Common Dokku Pitfalls

Sunday, 7 December 2014

Dokku is a Docker powered Heroku clone which you can install on your own hardware. I’ve been using it for over a year now and have recently moved all of my sites over to run on it. It doesn’t come without its quirks, see below for more.

1. Insufficient physical memory

runtime: panic before malloc heap initialized
fatal error: runtime: cannot allocate heap metadata

Solution: Configure virtual memory (swap file).

dd if=/dev/zero of=/swapfile bs=1M count=512
mkswap /swapfile
chmod 600 /swapfile

Then add the following to /etc/fstab:

/swapfile         none            swap    sw                0       0

Then run the following to persist it.

swapon -a

2. Python/Ruby app incorrectly detected as Node app

This is down to the presence of a package.json file in your app root.

-----> Building node-js-app ...
Node.js app detected

Solution 1: Set your build pack explicitly to Python (see below). Then install Node.js via dokku-nodejs.

Solution 2: Use heroku-buildpack-multi to set both buildpacks (I haven’t tested this solution).

This way your app will be correctly built as well as your package.json dependencies installed.

3. TLS/SSL config + custom domain plugin incompatibilities

Using plugins such as dokku-domains-plugin or dokku-custom-domains, in combination with Dokku’s TLS support can result in unexpected TLS behaviour (i.e. Some certificates not being applied).

Solution: Use the dokku-nginx-hostname plugin which is compatible with Dokku’s TLS/SSL.

4. BUILDPACK_URL env var not recognised by build

Solution: Create file .env in the root of your app.

Add your build pack to it:

echo "export BUILDPACK_URL=https://github.com/heroku/heroku-buildpack-python" > .env

NOTE: This has been fixed in Dokku >=0.3.9.

5. Cannot deploy static app

buildpack-nginx doesn’t support Dokku >0.3 (Ubuntu 14.04).

Err http://archive.ubuntu.com quantal/main amd64 Packages
  404  Not Found [IP: 91.189.91.15 80]
Err http://archive.ubuntu.com quantal/restricted amd64 Packages
  404  Not Found [IP: 91.189.91.15 80]

W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/quantal-security/main/binary-amd64/Packages  404  Not Found [IP: 91.189.91.15 80]

Solution: Use the following build pack https://github.com/ademuk/buildpack-nginx

See above on how to apply it.