Introduction

Currently Cloud Stack has only one active master DB setup. Going forward it should support multiple Master/Slave cluster setup to enable High Availability of the Database.

Scope

To Achieve Active/Active cluster set up (Multiple masters and slaves).

Options Available

1. MariaDB
2. Percona Xtra DB (uses Galera cluster)
3. MHA provided by SkySql
4. Mysql Active/Active setup with connector specific configuration to read from slaves in case of master goes down

Results

MariaDB

• It does not support any DB HA out of the box, we can use Galera with it but the same can be used with Mysql directly

  Percona Xtra DB

• It has the following limitations
  http://www.percona.com/doc/percona-xtradb-cluster/limitation.html

MHA

• It is very hard to install this and also need to write our own scripts to switch between master and slave either using VIP concept or some other way of LB

Mysql Active/Active Setup

We can use Mysql's 2-way replication (Master-Master replication setup) along with connector's configuration to read/write data from one of the slave if master goes down.

• It worked well with 2 nodes(master - master) set up for both fail over and fall back
• Need to verify the same for more than 2 nodes set up using chain replication with first 2 nodes as cyclic pointers for master/slaves and remaining are chain replication strategy starting from 2nd node.
• Also need to solve Communication link failure exception that is coming when master is going down.
• Admin guide steps to do the chain way of replication for multi node setup
• It works only when auto commit is true

Changes in Code Base (wrt mysql's active/active setup)

• Need to add extra properties related to connector parameters in db.properties
• Code changes are needed in com.cloud.utils.db.Transaction class to add the new properties to the url construction of cloud databases.