k8s-init容器学习

1. 什么是Init容器

Init容器会在业务容器启动之前运行一些初始化动作，Pod可以包含一个或者多个Init容器，只有所有的Init容器运行成功后，业务容器才会运行，如果期间有Init容器运行失败，kubelet 会不断地重启该 Init 容器直到该容器成功为止，如果Pod 对应的 restartPolicy 值为 “Never”，并且 Pod 的 Init 容器失败， 则 Kubernetes 会将整个 Pod 状态设置为失败。

2. Init容器和普通容器有什么区别

Init容器不支持lifecycle，livenessProbe，startupProbe，readinessProbe这些粗活就绪探针，因为Init容器完成任务就退出了。

3. 同时存在Init和业务容器Pod资源如何申请

如下场景，下面只包含内存一种资源

spec:# Init容器：按顺序执行，全部完成后才启动业务容器initContainers:- name: init-container-aimage: busybox:1.35command: ["/bin/sh", "-c", "echo 'Init Container A running'; sleep 10"]  # 模拟初始化操作resources:requests:memory: "20M"  # 申请20M内存limits:memory: "100M"  # 限制最大使用100M内存- name: init-container-bimage: busybox:1.35command: ["/bin/sh", "-c", "echo 'Init Container B running'; sleep 15"]  # 模拟初始化操作resources:requests:memory: "100M"  # 申请100M内存limits:memory: "200M"  # 限制最大使用200M内存# 业务容器：并行启动containers:- name: app-container-aimage: nginx:alpineports:- containerPort: 80resources:requests:memory: "2G"  # 申请2G内存limits:memory: "8G"  # 限制最大使用8G内存- name: app-container-bimage: redis:alpineports:- containerPort: 6379resources:requests:memory: "1G"  # 申请1G内存limits:memory: "2G"  # 限制最大使用2G内存# 重启策略：默认Always，Init容器失败会自动重启restartPolicy: Always

资源申请如下:

init-container-a： 
request.memory: 20M
limits.memory: 100Minit-container-b：
request.memory: 100M
limits.memory: 200Mapp-container-a：
request.memory: 2G
limits.memory: 8Gapp-container-b：
request.memory: 1G
limits.memory: 2G

Pod申请资源原理：取Init或者业务容器limit 或 request 的最大值，下面计算一下：

Init是串行，所以资源不需要累加：
request.memory: 100M
limits.memory: 200M
如上是Init所需的最大request和limits

业务容器是并行的，所以资源需要累加：
request.memory: 3G
limits.memory: 10G

Pod在申请资源时一定要保证Init容器可以正常运行，所以Init和业务容器谁的request，limits大就按照谁的资源申请配置取申请资源。

4. 创建Init容器

下面将创建一个卷，使用Init容器将业务容器nginx的index文件修改掉

nginx-po.yaml:

apiVersion: v1
kind: Pod
metadata:name: nginx
spec:containers:- name: nginximage: nginximagePullPolicy: IfNotPresentports:- containerPort: 80volumeMounts:- name: htmlmountPath: /usr/share/nginx/htmlresources:requests:cpu: "50M"memory: "64Mi"limits:cpu: "100m"memory: "128Mi"# 通过initContainers创建Init容器，和普通容器创建一样，Init容器名和业务容器名必须唯一。initContainers:- name: installimage: busybox:1.28imagePullPolicy: IfNotPresentcommand:- /bin/sh- -c- |echo "This is an experimental test of the Init container." > /usr/share/nginx/html/index.htmlvolumeMounts:- name: htmlmountPath: "/usr/share/nginx/html"resources:requests:cpu: "10m"memory: "16Mi"limits:cpu: "20m"memory: "32Mi"volumes:- name: htmlemptyDir: {}

kubectl apply -f nginx-po.yaml

查看Pod状态：

kubectl get pod

NAME    READY   STATUS     RESTARTS   AGE
nginx   0/1     Init:0/1   0          29s

可以看出有一个Init容器正在执行，查看一下事件：

kubectl describe pod nginx

Events:Type    Reason     Age    From               Message----    ------     ----   ----               -------Normal  Scheduled  2m58s  default-scheduler  Successfully assigned default/nginx to k8s-node01Normal  Pulling    2m23s  kubelet            Pulling image "busybox:1.28"Normal  Pulled     99s    kubelet            Successfully pulled image "busybox:1.28" in 44.089s (44.089s including waiting). Image size: 1146369 bytes.Normal  Created    99s    kubelet            Created container: installNormal  Started    99s    kubelet            Started container installNormal  Pulling    98s    kubelet            Pulling image "nginx"Normal  Pulled     95s    kubelet            Successfully pulled image "nginx" in 2.763s (2.763s including waiting). Image size: 192385289 bytes.Normal  Created    95s    kubelet            Created container: nginxNormal  Started    95s    kubelet            Started container nginx

查看Init容器状态

kubectl describe pod nginx

Init Containers:install:Container ID:  docker://0f6b2f03b7820a7c7358d64f97bf8e3ae018cb993f21868cddff57515a1f0527Image:         busybox:1.28Image ID:      docker-pullable://busybox@sha256:141c253bc4c3fd0a201d32dc1f493bcf3fff003b6df416dea4f41046e0f37d47Port:          <none>Host Port:     <none>Command:/bin/sh-cecho "This is an experimental test of the Init container." > /usr/share/nginx/html/index.htmlState:          TerminatedReason:       CompletedExit Code:    0Started:      Fri, 12 Sep 2025 09:10:40 +0800Finished:     Fri, 12 Sep 2025 09:10:41 +0800Ready:          TrueRestart Count:  0Limits:cpu:     20mmemory:  32MiRequests:cpu:        10mmemory:     16MiEnvironment:  <none>Mounts:/usr/share/nginx/html from html (rw)/var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-4lzl2 (ro)

通过字段State下的Reason和Exit Code可以看出Init容器已经完成退出了，且返回值为0。