# Cai::Ecs::Entrypoint

This gem provides an easy and convenient method for Docker-based applications to retrieve configuration as environment variables at application startup.

## Installation

Add the following line to your application's `Dockerfile` as early as possible, preferrably following the `FROM` statement:

```dockerfile
FROM some/base

# If necessary, install Ruby runtime; omit if container already includes Ruby, such as a Rails app
RUN apt-get update && apt-get -y install ruby

# Install cai-ecs-entrypoint gem
RUN gem install cai-ecs-entrypoint -v 1.1.0
```

Installing the Ruby runtime and gem early in the Docker file allows Docker container layer caching and will improve build times.

## Usage

To use the gem, alter your container's `Dockerfile` to specify the `ENTRYPOINT`:

```dockerfile
ENTRYPOINT ["ssm-entrypoint"]
CMD ["your-executable", "arg1", "arg2", "...argN"]
```

The SSM Entrypoint requires two environment variables to be set when running the container:

* `AWS_REGION`: specifies the AWS region storing the SSM parameters used for this application
* `SSM_KEY_PATH`: path-notated prefix for all keys that the entrypoint should fetch, e.g. `/stage/myApp`

Both of these environment variables are provided _automatically_ for applications running on the Docker-based AWS Deployment Pipeline, such as used by CentralDispatch.

When using `docker-compose` locally, the entrypoint gem will _do nothing_, since proper AWS IAM credentials are required to fetch configuration. Use the `docker-compose.yml`, `docker-compose.override.yml`, or other mechanism, to provide environment variables locally.

In AWS, if the entrypoint script is unable to fetch configuration, the application will fail to start. This is _by design_ to prevent the application from starting in an unexpected or unpredictable state.

## Gem Development

After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).

## Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/cai-ecs-entrypoint.