Dockero in the Local Development Environment

I’ve been using the excellent Dockero library for running some Docker containers in my web applications. In production environments the applications are running on the actual Docker runtime, but in my development environment I like to use alternatives.

Specifically, when I started using macOS again recently, I first opted for Colima for its simplicity. However, anything involving Docker in my local development environment broke, and it took me a while to figure out what was wrong.

It took a while to figure out that the Dockero expects the Docker Unix socket to be at /var/run/docker.sock, but Colima has it at ~/.colima/default/docker.sock.

To make Dockero work, you have to set the DOCKER_HOST environment variable. For my Express-based application this meant adding to .env (no $HOME variable substitution here unfortunately):

DOCKER_HOST=unix:///Users/lptr/.colima/default/docker.sock

I also had some tests using Jest that involved executing Docker containers. Fixing those was a bit more complicated.

I first installed dotenv:

npm install dotenv --save-dev

Then in jest.config.ts I added:

import type { Config } from 'jest';

export default {
  // ...
  setupFiles: ['./jest.setup.ts'],
} as Config;

And in jest.setup.js:

import { config } from 'dotenv';

config({
  path: '.env.test',
  quiet: true,
});

This loads a .env.test file before tests executed by Jest, so I can also put the DOCKER_HOST in there.

I then later switched from Colima to Rancher Desktop. To make things work once again I had to change both .env files:

DOCKER_HOST=unix:///Users/lptr/.rd/docker.sock