Weave

A JIT configuration loader for Elixir

About

This library makes it possible to load configuration, especially secrets, from disk (Ala Docker Swarm / Kubernetes) on start-up.

Installation

def deps do
  [{:weave, "~> 2.1.2"}]
end

Configuration

config :weave,
  file_directories: ["/path/to/secrets"]  # Only needed when using the File loader
  environment_prefix: "MYAPP_",           # Only needed when using the Environment loader
  handler: Your.Handler,                  # Always needed :smile:
  loaders: [
    Weave.Loaders.File,
    Weave.Loaders.Environment
  ]

Manual Handler

Your handler is responsible for taking these environment variables, and/or files, and injecting their values into configuration.

handle_configuration/2 should return a tuple with the :app to set the key value pair on.

Weave will handle merging, so try not to worry about that 😄

Example

Lets assume:

• We are using the environment and file loaders
• We have the environment_prefix configured as MY_APP_
• We have an environment variable called MY_APP_NAME
• We have a file in configured secrets directory called db_password

Before being passed to your handler:

• All file-names and environment variables are lower-cased
• Environment variables have the prefix stripped

defmodule Your.Handler do
  def handle_configuration("name", value) do
    {:app, :name, value}
  end

  def handle_configuration("db_password", value) do
    {:app, :password, value}
  end

  # Sometimes you need to use the same value twice, so return a list.
  # NB: We *may* make returning lists the default in the future.
  def handle_configuration("kafka_host", host) do
    [
      {:kaffe, :consumer, [host: {String.to_atom(host): 9092}]},
      {:kaffe, :producer, [host: {String.to_atom(host): 9092}]}
    ]
  end
end

Auto Handler Example

Warning: We intially thought this would help you reduce all the boilerplate associated with writing handlers. We're now not sure this is really worth it. Use with caution.

In-order to cut down on the boilerplate, you can use the "handler-free" approach and ensure that the values of your environment variables, or contents of files, contain:

{:auto, :app, :name, value}

NB: For now, config :weave, handler: BLAH is still required, even if no handle_configuration/2 functions.

Loading Configuration

You'll need to add the following to your start function, before you prepare your supervisor:

Weave.configure()

If you really wish, you can omit :loaders during configuration and load from it manually:

Weave.Loaders.Environment.load_configuration()
Weave.Loaders.File.load_configuration()

Logging

Weave may log sensitive information at the debug level, stick to info in production.

Contributing

Running Tests with Docker

$ docker-compose run --rm elixir