Docker compose and entropy

Photo by Markus Spiske on Unsplash

Ran into a seemingly commonplace problem (my docker-compose was hanging randomly) with an extremely unexpected answer (my system was running out of entropy)!

TL;DR: install haveged on your system

What is entropy? It’s basically the “randomness” on your machine from your interactions with it (keyboard, mouse, hard drive activity, web activity). Entropy is used in security applications such as SSH, PGP, SSL/TLS and random number generators.

So how does this affect docker-compose? According to this thread, one of the docker-compose dependencies makes a call out to /dev/random and a machine that doesn’t have enough entropy will block docker-compose. After a fixed amount of time, that docker-compose dependency gives up waiting for /dev/random and polls /dev/urandom instead which is less secure (less random, but also non-blocking).

Generally if you’re on a bare metal, entropy won’t be a problem. But in a VPS environment where there are no keyboard/mouse interactions and the hard drives are virtualized (less random), entropy can get low.

You can check the entropy of your system by using:

cat /proc/sys/kernel/random/entropy_avail

Generally, the larger the better, and anything over 1000 is “good enough”.

If your entropy is too low, you can install haveged :

apt-get install haveged

What is haveged and how does it work? To the best of my understanding, it is similar to how /dev/random generate entropy bits, but adds in more sources of information, such as CPU clock cycle timing and cache misses. A very interesting read on this can be found here.




Tech junkie, entrepreneur dreamer, practical engineer

Love podcasts or audiobooks? Learn on the go with our new app.

Recommended from Medium

Login and Registration Form In Bootstrap 4

Improved decoder reuse in ExoPlayer

How Ford Motor Company adopts Kubernetes and Red Hat Openshift?

Project Valhalla: fast and furious Java

Scaling Search by Sharding at Blibli

App Development: Grasping Functional and Non-Functional Requirements

Easy Way to Manage HREFLANG Tags on Blogs

Java 9 features

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store
Albert Liang

Albert Liang

Tech junkie, entrepreneur dreamer, practical engineer

More from Medium

The exponentially zero valuation of IPython — or, why valuing software is so hard.

Deploying Machine Learning models with TensorFlow Serving — an introduction

Tutorial: execute code in a remote machine using the ClearML queue

High Performance Computing