一、初始化容器简介与应用场景
1.1 初始化容器简介
初始化容器是在pod的主容器启动之前要运行的容器，主要是做一些主容器的前置工作，它有两大特征：
- 1、初始化容器必须运行完成直到结束，若某初始化容器运行失败，那么kubernetes需要重启它直到成功完成
- 2、初始化容器必须按照定义的顺序执行，当且仅当前一个成功之后，后一个才能执行
1.2 初始化容器使用场景
初始化容器有很多应用场景，如下为最常见的几个：
- 提供主容器镜像中不具备的工具程序或者自定义代码
- 初始化容器要先于应用容器串行启动并运行完成，因此可用于延后应用容器的启动直至其依赖的条件得到满足
二、创建初始化容器
2.1 编写yaml文件
如下，编写pod_init_container.yaml文件，内容如下，设置一个初始化容器，用于ping 192.168.16.41，如果ping通了则继续，如果ping不通，则继续等待直到ping通
apiVersion: v1
kind: Namespace
metadata:
name: dev
---
apiVersion: v1
kind: Pod
metadata:
name: pod-init-container
namespace: dev
labels:
user: redrose2100
spec:
containers:
- name: nginx
image: nginx:1.17.1
ports:
- name: nginx-port
containerPort: 80
protocol: TCP
initContainers:
- name: test-ping
image: busybox:1.30
command: ["sh","-c","until ping 192.168.16.41 -c 1 ; do echo 'waiting for ping...'; sleep 2; done;"]
2.2 创建资源
使用如下命令创建资源
[root@master pod]# kubectl apply -f pod_init_container.yaml
namespace/dev created
pod/pod-init-container created
[root@master pod]#
2.3 查看资源创建状态
如下，可以看到pod创建过程中，首先创建并执行的初始化容器
[root@master pod]# kubectl get pod -n dev
NAME READY STATUS RESTARTS AGE
pod-init-container 1/1 Running 0 2m15s
[root@master pod]# kubectl describe pod pod-init-container -n dev
Name: pod-init-container
Namespace: dev
Priority: 0
Node: node2/192.168.16.42
Start Time: Tue, 22 Mar 2022 17:02:15 +0800
Labels: user=redrose2100
Annotations: <none>
Status: Running
IP: 10.244.2.37
IPs:
IP: 10.244.2.37
Init Containers:
test-ping:
Container ID: docker://ad5638803015fa3aec476117828a68561c3b11e478e3ea50c036700871a6e318
Image: busybox:1.30
Image ID: docker-pullable://busybox@sha256:4b6ad3a68d34da29bf7c8ccb5d355ba8b4babcad1f99798204e7abb43e54ee3d
Port: <none>
Host Port: <none>
Command:
sh
-c
until ping 192.168.16.41 -c 1 ; do echo 'waiting for ping...'; sleep 2; done;
State: Terminated
Reason: Completed
Exit Code: 0
Started: Tue, 22 Mar 2022 17:02:15 +0800
Finished: Tue, 22 Mar 2022 17:02:15 +0800
Ready: True
Restart Count: 0
Environment: <none>
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-z8w87 (ro)
Containers:
nginx:
Container ID: docker://e1f0e2f09720dcd0f467288e8984b7741f2e6d73825428e50c9b025779a307cc
Image: nginx:1.17.1
Image ID: docker-pullable://nginx@sha256:b4b9b3eee194703fc2fa8afa5b7510c77ae70cfba567af1376a573a967c03dbb
Port: 80/TCP
Host Port: 0/TCP
State: Running
Started: Tue, 22 Mar 2022 17:02:16 +0800
Ready: True
Restart Count: 0
Environment: <none>
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-z8w87 (ro)
Conditions:
Type Status
Initialized True
Ready True
ContainersReady True
PodScheduled True
Volumes:
kube-api-access-z8w87:
Type: Projected (a volume that contains injected data from multiple sources)
TokenExpirationSeconds: 3607
ConfigMapName: kube-root-ca.crt
ConfigMapOptional: <nil>
DownwardAPI: true
QoS Class: BestEffort
Node-Selectors: <none>
Tolerations: node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 2m29s default-scheduler Successfully assigned dev/pod-init-container to node2
Normal Pulled 2m29s kubelet Container image "busybox:1.30" already present on machine
Normal Created 2m29s kubelet Created container test-ping
Normal Started 2m29s kubelet Started container test-ping
Normal Pulled 2m28s kubelet Container image "nginx:1.17.1" already present on machine
Normal Created 2m28s kubelet Created container nginx
Normal Started 2m28s kubelet Started container nginx
[root@master pod]#
2.4 删除资源
使用如下命令删除资源
[root@master pod]# kubectl delete -f pod_init_container.yaml
namespace "dev" deleted
pod "pod-init-container" deleted
[root@master pod]#
