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docker-preoomkiller

Watches container memory use and softly kills the container with SIGTERM before Docker OOMKills it

Dependencies

Python 2 / 3

preoomkiller has no Python package dependencies so should work everywhere

Install

With curl: put RUN curl -sSf https://raw.githubusercontent.com/izakp/docker-preoomkiller/master/install-preoomkiller.sh | sh in your Dockerfile to install preoomkiller to /usr/local/bin

Manually ADD preoomkiller to your Docker image somewhere on your $PATH

Use

By default, preoomkiller will send SIGTERM to its parent pid, and is designed to run in the background in a container's entrypoint script.

For example use, see the Dockerfiles and docker-entrypoint.sh in the root of this repo. preoomkiller is invoked with exec /usr/local/bin/preoomkiller & before the main process executes in the foreground, and so the resulting process tree will look like:

root         1  0.1  0.0   4036   664 ?        Ss   14:24   0:00 /usr/bin/dumb-init -- /docker-entrypoint.sh
root         8  0.0  0.0  19708  3196 ?        Ss   14:24   0:00 /bin/bash /docker-entrypoint.sh
root         9  0.0  0.0  24512  6400 ?        S    14:24   0:00  \_ python /usr/local/bin/preoomkiller
root        36  0.0  0.0   5932   644 ?        S    14:24   0:00  \_ sleep 1

You can also configure preoomkiller to send its signal to pid 1 (see below)

preoomkiller is observed to use approximately 3.4Mb running on Python 2 and 5.7Mb running on Python 3

Configuration options

preoomkiller won't start unless the environment variable ENABLE_PREOOMKILLER is set

PREOOMKILLER_MEMORY_USE_FACTOR - (float) at what percentage of used / total memory to kill the container (default 0.95)

PREOOMKILLER_POLL_INTERNAL (integer) - how many seconds to wait beween polling memory use (default 10)

PREOOMKILLER_KILL_SIGNAL (integer) - what signal to send to the process (default SIGTERM / 15)

PREOOMKILLER_KILL_PID (integer) - what pid will receive a SIGTERM (default: the pid of the parent that spawned preoomkiller) If you don't start preoomkiller and your application's main process via an entrypoint script (see the example docker-entrypoint.sh) you can also set this to 1. Note: make sure you're using an init system like dumb-init to make sure the pid 1 process properly proxies signals to children

PREOOMKILLER_DEBUG - if set, print memory statistics when polling

Testing

make test-all

Building Docker images

make build-all