MySQL Clustering

The LifeKeeper® for Linux MySQL Recovery Kit provides an easy way to add LifeKeeper fault-resilient protection for MySQL resources and databases. This enables a failure on the primary database server to be recovered on a designated backup server without significant lost time or human intervention.

LifeKeeper is able to monitor all resources used by an application (IP, Disk, Volume) as well as checking that the application itself is running (for example it could execute a known data query). This proactive approach allows LifeKeeper to migrate an application in the event of a failure (for instance a network failure, local network card failure or even disk failure) to a different host.

In a shared storage environment

LifeKeeper can manage shared storage, and determine when to failover in the event of a localised failure on the local machine. The image below illustrates LifeKeeper in a shared storage configuration.

Data Replication - eliminating the need for shared storage

If shared storage is not available, LifeKeeper's data replication software can be used to mirror data to a remote server, and seamlessly handle the switchover in the event of a failure.

When data is written to disk, LifeKeeper data replication will mirror that data to a remote server. This ensures that the data is up to date in the event of a server or disk failure. The MySQL recovery kit enables switchover of MySQL applications to a backup server.

The data replication can occur on either a LAN or a WAN, and either synchronous or asynchronous approaches are available. (Under Linux asynchronous is not currently available due to a kernel restriction). Because the data replication software only transmits changes in data, and reads at the raw block level, it is efficient, versitile, relatively fast and is not dependant upon the file system type being used by the operating system.

The image below illustrates the replication of data from one active node, to another backup node using the Extended Replication software. Because the backup server will have an up to date copy of the data held on the active server, failover can occur at any time.

Data replication over a Wide Area Network

The below image illustrates the data replication taking place over a Wide Area Network. As mentioned above, due to the efficiency of the data replication software, it is feasible for replication to take place to a remote site, allowing for optimal disaster recovery and data protection.

LifeKeeper can run in an Active/Active or Active/Backup configuration

The diagrams so far have all shown MySQL running with LifeKeeper protection, in an Active/Backup configuration - i.e. one machine is always idle in case of emergency, this is an optimal configuration if performance is an issue. In some environments this redundancy of hardware may not be desirable, and a slight degradation of service may be acceptable over a short period of time (until the fault can be fixed with the primary server) and LifeKeeper can run in an Active/Active configuration as shown by the below diagrams.

The above diagrams show how LifeKeeper runs in an Active/Active configuration, where on failure on one node, the other node takes over and runs both services locally. An Active/Active configuration may use either shared storage, or the data replication discussed above. The Active/Active configuration allows for optimal resource usage combined with high availabilty; although in the event of a failover it is possible for performance to suffer if a server becomes heavily loaded.

LifeKeeper in an N+1 Configuration

Alternatively, if many servers are to be used, it is feasible to have an N+1 configuration where one machine acts as a backup to numerous active servers. In the event of more than one failovers occurring, the applications can fail over to any other active machines, in an order determined by the administrator during installation / initial configuration.

Original Source: www.openminds.co.uk