Prevent Your Container Apps From Running As Root

In case you missed it, we had a special YouTube Live Thursday to talk about Docker selling their Enterprise business to Mirantis.

Today we’re back on schedule with my next security recommendation for using Docker. The past few newsletters have covered Docker Security. Today’s topic is about the USER command in a Dockerfile, and how it can be used to ensure your containerized app isn’t running as root in the container.

When a container runs an instance of an image, unless otherwise specified, the application is running as root inside the container. I’m sure you’ve been told that your apps shouldn’t run as root, and that’s still true in containers.

Following the principle of least privilege, we should strive to grant only the minimum requirements to run the application. This principle is not related to Docker, but general to IT security as a whole.

I covered an example of this in my YouTube Live stream with the node image. Many language images have a “useradd” command included in a RUN command, but never actually specify the USER stanza to switch from the root user to this new custom user.

Note this is all already done for us in Official repos that run an app, like Nginx, MySQL, etc.

It’s NOT enabled with the USER command in programming language Official images, like Node.js, Python, etc. You’ll need to add USER <username> yourself for those, depending on if you app works as a non-root user.

NOTE: In order to make sure the new user can run the app, you might need to include some additional chown commands to give permissions to the new user.

Thanks for reading,

–Bret

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