Etcd-aws-cluster NPM

etcd-aws-cluster

This container serves to assist in the creation of an etcd (2.x) cluster from an AWS auto scaling group. This is a fork from the upstream Monsanto repo, ported to Node.js. Much thanks to @tj-corrigan for doing the actual hard work of figuring out how to bootstrap etcd in AWS.

Docker Versions

1, 1.0 - (1/Dockerfile)
2, 2.0, latest - (master/Dockerfile)

Usage

This container should be run on the instance in the autoscaling group you wish to run the etcd node on. It will autodiscover the current status of the cluster, and write a set of etcd params to stdout.

$ docker run building5/etcd-aws-cluster

For cases where you cannot run a docker container (like starting up an etcd cluster you want to point you docker cluster at), you can also run from npm

$ npm install -g etcd-aws-cluster
$ etcd-aws-cluster

This output could be:

written to /etc/sysconfig/etcd-cluster for systemd startup. The output can then be loaded as an EnvironmentFile in an etcd2 drop-in to properly configure etcd2:
```
[Service]
EnvironmentFile=/etc/sysconfig/etcd-cluster
```
written to (or eval from) /etc/default/etcd for upstart startup
```
eval $(docker run building5/etcd-aws-cluster)
```

used with docker run --env-file for running in a docker container

$ docker run --env-file <(docker run building5/etcd-aws-cluster) etcd

The following params are written:

ETCD_NAME
- Node name; uses EC2 instance id
ETCD_LISTEN_CLIENT_URLS
- URL to listen on for client traffic; defaults to http://0.0.0.0:2379
ETCD_LISTEN_PEER_URLS
- URL to listen on for peer traffic; defaults to http://0.0.0.0:2380
ETCD_ADVERTISE_CLIENT_URLS
- URL to advertise for client traffic; defaults to http://:2379
ETCD_INITIAL_ADVERTISE_PEER_URLS
- URL to advertise for peer traffic; defaults to http://:2380
ETCD_INITIAL_CLUSTER_STATE
- new (spinning up new cluster) or existing (joining existing cluster)
ETCD_INITIAL_CLUSTER
- comma separated list of the other members of the cluster

Permissions

IAM permissions are needed to inspect the ASG and its members. The easiest way to do that is with an IAM instance profile. An example policy is given below, but you may want to narrow the Resource to the specific ASG the instance will belong to.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "Stmt1456626729000",
      "Effect": "Allow",
      "Action": [
        "ec2:Describe*",
        "autoscaling:Describe*"
      ],
      "Resource": ["*"]
    }
  ]
}

Workflow

get the instance id and ip from amazon
fetch the autoscaling group this machine belongs to
obtain the ip of every member of the auto scaling group
for each member of the autoscaling group detect if they are running etcd and if so who they see as members of the cluster
if no machines respond
- assume that this is a new cluster
- write a file using the ids/ips of the autoscaling group
else
- assume that we are joining an existing cluster
- check to see if any machines are listed as being part of the cluster but are not part of the autoscaling group
  - if so remove it from the etcd cluster
- add this machine to the current cluster
- write a file using the ids/ips obtained from query etcd for members of the cluster