When working with AWS EC2, it’s often handy to be able to reference certain information about an instance. The obvious solution is the AWS Metadata service, accessible with a simple cURL command. For example, to get the private IP address of an instance:

curl -s http://169.254.169.254/latest/meta-data/local-ipv4
172.1.2.3

Since I hate writing boilerplate code, and don’t need to make an HTTP request each time I want to know something about my environment, I put together a Docker image that fetches most of the available metadata and outputs environment variable settings. Also, I’ve been itching to write something in Go.

My primary use case is to create /etc/aws.env when a new CoreOS instance starts, but this should work on any system with systemd. To do this, aws-env.service should be installed and configured to run at startup. One way to do this is via cloud-config (EC2 User Data):

#cloud-config
coreos:
  units:
    - name: aws-env.service
      command: start
      enable: yes
      content: |
         [Unit]
         # Contents from 'aws-env.service' go here

Alternatively, you can use it with eval:

eval $(docker run --rm -t cmattoon/aws-env)

GitHub: https://github.com/cmattoon/aws-env

DockerHub: https://hub.docker.com/r/cmattoon/aws-env/