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kube-apiserver: healthcheck via sidecar container
kube-apiserver doesn't expose the healthcheck via a dedicated endpoint, instead relying on anonyomous-access being enabled. That has previously forced us to enable the unauthenticated endpoint on 127.0.0.1:8080. Instead we now run a small sidecar container, which proxies /healthz and /readyz requests (only) adding appropriate authentication using a client certificate. This will also enable better load balancer checks in future, as these have previously been hampered by the custom CA certificate.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,64 @@ | ||
| load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library") | ||
|
|
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| go_library( | ||
| name = "go_default_library", | ||
| srcs = ["main.go"], | ||
| importpath = "k8s.io/kops/cmd/kube-apiserver-healthcheck", | ||
| visibility = ["//visibility:private"], | ||
| deps = ["//vendor/k8s.io/klog:go_default_library"], | ||
| ) | ||
|
|
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| go_binary( | ||
| name = "kube-apiserver-healthcheck", | ||
| embed = [":go_default_library"], | ||
| visibility = ["//visibility:public"], | ||
| ) | ||
|
|
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| load( | ||
| "@io_bazel_rules_docker//container:container.bzl", | ||
| "container_image", | ||
| "container_push", | ||
| "container_bundle", | ||
| ) | ||
|
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| container_image( | ||
| name = "image", | ||
| base = "@distroless_base//image", | ||
| cmd = ["/usr/bin/kube-apiserver-healthcheck"], | ||
| user = "10012", | ||
| directory = "/usr/bin/", | ||
| files = [ | ||
| "//cmd/kube-apiserver-healthcheck", | ||
| ], | ||
| stamp = True, | ||
| ) | ||
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| container_push( | ||
| name = "push-image", | ||
| format = "Docker", | ||
| image = ":image", | ||
| registry = "{STABLE_DOCKER_REGISTRY}", | ||
| repository = "{STABLE_DOCKER_IMAGE_PREFIX}kube-apiserver-healthcheck", | ||
| tag = "{STABLE_KUBE_APISERVER_HEALTHCHECK_TAG}", | ||
| ) | ||
|
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| container_bundle( | ||
| name = "image-bundle", | ||
| images = { | ||
| "{STABLE_DOCKER_IMAGE_PREFIX}kube-apiserver-healthcheck:{STABLE_KUBE_APISERVER_HEALTHCHECK_TAG}": "image", | ||
| }, | ||
| ) | ||
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| load("//tools:gzip.bzl", "gzip") | ||
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| gzip( | ||
| name = "image-bundle.tar.gz", | ||
| src = "image-bundle.tar", | ||
| ) | ||
|
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| load("//tools:hashes.bzl", "hashes") | ||
|
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||
| hashes( | ||
| name = "image-bundle.tar.gz.hashes", | ||
| src = "image-bundle.tar.gz", | ||
| ) |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,18 @@ | ||
| ## kube-apiserver-healthcheck | ||
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| This is a small sidecar container that allows for health-checking the | ||
| kube-apiserver without enabling anonymous authentication and without | ||
| enabling the unauthenticated port. | ||
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| It listens on port 8080 (http), and proxies a few known-safe requests | ||
| to the real apiserver listening on 443. It uses a client certificate | ||
| to authenticate itself to the apiserver. | ||
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| This lets us turn off the unauthenticated kube-apiserver endpoint, but | ||
| it also lets us have better load-balancer health-checks. | ||
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| Because it runs as a sidecar next to kube-apiserver, it is in the same | ||
| network namespace, and thus it can reach apiserver on | ||
| https://127.0.0.1 . The kube-apiserver-healthcheck process listens on | ||
| 8080, but the health checks for the apiserver container are configured | ||
| for :8080 and actually go via the sidecar. |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,164 @@ | ||
| /* | ||
| Copyright 2020 The Kubernetes Authors. | ||
| Licensed under the Apache License, Version 2.0 (the "License"); | ||
| you may not use this file except in compliance with the License. | ||
| You may obtain a copy of the License at | ||
| http://www.apache.org/licenses/LICENSE-2.0 | ||
| Unless required by applicable law or agreed to in writing, software | ||
| distributed under the License is distributed on an "AS IS" BASIS, | ||
| WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| See the License for the specific language governing permissions and | ||
| limitations under the License. | ||
| */ | ||
|
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| package main | ||
|
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||
| import ( | ||
| "crypto/tls" | ||
| "crypto/x509" | ||
| "flag" | ||
| "fmt" | ||
| "io" | ||
| "io/ioutil" | ||
| "net/http" | ||
| "net/url" | ||
| "os" | ||
|
|
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| "k8s.io/klog" | ||
| ) | ||
|
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| // healthCheckServer is the http server | ||
| type healthCheckServer struct { | ||
| transport *http.Transport | ||
| } | ||
|
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| // handler processes a single http request | ||
| func (s *healthCheckServer) handler(w http.ResponseWriter, r *http.Request) { | ||
| if r.Method == "GET" { | ||
| switch r.URL.Path { | ||
| case "/.kube-apiserver-healthcheck/healthz": | ||
| // This is a check for our own health | ||
| w.WriteHeader(http.StatusOK) | ||
| w.Write([]byte("ok")) | ||
| return | ||
|
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||
| case "/healthz", "/readyz": | ||
| // This is a health-check we will proxy | ||
| s.proxyRequest(w, r) | ||
| return | ||
| } | ||
| } | ||
|
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||
| klog.Infof("unknown request: %s %s", r.Method, r.URL.Path) | ||
| http.Error(w, "not found", http.StatusNotFound) | ||
| } | ||
|
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| // httpClient builds an isolated http.Client | ||
| func (s *healthCheckServer) httpClient() *http.Client { | ||
| return &http.Client{Transport: s.transport} | ||
| } | ||
|
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| // proxyRequest forwards a request, once it has been verified by handler | ||
| func (s *healthCheckServer) proxyRequest(w http.ResponseWriter, r *http.Request) { | ||
| httpClient := s.httpClient() | ||
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| u := &url.URL{ | ||
| Scheme: "https", | ||
| Host: "127.0.0.1", | ||
| Path: r.URL.Path, | ||
| RawQuery: r.URL.RawQuery, | ||
| } | ||
|
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| req := &http.Request{ | ||
| Method: r.Method, | ||
| URL: u, | ||
| } | ||
| req.URL.RawQuery = r.URL.RawQuery | ||
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| resp, err := httpClient.Do(req) | ||
| if err != nil { | ||
| klog.Infof("error from %s: %v", u, err) | ||
| http.Error(w, "internal error", http.StatusBadGateway) | ||
| return | ||
| } | ||
|
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| defer resp.Body.Close() | ||
|
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| w.WriteHeader(resp.StatusCode) | ||
| if _, err := io.Copy(w, resp.Body); err != nil { | ||
| klog.Warningf("error writing response body: %v", err) | ||
| return | ||
| } | ||
|
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| switch resp.StatusCode { | ||
| case 200: | ||
| klog.V(2).Infof("proxied %s %s: %s", r.Method, r.URL, resp.Status) | ||
| default: | ||
| klog.Infof("proxied %s %s: %s", r.Method, r.URL, resp.Status) | ||
| } | ||
| } | ||
|
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| func run() error { | ||
| listen := ":8080" | ||
|
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| clientCert := "" | ||
| clientKey := "" | ||
| caCert := "" | ||
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| flag.StringVar(&clientCert, "client-cert", clientCert, "path to client certificate") | ||
| flag.StringVar(&clientKey, "client-key", clientKey, "path to client key") | ||
| flag.StringVar(&caCert, "ca-cert", caCert, "path to ca certificate") | ||
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| klog.InitFlags(nil) | ||
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| flag.Parse() | ||
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| tlsConfig := &tls.Config{} | ||
|
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| if caCert != "" { | ||
| b, err := ioutil.ReadFile(caCert) | ||
| if err != nil { | ||
| return fmt.Errorf("error reading certificate %q: %v", caCert, err) | ||
| } | ||
| rootCAs := x509.NewCertPool() | ||
| rootCAs.AppendCertsFromPEM(b) | ||
| tlsConfig.RootCAs = rootCAs | ||
| } | ||
|
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| if clientKey != "" { | ||
| keypair, err := tls.LoadX509KeyPair(clientCert, clientKey) | ||
| if err != nil { | ||
| return fmt.Errorf("error reading client keypair: %v", err) | ||
| } | ||
|
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| tlsConfig.Certificates = []tls.Certificate{keypair} | ||
| } | ||
|
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| transport := &http.Transport{ | ||
| TLSClientConfig: tlsConfig, | ||
| } | ||
|
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| s := &healthCheckServer{ | ||
| transport: transport, | ||
| } | ||
|
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| http.HandleFunc("/", s.handler) | ||
|
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| klog.Infof("listening on %s", listen) | ||
|
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| if err := http.ListenAndServe(listen, nil); err != nil { | ||
| return fmt.Errorf("error listening on %q: %v", listen, err) | ||
| } | ||
|
|
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| return fmt.Errorf("unexpected return from ListenAndServe") | ||
| } | ||
|
|
||
| func main() { | ||
| if err := run(); err != nil { | ||
| fmt.Fprintf(os.Stderr, "%v\n", err) | ||
| os.Exit(1) | ||
| } | ||
| } |
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