定不为nil。

删除pod的接口如下：

```
Delete(name string, options *meta_v1.DeleteOptions)
```

`options`为`nil`时，将会使用default graceful period(默认为30s)。如果要强制直接从etcd上把pod删除，可以指定graceful period为0（`metav1.NewDeleteOptions(0)`）。具体的例子可见[https://github.com/coreos/etcd-operator/pull/273。](https://github.com/coreos/etcd-operator/pull/273%E3%80%82)

最后，Pod etcd strategy在文件夹`pkg/registry/core/pod`下。

## 2. Issue

* Proposal - Pod safety and termination guarantees: <https://github.com/kubernetes/kubernetes/pull/34160>
* Make StatefulSets safe during cluster failure: <https://github.com/kubernetes/features/issues/119>
* Node status down -> pod status unknown -> pod cant be deleted, cordon doesnt finish.: <https://github.com/kubernetes/kubernetes/issues/51333>
* Graceful delete
  * Consistently support graceful and immediate termination for all objects: <https://github.com/kubernetes/kubernetes/issues/1535>
  * Deleting pods and other resources with graceful shutdown: <https://github.com/kubernetes/kubernetes/issues/2789>
* 具体的应用，怎么删除一个pod

  k8s: delete pod with 0 grace period: <https://github.com/coreos/etcd-operator/pull/273>

## 3. 参考资料

* Pod Safety, Consistency Guarantees, and Storage Implications: <https://github.com/kubernetes/community/blob/master/contributors/design-proposals/storage/pod-safety.md>

  保证at most on instance，避免多实例，对statefulset格外重要
* Termination of Pods: <https://kubernetes.io/docs/concepts/workloads/pods/pod/#termination-of-pods>