Setting memory and CPU limits on Docker in Ubuntu

I've been hunting down a problem this morning that keeps causing my laptop to totally lock up. I suspected it was related to Docker because it happened every time I hit a particular endpoint on a local webserver running in Docker.

When I was running Docker on a MBP, I could easily limit the total resources Docker used through a program that lived in the taskbar. I found it more challenging on Ubuntu but after some poking around, I found an question on StackOverflow by user Leltir that gave me the answer. I have modified the answer by adding comments and adding my particular limits

  1. Create a file in /etc/systemd/system/docker_limit.slice with the following contents:

    Description=Slice that limits docker resources
    # Turn on CPU limit
    # Set CPU limit to use 400% of total CPU resources
    # I have 8 cores so this limits Docker to using 4 of them
    # Turn on memory limit
    # Set memory limit to 8GB
  2. Run the following to load the new system file and start it:

    sudo systemctl daemon-reload
    sudo systemctl start docker_limit.slice
  3. Add the following to /etc/docker/daemon.json (merging it into any existing JSON in that file):

    {"cgroup-parent": "/docker_limit.slice"}
  4. Restart docker with sudo systemctl restart docker

For help with what limits can be set in the system file, see the RedHat doc “Modifying Control Groups”