Solved: How to cap or limit memory usage of a docker container

In this post we will see how we can cap or restrict the maximum amount of memory the container can use.
Let’s first see the current usage of container id ec6ed4af7c34 with “docker stats”.

docker stats ec6ed4af7c34

In the below image we can see the current limit of the container is 300MiB

Now let’s change this limit to 200MiB of a running container.

docker container update -m 200m ec6ed4af7c34

Now when we look at “docker stats” we can see in the image below the new limit on the container.

If you want to set the memory limit at the time of launching the container itself do it as

docker run -exec -it -m 200m image-name /bin/bash

Compose file version 3
If you want to restrict the usage from the compose file itself you can follow below example, the redis service is constrained to use no more than 50M of memory and 0.50 (50%) of available processing time (CPU), and has 20M of memory and 0.25 CPU time reserved (as always available to it).

version: '3'
services:
  redis:
    image: redis:alpine
    deploy:
      resources:
        limits:
          cpus: '0.50'
          memory: 50M
        reservations:
          cpus: '0.10'
          memory: 20M

Hope this post is helpful to you. Do let me know if you have any query.