Ec2Templater

Ec2Templater provides a means of EC2 service discovery by templating your server config.

It works by periodically querying AWS for the list of running EC2 instances, rendering a template, then running a notify command if it has changed. Using this setup you can provide, for example, a haproxy config that updates based on instances that are available filtered by tag.

For a full example, see the 'example' directory.

Note: AWS_REGION must be set by ENV var.

You must provide a way of grouping EC2's by configuring groups.

These groups are configured with a 'name' you can reference in your template, and a list of EC2 filters as described in the AWS documentation.

Finally, a notify command will be called when the rendered template has changed, enabling you to SIGHUP your server, or do a reload as required.

Provided config can include:

template:   template ERB source
target:     target file to write rendered template to
interval:   time in seconds between renders
notify_cmd: cmd to execute on change
vars:       (optional) hash of vars to make available to the renderer
groups:     hash of group names to ec2 filters, will be made available
            to the template as '@groups', with values changed to instances

The filters should match those defined for the describe-instances api call. http://docs.aws.amazon.com/cli/latest/reference/ec2/describe-instances.html

In your template, you can access groups as '@groups' which will be a copy of the above hash with ec2 instances for each group name in place of the filters.

The returned instances are Types::Instance from awssdk. See: http://docs.aws.amazon.com/sdkforruby/api/Aws/EC2/Types/Instance.html

Example:

---
template: '/etc/haproxy_templater/haproxy.erb.cfg'
target: '/etc/haproxy/haproxy.cfg'
interval: 60
notify_cmd: 'service haproxy reload'
vars:
  other_vars: value
groups:
  site_backends:
    tag:Environment: Production
    tag:Role: app
  kibana_backends:
   tag:Environment: Production
   tag:Role: log_index

Example @groups content:

{
  site_backends: [ec2_instance, ...],
  kibana_backends: [ec2_instance, ..]
}

Example invocation:

$ AWS_REGION=ap-southeast-2 bundle exec ec2_templater --config example/config.yml

Install the gem into your server either as a specific user, or system wide.

gem install 'ec2_templater'

Run the daemon via the executable "ec2_templater" and provide the configuration file with "-c":

ec2_templater -c /etc/ec2_templater/config.yml

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.

Note that the specs are built to run an EC2 instance, then terminate it, and the AWS API interactions have been recorded with VCR for fast playback. To regenerate, start with an empty AWS account, set VCR to record :all rather than :none, and rm -rf ./fixtures

Bug reports and pull requests are welcome on GitHub at https://github.com/reinteractive/ec2_templater. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

The gem is available as open source under the terms of the MIT License.