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使用`kubectl exec`在容器中执行命令行

Developers can use kubectl exec to run commands in a container. This guide demonstrates two use cases.

Using kubectl exec to check the environment variables of a container

Kubernetes exposes services through environment variables. It is convenient to check these environment variables using kubectl exec.

We first create a pod and a service,

$ kubectl create -f examples/guestbook/redis-master-controller.yaml
$ kubectl create -f examples/guestbook/redis-master-service.yaml

wait until the pod is Running and Ready,

$ kubectl get pod
NAME                 READY     REASON       RESTARTS   AGE
redis-master-ft9ex   1/1       Running      0          12s

then we can check the environment variables of the pod,

$ kubectl exec redis-master-ft9ex env
...
REDIS_MASTER_SERVICE_PORT=6379
REDIS_MASTER_SERVICE_HOST=10.0.0.219
...

We can use these environment variables in applications to find the service.

Using kubectl exec to check the mounted volumes

It is convenient to use kubectl exec to check if the volumes are mounted as expected. We first create a Pod with a volume mounted at /data/redis,

kubectl create -f docs/user-guide/walkthrough/pod-redis.yaml

wait until the pod is Running and Ready,

$ kubectl get pods
NAME      READY     REASON    RESTARTS   AGE
storage   1/1       Running   0          1m

we then use kubectl exec to verify that the volume is mounted at /data/redis,

$ kubectl exec storage ls /data
redis

Using kubectl exec to open a bash terminal in a pod

After all, open a terminal in a pod is the most direct way to introspect the pod. Assuming the pod/storage is still running, run

$ kubectl exec -ti storage -- bash
root@storage:/data#

This gets you a terminal.