We use etcd for master election of orchestrator nodes to perform a scheduled task link poll or performance discovery.


This is an example tutorial to create a three machine etcd cluster with the following details:


<code>
Name	Address	Hostname
infra0	10.0.1.10	infra0.err
infra1	10.0.1.11	infra1.err
infra2	10.0.1.12	infra2.err
</code>

As we know the cluster members, their addresses and the size of the cluster before starting, we can use an offline bootstrap configuration by setting the initial-cluster flag. Each machine will get either the following environment variables or command line:

<code>
ETCD_INITIAL_CLUSTER="infra0=http://10.0.1.10:2380,infra1=http://10.0.1.11:2380,infra2=http://10.0.1.12:2380"
ETCD_INITIAL_CLUSTER_STATE=new
--initial-cluster infra0=http://10.0.1.10:2380,infra1=http://10.0.1.11:2380,infra2=http://10.0.1.12:2380 \
--initial-cluster-state new
</code>

Note that the URLs specified in initial-cluster are the advertised peer URLs, i.e. they should match the value of initial-advertise-peer-urls on the respective nodes.

If spinning up multiple clusters (or creating and destroying a single cluster) with same configuration for testing purpose, it is highly recommended that each cluster is given a unique initial-cluster-token. By doing this, etcd can generate unique cluster IDs and member IDs for the clusters even if they otherwise have the exact same configuration. This can protect etcd from cross-cluster-interaction, which might corrupt the clusters.

etcd listens on listen-client-urls to accept client traffic. etcd member advertises the URLs specified in advertise-client-urls to other members, proxies, clients. Please make sure the advertise-client-urls are reachable from intended clients. A common mistake is setting advertise-client-urls to localhost or leave it as default if the remote clients should reach etcd.

On each machine, start etcd with these flags:

<code>
$ etcd --name infra0 --initial-advertise-peer-urls http://10.0.1.10:2380 \
  --listen-peer-urls http://10.0.1.10:2380 \
  --listen-client-urls http://10.0.1.10:2379,http://127.0.0.1:2379 \
  --advertise-client-urls http://10.0.1.10:2379 \
  --initial-cluster-token etcd-cluster-1 \
  --initial-cluster infra0=http://10.0.1.10:2380,infra1=http://10.0.1.11:2380,infra2=http://10.0.1.12:2380 \
  --initial-cluster-state new
</code>

<code>
$ etcd --name infra1 --initial-advertise-peer-urls http://10.0.1.11:2380 \
  --listen-peer-urls http://10.0.1.11:2380 \
  --listen-client-urls http://10.0.1.11:2379,http://127.0.0.1:2379 \
  --advertise-client-urls http://10.0.1.11:2379 \
  --initial-cluster-token etcd-cluster-1 \
  --initial-cluster infra0=http://10.0.1.10:2380,infra1=http://10.0.1.11:2380,infra2=http://10.0.1.12:2380 \
  --initial-cluster-state new
</code>

<code>
$ etcd --name infra2 --initial-advertise-peer-urls http://10.0.1.12:2380 \
  --listen-peer-urls http://10.0.1.12:2380 \
  --listen-client-urls http://10.0.1.12:2379,http://127.0.0.1:2379 \
  --advertise-client-urls http://10.0.1.12:2379 \
  --initial-cluster-token etcd-cluster-1 \
  --initial-cluster infra0=http://10.0.1.10:2380,infra1=http://10.0.1.11:2380,infra2=http://10.0.1.12:2380 \
  --initial-cluster-state new
</code>

The command line parameters starting with --initial-cluster will be ignored on subsequent runs of etcd. Feel free to remove the environment variables or command line flags after the initial bootstrap process. If the configuration needs changes later (for example, adding or removing members to/from the cluster)