jreisinger/limiting-docker-resources.md

## limiting-docker-resources.md

      
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              limiting-docker-resources.md
            
          
    Limiting a Docker container's memory resource


Terminology


Docker server - the docker command run in daemon mode on a Linux host


Docker image - packaged application with all needed files (libs, configs)
  $ docker pull ...
  $ docker build ...


Docker container - a chrooted process that has been instantiated from a Docker image
  $ docker run ...


Docker and host resources


a container has no resource constraints by default
Docker provides a way to limit memory, CPU and block IO resources
your kernel must support Linux capabilities (docker info | grep WARNING)


Linux and memory resource


if the kernel detects that there is not enough memory, it starts killing processes
any process is subject to killing (including Docker)
a process that uses lot of memory but has not been running for long time is a most likely candidate to get killed (OOM)


Docker and memory resource


Docker adjusts OOM priority in the Docker daemon so it's less likely to get killed
the OOM priority on containers is not adjusted so they are more likely to be killed than the Docker daemon
you should not allow a container to consume too much of the host machine’s memory


Demo - memory limiting

$ git clone git@github.com:jreisinger/mem-muncher.git
$ cd mem-muncher
$ docker build -t mem-muncher .
$ sudo swapoff -a
# in separate terminal tab/window
$ docker stats
$ docker run -it --rm --name mem-muncher mem-muncher
# in separate terminal tab/window
$ docker kill mem-muncher
# limit the memory to 500MB and forbid access to swap
$ docker run -it --rm --name mem-muncher --memory=500m mem-muncher
$ sudo swapon -a 


More

https://docs.docker.com/config/containers/resource_constraints/