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。

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