Build a Galera cluster on a Docker Machine-provisioned Docker Swarm cluster

README.md

Build a Galera cluster on a Docker Swarm cluster made of Docker Machine-provisioned VMs

This repository contains scripts to create a Docker Swarm cluster of VirtualBox VMs and then start a Galera cluster of Docker containers running on the Swarm cluster.

The script create-cluster.sh will go through the following steps:

• Create the VMs, one to host the consul container which will act as the keystore for the Docker Swarm cluster, then some more as members of the cluster.
• Create an overlay network spanning all the Swarm cluster nodes so containers on one node can directly connect to others on other hosts.
• Create an initial Galera container which will act as an initial master for the Galera cluster.
• Create additional Galera containers and connect them to the growing Galera cluster.

Schema

.-----------------------------------------------.
|                                               |
| .-------------..-------------..-------------. |
| | Galera Node || Galera Node || Galera Node | |
| '-------------''-------------''-------------' |
| .-------------..-------------..-------------. |
| | Galera Node || Galera Node || Galera Node | |
| '-------------''-------------''-------------' |   Galera Cluster
| .-------------..-------------..-------------. |   on overlay network
| | Galera Node || Galera Node || Galera Node | |
| '-------------''-------------''-------------' |
|                                               |
'-----------------------------------------------'
.-----------------------------------------------.
|  ________   ________   ________   ________    |
| |==|=====| |==|=====| |==|=====| |==|=====|   |
| |  |     | |  |     | |  |     | |  |     |   |
| |  | VM  | |  | VM  | |  | VM  | |  | VM  |   |
| |  |     | |  |     | |  |     | |  |     |   |  Docker Swarm
| |  |     | |  |     | |  |     | |  |     |   |  Cluster     
| |  |====°| |  |====°| |  |====°| |  |====°|   |
| |__|_____| |__|_____| |__|_____| |__|_____|   |
|                                               |
'-----------------------------------------------'

Sources

• Docker docs: Get started with multi-host networking
• Galera docs: Getting started Galera with Docker, part 1

create-cluster.sh

#!/usr/bin/env bash

set -ex

which docker-machine || (echo docker-machine not found. ; exit 1)

create_host() {
	local HNAME=$1
	local KEYSTORE=$2
	log Create host "$HNAME" with keystore "$KEYSTORE".
	docker-machine create \
	-d virtualbox \
	--swarm --swarm-master \
	--swarm-discovery="consul://$(docker-machine ip  swarm-keystore):8500" \
	--engine-opt="cluster-store=consul://$(docker-machine ip $KEYSTORE):8500" \
	--engine-opt="cluster-advertise=eth1:2376" \
	$HNAME
}	

create_galera_node() {
	local NODENAME=$1
	local GALERAMASTER=$2
	local HOST=$3
	log Create Galera Node "$NODENAME" with Galera master "$GALERAMASTER" on host "$HOST".
	docker run -itd --name="$NODENAME" -h "$NODENAME" --net=galera-net --env="constraint:node==""$HOST" erkules/galera:basic --wsrep-cluster-name=local-test --wsrep-cluster-address=gcomm://"$GALERAMASTER"
}

log() {
	set +x
	echo -e "\033[34m[create-cluster] $* \033[0m"
	set -x
}

log Create VM for Docker Swarm Keystore

docker-machine create -d virtualbox swarm-keystore
eval "$(docker-machine env  swarm-keystore)"

log Run Consul container as Docker Swarm Keystore

docker $(docker-machine config swarm-keystore) run -d \
    -p "8500:8500" \
    -h "consul" \
    progrium/consul -server -bootstrap

log Create VMs

create_host swarm-node0 swarm-keystore
create_host swarm-node1 swarm-keystore
create_host swarm-node2 swarm-keystore

log Show VMs

docker-machine ls
eval $(docker-machine env --swarm swarm-node0)
docker info

log Create overlay network

docker network create --driver overlay galera-net
docker network ls

log Start initial Galera node

docker run -itd --name=galera-node0 -h galera-node0 --net=galera-net --env="constraint:node==swarm-node0" erkules/galera:basic --wsrep-cluster-name=local-test --wsrep-cluster-address=gcomm://

log Start additional Galera node containers

create_galera_node galera-node1 galera-node0 swarm-node0
create_galera_node galera-node2 galera-node0 swarm-node0
create_galera_node galera-node3 galera-node0 swarm-node1
create_galera_node galera-node4 galera-node0 swarm-node1
create_galera_node galera-node5 galera-node0 swarm-node1
create_galera_node galera-node6 galera-node0 swarm-node2
create_galera_node galera-node7 galera-node0 swarm-node2
create_galera_node galera-node8 galera-node0 swarm-node2

log Let the Galera cluster settle for 5s

sleep 5s

log Ask Galera cluster about its size

docker exec -ti galera-node0 mysql -e 'show status like "wsrep_cluster_size"'

destroy-cluster.sh

#!/usr/bin/bash

set -x

for i in swarm-keystore swarm-node{0..2} ; do
	docker-machine rm -f -y $i ;
done

How can you access to your galera cluster from the outside ? What would you configure to set a unique access point in your swarm cluster, to send some mysql requests to galera ? Is it possible without installing anything outside a docker context ?