Kubernetes

Using Kubectl Exec : Connect to Your Kubernetes Containers

Connect to containers using Kubectl Exec

In this article, we will look at the kubectl exec command to show how to get a shell into a running container in your Kubernetes (K8S) cluster and how to run individual commands on a container with some useful examples.

Example Setup

To get a shell to your container, first, find its name.

And to have all the commands in one place check out our Kubernetes Cheat Sheet with 15 Kubectl Commands & Objects.

kubectl get pods

Note that in order to get a shell, your container image has to have that shell available.

I have one running on my Azure Kubernetes Service (AKS) cluster called aks-helloworld-one-56c7b8d79d-lkz6s, which we will use for these examples. This uses the Hello world image, which is a simple Node.js web application used in Azure Container Instances for the examples on docs.microsoft.com.

This container is controlled by a deployment called aks-helloworld-one.

kubectl get deployments
kubectl exec - get deployments

My aks-helloworld-one.yaml deployment file looks like this:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: aks-helloworld-one
spec:
  replicas: 1
  selector:
    matchLabels:
      app: aks-helloworld-one
  template:
    metadata:
      labels:
        app: aks-helloworld-one
    spec:
      containers:
      - name: aks-helloworld-one
        image: mcr.microsoft.com/azuredocs/aks-helloworld:v1
        ports:
        - containerPort: 80
        env:
        - name: TITLE
          value: "Welcome to Azure Kubernetes Service (AKS)"
---
apiVersion: v1
kind: Service
metadata:
  name: aks-helloworld-one
spec:
  type: ClusterIP
  ports:
  - port: 80
  selector:
    app: aks-helloworld-one

If you are following along, you can create the file above and use the command below to deploy the container on your cluster:

kubectl create deployment aks-helloworld-one.yaml

Connect to Your Container

To get a bash shell into the running container:

kubectl exec --stdin --tty aks-helloworld-one-56c7b8d79d-xqx5t -- /bin/bash
  • The double dash (--) separates the arguments you want to pass to the command from the kubectlarguments.
  • /bin/bash is the type of shell you want (it could also be /bin/sh for example).
  • The--stdinoption passes the stdin (or standard input) to the container. Use -i for short.
  • The --tty Stdin is a TTY. Use -t for short.
  • You can also specify the --quiet or -q option to disable all output from kubectlitself. You’ll only see output produced by the process running in the container.
  • You can also specify the length of time to wait until at least one pod is running, the default being 1m using -pod-runnning-timeout. This is specified as the length of time (like 5s, 2m, or 3h, higher than zero), e.g. --pod-running-timeout=2m .

Once inside the container, you can run commands directly, e.g. ls to list the contents of the directory.

kubectl exec - ls inside container

Or ps aux to view the running processes:

Once you are finished in the container, type exit to return to your console shell.

Running Single Commands in a Container

You can also run single commands directly using kubectl exec. Some useful examples are shown below:

  • Get the time and date
kubectl exec <pod name> -- date
kubectl exec pod name - date
  • List the running environment variables
kubectl exec <pod name> -- env
kubectl exec pod name - env
  • Update packages
kubectl exec <pod name> -- apt-get update
  • View the mount points
kubectl exec shell-demo -- cat /proc/1/mounts

Connect to a Specified Container When a Pod Has More Than One Container

If a Pod has more than one container, use --container or -c to specify a container in the kubectl exec command.

kubectl exec -i -t <pod name> --container <container name> -- /bin/bash

Key Points

You can connect to a running container using kubectl exec and also use it to execute single commands. Connecting to a container is useful to view logs, inspect processes, mount points, environment variables, and package versions, amongst other things.

kubectl exec will give you full shell access to the container, so modifying it and installing packages that are not part of the container image is possible but is not recommended unless for temporary troubleshooting purposes. If extra modifications or packages are required permanently for the container, the image should be modified, and the new version should be deployed to maintain immutability and reproducibility.

Spacelift helps you manage the complexities and compliance challenges of using Kubernetes. Anything that can be run via kubectl can be run within a Spacelift stack. Find out more about how Spacelift works with Kubernetes, and get started on your journey by creating a free trial account.

Cheers!

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