Kubernetes ConfigMap热更新测试 – 探究ConfigMap的创建和更新流程

ConfigMap热更新测试

ConfigMap是用来存储配置文件的kubernetes资源对象,所有的配置内容都存储在etcd中,下文主要是探究 ConfigMap 的创建和更新流程,以及对 ConfigMap 更新后容器内挂载的内容是否同步更新的测试。

测试示例


假设我们在 default namespace 下有一个名为 nginx-config 的 ConfigMap,可以使用 kubectl命令来获取:

$ kubectl get configmap nginx-config
NAME DATA AGE
nginx-config 1 99d

获取该ConfigMap的内容。

kubectl get configmap nginx-config -o yaml
apiVersion: v1
data:
 nginx.conf: |-
 worker_processes 1;

 events { worker_connections 1024; }

 http {
 sendfile on;

 server {
 listen 80; # a test endpoint that returns http 200s
 location / {
 proxy_pass http://httpstat.us/200;
 proxy_set_header X-Real-IP $remote_addr; } }

 server {

 listen 80;
 server_name api.hello.world;

 location / {
 proxy_pass http://l5d.default.svc.cluster.local;
 proxy_set_header Host $host;
 proxy_set_header Connection "";
 proxy_http_version 1.1;

 more_clear_input_headers 'l5d-ctx-*' 'l5d-dtab' 'l5d-sample'; } }

 server {

 listen 80;
 server_name www.hello.world;

 location / { # allow 'employees' to perform dtab overrides if ($cookie_special_employee_cookie != "letmein") {
 more_clear_input_headers 'l5d-ctx-*' 'l5d-dtab' 'l5d-sample'; } # add a dtab override to get people to our beta, world-v2 set $xheader ""; if ($cookie_special_employee_cookie ~* "dogfood") { set $xheader "/host/world => /srv/world-v2;"; }

 proxy_set_header 'l5d-dtab' $xheader;


 proxy_pass http://l5d.default.svc.cluster.local;
 proxy_set_header Host $host;
 proxy_set_header Connection "";
 proxy_http_version 1.1; } } }
kind: ConfigMap
metadata:
 creationTimestamp: 2017-08-01T06:53:17Z
 name: nginx-config
 namespace: default
 resourceVersion: "14925806"
 selfLink: /api/v1/namespaces/default/configmaps/nginx-config
 uid: 18d70527-7686-11e7-bfbd-8af1e3a7c5bd

ConfigMap中的内容是存储到etcd中的,然后查询etcd:

ETCDCTL_API=3 etcdctl get /registry/configmaps/default/nginx-config
/registry/configmaps/default/nginx-config

注意使用 v3 版本的 etcdctl API,下面是输出结果:

k8s

v1	ConfigMap

T

nginx-configdefault"*$18d70527-7686-11e7-bfbd-8af1e3a7c5bd28B
 �ʀ����xz�


nginx.conf�
 worker_processes 1;

events { worker_connections 1024; }

http {
 sendfile on;

 server {
 listen 80;

 # a test endpoint that returns http 200s
 location / {
 proxy_pass http://httpstat.us/200;
 proxy_set_header X-Real-IP $remote_addr;
 }
 }

 server {

 listen 80;
 server_name api.hello.world;

 location / {
 proxy_pass http://l5d.default.svc.cluster.local;
 proxy_set_header Host $host;
 proxy_set_header Connection "";
 proxy_http_version 1.1;

 more_clear_input_headers 'l5d-ctx-*' 'l5d-dtab' 'l5d-sample';
 }
 }

 server {

 listen 80;
 server_name www.hello.world;

 location / {


 # allow 'employees' to perform dtab overrides
 if ($cookie_special_employee_cookie != "letmein") {
 more_clear_input_headers 'l5d-ctx-*' 'l5d-dtab' 'l5d-sample';
 }

 # add a dtab override to get people to our beta, world-v2
 set $xheader "";

 if ($cookie_special_employee_cookie ~* "dogfood") {
 set $xheader "/host/world => /srv/world-v2;";
 }

 proxy_set_header 'l5d-dtab' $xheader;


 proxy_pass http://l5d.default.svc.cluster.local;
 proxy_set_header Host $host;
 proxy_set_header Connection "";
 proxy_http_version 1.1;
 }
 }
}"

输出中在 nginx.conf 配置文件的基础中增加了文件头内容,是kubernetes增加的。

代码

ConfigMap 结构体的定义:

// ConfigMap holds configuration data for pods to consume.
type ConfigMap struct {
	metav1.TypeMeta `json:",inline"` // Standard object's metadata. // More info: http://releases.k8s.io/HEAD/docs/devel/api-conventions.md#metadata // +optional
	metav1.ObjectMeta `json:"metadata,omitempty" protobuf:"bytes,1,opt,name=metadata"` // Data contains the configuration data. // Each key must be a valid DNS_SUBDOMAIN with an optional leading dot. // +optional Data map[string]string `json:"data,omitempty" protobuf:"bytes,2,rep,name=data"` }

在 staging/src/k8s.io/client-go/kubernetes/typed/core/v1/configmap.go 中ConfigMap 的接口定义:

// ConfigMapInterface has methods to work with ConfigMap resources.
type ConfigMapInterface interface { Create(*v1.ConfigMap) (*v1.ConfigMap, error) Update(*v1.ConfigMap) (*v1.ConfigMap, error) Delete(name string, options *meta_v1.DeleteOptions) error
	DeleteCollection(options *meta_v1.DeleteOptions, listOptions meta_v1.ListOptions) error
	Get(name string, options meta_v1.GetOptions) (*v1.ConfigMap, error) List(opts meta_v1.ListOptions) (*v1.ConfigMapList, error) Watch(opts meta_v1.ListOptions) (watch.Interface, error) Patch(name string, pt types.PatchType, data []byte, subresources ...string) (result *v1.ConfigMap, err error) ConfigMapExpansion }

在 staging/src/k8s.io/client-go/kubernetes/typed/core/v1/configmap.go 中创建 ConfigMap 的方法如下:

// Create takes the representation of a configMap and creates it. Returns the server's representation of the configMap, and an error, if there is any.
func (c *configMaps) Create(configMap *v1.ConfigMap) (result *v1.ConfigMap, err error) {
	result = &v1.ConfigMap{}
	err = c.client.Post(). Namespace(c.ns). Resource("configmaps"). Body(configMap). Do(). Into(result) return }

通过 RESTful 请求在 etcd 中存储 ConfigMap 的配置,该方法中设置了资源对象的 namespace 和 HTTP 请求中的 body,执行后将请求结果保存到 result 中返回给调用者。

注意 Body 的结构

// Body makes the request use obj as the body. Optional. // If obj is a string, try to read a file of that name. // If obj is a []byte, send it directly. // If obj is an io.Reader, use it directly. // If obj is a runtime.Object, marshal it correctly, and set Content-Type header. // If obj is a runtime.Object and nil, do nothing. // Otherwise, set an error. 

创建 ConfigMap RESTful 请求中的的 Body 中包含 ObjectMeta 和 namespace。

HTTP 请求中的结构体:

// Request allows for building up a request to a server in a chained fashion. // Any errors are stored until the end of your call, so you only have to // check once.
type Request struct { // required
	client HTTPClient
	verb string

	baseURL *url.URL
	content ContentConfig
	serializers Serializers // generic components accessible via method setters
	pathPrefix string
	subpath string params url.Values
	headers http.Header // structural elements of the request that are part of the Kubernetes API conventions namespace string
	namespaceSet bool
	resource string
	resourceName string
	subresource string
	timeout time.Duration // output
	err error
	body io.Reader // This is only used for per-request timeouts, deadlines, and cancellations.
	ctx context.Context

	backoffMgr BackoffManager
	throttle flowcontrol.RateLimiter }

测试

分别测试使用 ConfigMap 挂载 Env 和 Volume 的情况。

更新使用ConfigMap挂载的Env

使用下面的配置创建 nginx 容器测试更新 ConfigMap 后容器内的环境变量是否也跟着更新。

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
 name: my-nginx
spec:
 replicas: 1 template:
 metadata:
 labels:
 run: my-nginx
 spec:
 containers: - name: my-nginx
 image: sz-pg-oam-docker-hub-001.tendcloud.com/library/nginx:1.9
 ports: - containerPort: 80
 envFrom: - configMapRef:
 name: env-config
---
apiVersion: v1
kind: ConfigMap
metadata:
 name: env-config
 namespace: default
data:
 log_level: INFO

获取环境变量的值

$ kubectl exec `kubectl get pods -l run=my-nginx -o=name|cut -d "/" -f2` env|grep log_level
log_level=INFO

修改 ConfigMap

$ kubectl edit configmap env-config

修改 log_level 的值为 DEBUG。

再次查看环境变量的值。

$ kubectl exec `kubectl get pods -l run=my-nginx -o=name|cut -d "/" -f2` env|grep log_level
log_level=INFO

实践证明修改 ConfigMap 无法更新容器中已注入的环境变量信息。

更新使用ConfigMap挂载的Volume

使用下面的配置创建 nginx 容器测试更新 ConfigMap 后容器内挂载的文件是否也跟着更新。

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
 name: my-nginx
spec:
 replicas: 1 template:
 metadata:
 labels:
 run: my-nginx
 spec:
 containers: - name: my-nginx
 image: sz-pg-oam-docker-hub-001.tendcloud.com/library/nginx:1.9
 ports: - containerPort: 80
 volumeMounts: - name: config-volume
 mountPath: /etc/config
 volumes: - name: config-volume
 configMap:
 name: special-config
---
apiVersion: v1
kind: ConfigMap
metadata:
 name: special-config
 namespace: default
data:
 log_level: INFO
$ kubectl exec `kubectl get pods -l run=my-nginx -o=name|cut -d "/" -f2` cat /tmp/log_level
INFO

修改 ConfigMap

$ kubectl edit configmap special-config

修改 log_level 的值为 DEBUG。

等待大概10秒钟时间,再次查看环境变量的值。

$ kubectl exec `kubectl get pods -l run=my-nginx -o=name|cut -d "/" -f2` cat /tmp/log_level
DEBUG

我们可以看到使用 ConfigMap 方式挂载的 Volume 的文件中的内容已经变成了 DEBUG。

总结

更新 ConfigMap 后:

  • 使用该 ConfigMap 挂载的 Env 不会同步更新
  • 使用该 ConfigMap 挂载的 Volume 中的数据需要一段时间(实测大概10秒)才能同步更新

ENV 是在容器启动的时候注入的,启动之后 kubernetes 就不会再改变环境变量的值,且同一个 namespace 中的 pod 的环境变量是不断累加的,参考 Kubernetes中的服务发现与docker容器间的环境变量传递源码探究。为了更新容器中使用 ConfigMap 挂载的配置,可以通过滚动更新 pod 的方式来强制重新挂载 ConfigMap,也可以在更新了 ConfigMap 后,先将副本数设置为 0,然后再扩容。

本文转自kubernetes中文社区-Kubernetes ConfigMap热更新测试 – 探究ConfigMap的创建和更新流程

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