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Hydrofoil (Crystal)

Opinionated, Alpine-based development container for Crystal

Features

  • Use Alpine (musl) as base to ease generation of static binaries
  • Use Crystal's official binary packages
  • Promote non-root container usage and proper file/directory ownership
  • Provide simple tools to certain dev related tasks (Eg. watch changes, process monitoring, etc)
  • Be continuously updated using GitHub Actions

This project does not aim to:

Overview

This project aims to be used only for development, replacing the local installation of tools for something consistent across OS and configurations.

It includes the minimum needed packages to have an usable Crystal compiler environment, leaving to you the option to add additional ones by using the offered image as base.

Additionally, it includes the following packages:

  • fixuid: tweaks container UID/GID to avoid ownership issues on mounted volumes
  • Overmind: Advanced Procfile-based process manager
  • watchexec: simple tool that watches a path and runs a command whenever it detects modifications

Requirements

The container images can be used directly with Docker, but is recommended to use in combination with docker-compose.

See below for usage examples.

Usage

To take full advantage of this container image, you need to adjust your docker-compose.yml primary service to use it:

services:
  app:
    image: ghcr.io/luislavena/hydrofoil-crystal:1.4
    command: overmind start -f Procfile.dev
    working_dir: /app

    # Set these env variables using `export FIXUID=$(id -u) FIXGID=$(id -g)`
    user: ${FIXUID:-1000}:${FIXGID:-1000}

    volumes:
      - .:/app:cached

Let's break down each element:

command: overmind start -f Procfile.dev

The container will execute Overmind process manager and start the processes indicated in the Procfile.dev file.

working_dir: /app

It adjusts the container working directory to be anything other than the default. This /app location will be used to mount our application code.

user: ${FIXUID:-1000}:${FIXGID:-1000}

This sets the user that will be used within the container to something other than root. A sudoers user has been setup and this instructions uses Docker's compose variable substitution to read your current user's UID/GID values and map correctly to the container user.

This technique helps eliminate root/non-root permission issues when working with mounted directories.

Is recommended you export these two variables (perhaps in your bash profile):

export FIXUID=$(id -u) FIXGID=$(id -g)

Finally, we have the mounted directories:

volumes:
  .:/app:cached

This mounts your current directory as /app within the container. Combined with working_dir makes it the working directory for all operations.

Other examples

You can find more advanced usage examples of this container image inside the examples directory.

Contribution Policy

This project is open to code contributions for bug fixes only. Features carry a long-term maintenance burden so they will not be accepted at this time. Please submit an issue if you have a feature you'd like to request or discuss.