How to Set Multiple Commands in One YAML File with Kubernetes

In Kubernetes, you often need to run multiple commands in a single Pod to set up your application environment. This can include tasks like running migrations, copying files, or starting services. In this guide, we'll explore how to define and execute multiple commands within a single YAML file for a Kubernetes Pod.

Prerequisites

Before you begin, you should have:

• Access to a Kubernetes cluster (local or remote)
• kubectl installed and configured
• Basic familiarity with YAML syntax and Kubernetes Pods

Why Run Multiple Commands in a Pod?

Sometimes, your container needs to perform several setup steps before starting the main application. For example, you might want to run a database migration, copy files, or initialize environment variables. Kubernetes lets you define these steps in your Pod's YAML file, but you need to structure your commands correctly.

Using command and args in Kubernetes YAML

Kubernetes lets you override the default container entrypoint using the command and args fields. If you want to run multiple commands, you can use a shell to chain them together.

Example: Chaining Commands with sh -c

Suppose you want your container to print a message, create a file, and then start a web server. You can do this by chaining commands with && inside a shell.

apiVersion: v1
kind: Pod
metadata:
  name: multi-command-demo
spec:
  containers:
    - name: busybox
      image: busybox
      command: ['sh', '-c']
      args:
        - |
          echo "Starting setup..." && \
          touch /tmp/initialized && \
          httpd -f -p 8080

What this does:

• Runs a shell (sh -c) so you can use shell features like && and multi-line commands.
• Prints a message, creates a file, and starts the httpd server in one go.

Why Use sh -c?

The sh -c pattern lets you write complex logic, use environment variables, and handle errors. If any command fails, the container will exit unless you add error handling.

Example: Using a Script for Complex Logic

For more advanced setups, it's often cleaner to use a script. You can bake the script into your container image or mount it as a ConfigMap.

apiVersion: v1
kind: Pod
metadata:
  name: script-demo
spec:
  containers:
    - name: app
      image: alpine
      command: ['sh', '/app/startup.sh']
      volumeMounts:
        - name: script-volume
          mountPath: /app
  volumes:
    - name: script-volume
      configMap:
        name: startup-script
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: startup-script
  namespace: default
data:
  startup.sh: |
    #!/bin/sh
    echo "Running migrations..."
    ./migrate-db.sh
    echo "Starting app..."
    ./run-app.sh

What this does:

• Mounts a script from a ConfigMap into the container.
• The script can run as many commands as you need, with full shell scripting features.

This can be visualized as follows:

+-------------------+
|   Pod Startup     |
+-------------------+
          |
          v
+-------------------+
|  sh -c "cmd1 &&   |
|   cmd2 && cmd3"   |
+-------------------+
          |
          v
+-------------------+
|  Container Ready  |
+-------------------+

Tips for Multi-Command Pods

• Use && to stop on the first error, or ; to run all commands regardless of errors.
• For readability, use multi-line YAML strings with |.
• For complex setups, prefer scripts over long inline commands.
• Make sure your container image includes the shell you want to use (e.g., sh, bash).

Next Steps

You can expand on this by using Kubernetes Init Containers for pre-start tasks, or by orchestrating more advanced workflows with Jobs and CronJobs. Try experimenting with different shell scripting techniques to make your container startup logic robust and maintainable.