研发工程师玩转Kubernetes——创建一个测试容器
测试容器并不是什么都没有的容器，只是它没有我们期望的常驻进程。我们常用它来做一些测试。
举个例子，在《研发工程师玩转Kubernetes——自动扩缩容》中我们使用本地wrk进行了压力测试。如果我们希望进入容器手工调用wrk，该怎么做呢？
错误的案例
虽然下面这个清单文件的镜像中包含了wrk程序，但是它没有启动一个常驻进程。导致运行这个Pod一直会报错“Back-off restarting failed container”，Reason是CrashLoopBackOff。
apiVersion: v1
kind: Pod
metadata:
name: wrk
labels:
name: wrk
spec:
containers:
- name: wrk-container
image: localhost:32000/wrk:v1kubectl describe pod wrkName: wrk
Namespace: default
Priority: 0
Service Account: default
Node: fangliang-virtual-machine/192.168.137.248
Start Time: Mon, 29 May 2023 14:30:37 +0800
Labels: name=wrk
Annotations: cni.projectcalico.org/containerID: 75a18bfd3f3d83dd14b7bc9655343842d9bac20a4c52a7ee75932013be395e01
cni.projectcalico.org/podIP: 10.1.62.178/32
cni.projectcalico.org/podIPs: 10.1.62.178/32
Status: Running
IP: 10.1.62.178
IPs:
IP: 10.1.62.178
Containers:
wrk-container:
Container ID: containerd://80d5186f701de4ccd861dc84078290250f3452a90ed226cb246a4f6b9aab5ef6
Image: localhost:32000/wrk:v1
Image ID: localhost:32000/wrk@sha256:3548119fa498e871ac75ab3cefb901bf5a069349dc4b1b92afab8db4653f6b25
Port: <none>
Host Port: <none>
State: Waiting
Reason: CrashLoopBackOff
Last State: Terminated
Reason: Completed
Exit Code: 0
Started: Mon, 29 May 2023 14:31:17 +0800
Finished: Mon, 29 May 2023 14:31:17 +0800
Ready: False
Restart Count: 3
Environment: <none>
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-ld6j6 (ro)
Conditions:
Type Status
Initialized True
Ready False
ContainersReady False
PodScheduled True
Volumes:
kube-api-access-ld6j6:
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 54s default-scheduler Successfully assigned default/wrk to fangliang-virtual-machine
Normal Pulled 14s (x4 over 53s) kubelet Container image "localhost:32000/wrk:v1" already present on machine
Normal Created 14s (x4 over 53s) kubelet Created container wrk-container
Normal Started 14s (x4 over 53s) kubelet Started container wrk-container
Warning BackOff 2s (x6 over 52s) kubelet Back-off restarting failed container wrk-container in pod wrk_default(588fb4f3-d649-4570-b64c-a4eff748417d)正确的案例
我们只要启动一个常驻进程就可以解决这个问题。
在linux系统中，/dev/null是一个非常特殊的文件，它会抛弃所有写入其中的数据。于是我们持续查看这个文件的写入，就可以制造一个常驻进程，而且没有其他额外的影响。
command: “/bin/bash”, “-ce”, “tail -f /dev/null”
即把清单文件改成如下
# wrk_pod.yaml
apiVersion: v1
kind: Pod
metadata:
name: wrk
labels:
name: wrk
spec:
containers:
- name: wrk-container
image: localhost:32000/wrk:v1
command: ["/bin/bash", "-ce", "tail -f /dev/null"]测试
创建Pod
kubectl create -f wrk_pod.yamlpod/wrk created
登录容器
kubectl exec wrk -c wrk-container -it /bin/bash执行指令
wrk -t10 -c10 -d10 http://192.168.137.248:30000
可见，我们已经可以在这个测试容器中执行我们想执行的指令了。
参考资料
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原始发表：2023-05-30，如有侵权请联系 cloudcommunity@tencent.com 删除
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