How to Upgrade a Docker Container After Its Image Changed

TLDR

To upgrade a Docker container after its image has changed, pull the updated image, stop the running container, and recreate it using the new image. Use docker-compose or orchestration tools like Kubernetes for seamless upgrades.

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When working with Docker containers, you may need to upgrade a container to use a new version of its image. This guide will show you how to upgrade a Docker container after its image has changed, ensuring minimal downtime and smooth transitions.

Step 0: Use a volume for Persistent Data

Before upgrading a container, make sure that any persistent data is stored in a Docker volume or bind mount. This ensures that your data remains intact during the upgrade process. If you haven't set up a volume yet, you can do so with the following command:

docker volume create <volume-name>

Then, when you run your container, use the -v flag to mount the volume:

docker run -d --name <container-name> -v <volume-name>:/data <image-name>:<tag>

Note that if you don't use a volume, any data stored in the container's filesystem will be lost when you remove the container.

Step 1: Pull the Updated Image

Start by pulling the updated version of the image from the registry:

docker pull <image-name>:<new-tag>

Replace <image-name> and <new-tag> with the name and tag of the updated image. For example:

docker pull nginx:1.21

This command downloads the new version of the image to your local system.

Step 2: Stop the Running Container

Stop the container that is using the old image:

docker stop <container-name>

Replace <container-name> with the name or ID of the container. For example:

docker stop my-nginx

Step 3: Remove the Old Container

Remove the stopped container to free up the name for the new container:

docker rm <container-name>

For example:

docker rm my-nginx

Step 4: Create a New Container with the Updated Image

Start a new container using the updated image:

docker run -d --name <container-name> <image-name>:<new-tag>

For example:

docker run -d --name my-nginx nginx:1.21

This creates a new container with the updated image.

Step 5: Verify the Upgrade

Check that the new container is running and using the updated image:

docker ps

You should see the new container in the list.

Using Docker Compose for Upgrades

If you are using Docker Compose, upgrading a container is even easier. Update the image tag in the docker-compose.yml file:

version: '3.8'
services:
  web:
    image: nginx:1.21
    ports:
      - '8080:80'

Then run the following command to recreate the container:

docker-compose up -d

Docker Compose will pull the updated image and recreate the container.

Additional Tips

• Automate Upgrades: Use CI/CD pipelines to automate image updates and container upgrades.

• Minimize Downtime: Use rolling updates or load balancers to minimize downtime during upgrades.

• Monitor Logs: Check container logs to ensure the new container is running correctly:

  docker logs <container-name>
  

By following these steps, you can efficiently upgrade Docker containers to use new images while maintaining stability and minimizing downtime.