# DockerBuild

Library for building docker images.

## Installation

If [available in Hex](, the package can be installed
by adding `docker_build` to your list of dependencies in `mix.exs`:

def deps do
    {:docker_build, "~> 0.6.0", runtime: false, only: :dev}

## Basic Use

### Add configuration

Add the following entry in `mix.exs`: 

# mix.exs
  def project do
      docker_build: docker_build(),

  defp docker_build do
      plugins: [DockerBuild.Plugins.Webpack],
      app_name: :my_project,
      elixir_version: "1.12.3",
      docker_image: "docker.registry.url/my_project:production"

This example assumes that you are using webpack to compile assets.

### Build docker image

To build a release docker image:


The task generates a `.dockerignore` file in the root of the project so you will probably
want to add this to `.gitignore`.

A two-stage build is used so the final docker image will not contain source code.

### Run docker image
The build image can be run with
docker run docker.registry.url/my_project:production
However, this will probably fail if your project relies on environment variables at runtime.

## Advanced usage

### Additional configuration

The following additional config values are available:

  * `:extra_dockerignore` - a list of paths to add to the generated `.dockerignore` files. By
  default all files are excluded so it is likely you will want to use this to explicitly
  include files by prefixing them with `!`.
  * `:umbrella_apps` - list of apps in an umbrella project.  If not set then the project is
  assumed to be a non-umbrella project.
  * `:release_manager` - By default, the built-in release mechanism is used, however, if you wish to use distillery, set this to `:distillery`
  * `:plugin_paths` - list of path to source code for custom plugins in your project (see below).  Defaults to `["docker_build/lib"]`.

### Using assets

Add the `Assets` plugin:
plugins: [
  {DockerBuild.Plugins.Assets, assets_path: "/path/to/assets", nodejs_major_version: 14}
The default configuration is:
  `:assets_path` - `assets`
  `:nodejs_major_version` - 16

If you use the `Webpack` plugin and don't need to change any `Assets` default, you don't
need to explicitly include it as the `Webpack` plugin will include it automatically.

### Adding an ssh key to the build stage

You can add this in `deploy/ssh_keys`.  Add a public and private key, e.g.
`id_rsa` and ``.  They will be copied to the `/root/.ssh` folder in the build
stage docker image.

The typical use case for this is a deployment key to fetch some dependencies from a private
git repo.  In this case you may also need to use the `DockerBuild.Plugins.KnownHosts` plugin
to add the host of the source repo.

For example for a dependency that is in a private Github repo:

1. Generate a new key pair:
mkdir -p deploy/ssh_keys
ssh-keygen -f deploy/ssh_keys/id_rsa -N "" -C my_project-docker-build

2. Go to the deployment keys section for your dependency
in Github's UI (*Settings -> Deploy keys*) and add a new key with the
contents of ``.

3. Add `` to the `KnownHosts` plugin.
plugins: [
  {DockerBuild.Plugins.KnownHosts, hosts: [""]}

N.B.  You can only add one ssh key using this method.  Github currently does not permit
re-use of deployment keys in different repos, so if you have multiple private repos that are
used by your project then this will not work.  Even if multiple ssh keys could be added, then
when attempting to clone the repo, git would not know which one to use and does not retry if
the first key fails.

An alternative mechanism for cloning private repos is to use https authentication.  This can
be done by creating a personal access token in github and then specifying the git URL with the
authentication details. e.g. `git clone`

Alternatively provide a curl `.netrc` file (see below)

### Adding a curl .netrc file

You can add this in `deploy/.netrc`.  This can be used to clone dependencies from a private git
repo using a personal access token.  This will be used by `curl` when cloning the repos.

Example `deploy/.netrc` file contents:
login <github username>
password <gitub personal access token>

## Plugin System

A plugin system is available to extend the dockerfile that is generated via various callbacks.

In the config a list of plugins can be given.  Each item can either be the module name (if no
configuration is required), or a tuple of the plugin and a keyword list of config values to provide
a list of config values to the plugin:

# config/dev.exs
config :docker_build, DockerBuild.Build,
  plugins: [PluginModule1, {PluginModule2, foo1: :bar1, foo2: :bar2}`, PluginModule3],

There are several plugins already included in the project.

### Custom plugins

You can also create your own custom plugin in your project.  You should put the source code for this in
`docker_build/lib` so it is outside the normal compile paths for Elixir and thefore not included in the build.  You can change this 
using the `:plugin_paths` config key.

## Troubleshooting

### Host key verification failed error

If you see this when fetching dependencies, ensure that you have the source repo
added to `DockerBuild.Plugins.KnownHosts` plugin.

### The webserver does not start

Ensure that you have set `server: true` in you endpoint:

# config/prod.exs
config :my_app, MyApp.Endpoint,
  server: true

## Design Decisions

### Selection of environment

The environment to build under (i.e. what `MIX_ENV` is set to in Docker) is set from the command line.  This has the following advantage over taking the current value of `MIX_ENV` when invoking the task:

1. When building a `prod` release the project and dependencies do not need to be compiled locally with `MIX_ENV=prod` just to run the mix task.


### Verify config keys are valid
* Raise an error if unknown config or plugin config keys are supplied

### Use .tool-versions
* Provide an option to get the version from .tool-versions file

* Allow a config for `:docker_host` so you don't need to pass with env var

### Check mandatory config params

Currently a protocol error is shown if the config is missing.

### Extract SSH Keys copy to plugin

### Add Migration plugin
  * This would need to add a `` to the image which would take a command which would
  either be `start` or `migrate` to run the migrations.
  * This could also generate the code needed to run migrations either via a library function
  or a macro.  This could be tricky as currently the library only runs in `MIX_ENV=dev`
  * Alternatively add support for tasks, one of which could by `migrate`