How to use kubectl run command to set environment variables for a container?

Using kubectl run to Set Environment Variables for a Container

In Kubernetes, the kubectl run command is a convenient way to quickly create a deployment or a pod with a single command. One of the useful features of kubectl run is the ability to set environment variables for the container(s) within the created pod.

Setting Environment Variables with kubectl run

To set environment variables for a container using kubectl run, you can use the --env flag followed by the key-value pair of the environment variable. Here's the basic syntax:

kubectl run <pod-name> --image=<image-name> --env="<key>=<value>"

For example, let's say you want to create a pod named my-app using the nginx:latest image, and set the APP_ENV environment variable to production. You can use the following command:

kubectl run my-app --image=nginx:latest --env="APP_ENV=production"

This will create a pod with the nginx:latest image, and the APP_ENV environment variable will be set to production for the container.

You can also set multiple environment variables by repeating the --env flag:

kubectl run my-app --image=nginx:latest --env="APP_ENV=production" --env="LOG_LEVEL=info"

This will set both the APP_ENV and LOG_LEVEL environment variables for the container.

Using Environment Variables in Kubernetes Manifests

While kubectl run is a convenient way to quickly create a pod with environment variables, in a production environment, you'll typically want to use Kubernetes manifests (YAML files) to define your deployments, services, and other resources. In this case, you can define environment variables in the container specification of your Kubernetes manifest.

Here's an example Kubernetes deployment manifest that sets the APP_ENV and LOG_LEVEL environment variables:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
      - name: my-app
        image: nginx:latest
        env:
        - name: APP_ENV
          value: production
        - name: LOG_LEVEL
          value: info

In this example, the environment variables are defined in the env section of the container specification. This approach allows you to manage your Kubernetes resources more effectively, as you can version control the manifest file and apply it to your cluster using kubectl apply -f <manifest-file.yaml>.

Visualizing the Kubernetes Deployment Workflow

Here's a Mermaid diagram that illustrates the workflow of creating a Kubernetes deployment with environment variables:

This diagram shows the steps involved in creating a Kubernetes deployment with environment variables, from the developer writing the manifest to the final deployment of the container with the specified environment variables.

In summary, the kubectl run command provides a convenient way to quickly create a pod with environment variables, while using Kubernetes manifests allows for more robust and maintainable configuration of your applications in a production environment.