NATS clustering made easy with CoreOS, etcd2 and Docker.
CoreOS uses etcd, a service running on each machine, to handle coordination between software running on the cluster. For a group of CoreOS machines to form a cluster, their etcd instances need to be connected.
A discovery service, https://discovery.etcd.io, is provided as a free service to help connect etcd instances together by storing a list of peer addresses, metadata and the initial size of the cluster under a unique address, known as the discovery URL. You can generate them very easily:
The discovery URL can be provided to each CoreOS machine via cloud-config, a minimal config tool that's designed to get a machine connected to the network and join the cluster.
This repository provides one cloud-config for you, but it will need some preparation in order to use a unique token for cluster discovery, as described above.
./setup 1
Replace 1 with the number of nodes you want your etcd cluster to have before bootstrapping. NATS won't run until the specified number of nodes is present in the cluster aka until etcd cluster bootstraps.
The output should be something like this:
$ ./setup 1
Retrieving discovery URL from discovery.etcd.io..
Discovery URL: [https://discovery.etcd.io/047a15e89b8d6c471df362c47f45525a]
Preparing cloud-config..
Done. Please use temp/nats.yaml cloud-config for provisioning your NATS cluster nodes.
You should now have a valid cloud-config with a unique discovery URL at ./temp/nats.yaml. Use it for provisioning your nodes.
According to the CoreOS documentation, this cloud-config will work only for the providers detailed below.
The $private_ipv4 and $public_ipv4 substitution variables referenced in other documents are only supported on Amazon EC2, Google Compute Engine, OpenStack, Rackspace, DigitalOcean, and Vagrant.