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Dan Everton


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One of the things I’ve been experimenting with is Terraform from Hashicorp. It provides a simple configuration language for describing infrastructure that fills in the gap left by configuration tools like Puppet, Salt, and Ansible. Those tools can only describe what happens after a machine is created, not how to create that machine.

I thought I’d try and create the beginnings of a typical production test environment with split public and private networks. None of these networks are visible outside of the VPC. Instead a bastion host is used that also doubles as the NAT gateway.

To simplify service discovery I also deployed Consul to act as the DNS provider for hosts within the VPC. I started this work before Route 53 supported split-horizon DNS so I’m not sure if you still need to use Consul for this.

You can see the result of the experiment on my terraform-aws-consul respository on Github. It should work out of the box with Terraform 0.3.5 which was the latest at time of writing. The readme in that repository should cover the details of how to get going. Only t2.micro instances are used so it should cost you nothing (or very little) to deploy.

There’s a few things I had to figure out along the way that weren’t particularly obvious. The trickiest was getting the cloud-init files for userdata in to the right MIME multi-part format and keeping them in-sync with the component files. I hadn’t written a Makefile in years but it neatly solved the problem of running write-mime-multipart when needed.

Another trick was realising that you can tag instances in EC2 with Name and that will control the instance name on the EC2 dashboard. This was particularly handy for the Consul member nodes to make them easy to identify as consul1, consul2, etc.

The final trick was getting the DHCP settings sorted for Amazon Linux so that the instances would still get IPs from DNS, but have a resolv.conf modified to use a local Consul instance for DNS. This turned out actually be supported by modifying the dhclient configuration in cloud-init.

While this experiment doesn’t actually do all that much in the end, it seems like a good starting point. From here I’d like to actually deploy some applications and have them register with Consul. In a different experiment I’ve used Mesos and Marathon for this, but that’s another post.