How to upgrade docker container after its image changed

Question

Let's say I have pulled the official mysql:5.6.21 image.

I have deployed this image by creating several docker containers.

These containers have been running for some time until MySQL 5.6.22 is released. The official image of mysql:5.6 gets updated with the new release, but my containers still run 5.6.21.

How do I propagate the changes in the image (i.e. upgrade MySQL distro) to all my existing containers? What is the proper Docker way of doing this?

Answer 1

After evaluating the answers and studying the topic I'd like to summarize.

The Docker way to upgrade containers seems to be the following:

Application containers should not store application data. This way you can replace app container with its newer version at any time by executing something like this:

docker pull mysql
docker stop my-mysql-container
docker rm my-mysql-container
docker run --name=my-mysql-container --restart=always 
  -e MYSQL_ROOT_PASSWORD=mypwd -v /my/data/dir:/var/lib/mysql -d mysql

You can store data either on host (in directory mounted as volume) or in special data-only container(s). Read more about it

• About volumes (Docker docs)
• Tiny Docker Pieces, Loosely Joined (by Tom Offermann)
• How to deal with persistent storage (e.g. databases) in Docker (Stack Overflow question)

Upgrading applications (eg. with yum/apt-get upgrade) within containers is considered to be an anti-pattern. Application containers are supposed to be immutable, which shall guarantee reproducible behavior. Some official application images (mysql:5.6 in particular) are not even designed to self-update (apt-get upgrade won't work).

I'd like to thank everybody who gave their answers, so we could see all different approaches.