Docker Cookbook

10.5 DATA: Building a MySQL Galera Cluster on a Docker Network | 319

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The 
consul-server
machine is currently used by Docker Network, but this may
change. Currently we use this Consul server as a key-value store; the Docker engine
on each host uses it to store information about each host. As a reminder, check the
Vagrantfile and see the 
DOCKER_OPTS
specified at start-up; you will see that we also
define a default overlay network called 
multihost
.
Once the machines are up, 
ssh
to the first one and start the first node of your Galera
cluster by using the image 
erkules/galera:basic
. You can check the 
reference
 to see
what is in the Dockerfile used to build this image.
Let’s do it:
$ vagrant ssh mysql-1
$ docker run -d --name node1 -h node1 erkules/galera:basic \
--wsrep-cluster-name=local-test \
--wsrep-cluster-address=gcomm://
Get on host 
mysql-2
and start two additional Galera nodes. Note that you use the
node name 
node1
for the cluster address. This will work because Docker Network will
automatically properly define the 
/etc/hosts
file and it will contain the IP address of
node1
, 
node2
, and 
node3
. Since the three containers are in the same overlay, they will
be able to reach one another without any port mapping, container linking, or other
more complex network setup:
$ vagrant ssh mysql-2
$ docker run --detach=true --name node2 -h node2 erkules/galera:basic \
--wsrep-cluster-name=local-test \
--wsrep-cluster-address=gcomm://node1
$ docker run --detach=true --name node3 -h node3 erkules/galera:basic \
--wsrep-cluster-name=local-test \
--wsrep-cluster-address=gcomm://node1
Back on 
mysql-1
, you will see that after a short time, the two nodes started on
mysql-2
have automatically joined the cluster:
$ docker exec -ti node1 mysql -e 'show status like "wsrep_cluster_size"'
+--------------------+-------+
| Variable_name | Value |
+--------------------+-------+
| wsrep_cluster_size | 3 |
+--------------------+-------+
And indeed the 
/etc/hosts
file on the 
node1
container has the IP address of the other
two nodes:
$ docker exec -ti node1 cat /etc/hosts
...
172.21.0.6 node1.multihost
172.21.0.6 node1
172.21.0.8 node2
172.21.0.8 node2.multihost