load balancing MySQL – any database, really – is not a trivial task. Generally speaking one does not simply round robin your way through a cluster of MySQL databases as a means to achieve scalability. It is databases, in fact, that have driven a wide variety of scalability patterns such as sharding and partitioning to achieve the ultimate goal of high-performance and scalability simultaneously.
Unfortunately, most folks don’t architect their applications with scalability in mind. A single database is all that’s necessary at first, and because of the way in which the application interacts with the database, it doesn’t make sense to code in support for multiple database instances, such as is often implemented with a MySQL master-slave cluster. That’s because the application has to actually open a connection to the database in question. If you’re only starting with one database, you really can’t code in a connection to a separate instance.
Eventually that application’s usage grows and the demands upon the database require a more scalable approach. Enter the MySQL master/slave relationship. A typical configuration is to maintain the master as the “write” database, i.e. all updates and/or inserts must use the master, while the slave instance is used as a “read only” instance.
Obviously this means the application code must be changed to support this kind of functional sharding. Unless you leverage network server virtualization from a load balancing service capable of acting as a full-proxy at layer 7 (application) like BIG-IP.
This solution leverages iRules to implement database load balancing. While this specific example is designed to perform the common functional sharding pattern of read-write separation for a master-slave MySQL cluster, the flexibility of iRules is such that other architectural solutions can easily be designed using the same basic functions. Location based sharding is another popular means of scaling databases, and using the GeoLocation capabilities of BIG-IP along with iRules to inspect and route database requests, it should be a fairly trivial architectural task to implement.
The ability to further extend sharding or other distribution methodologies for scaling databases without modifying the application itself is a huge bonus for both developers and operations. By decoupling the application from the database, it provides a more flexibility set of scalability domains in which technology targeted scalability strategies can be leveraged independent of the other layers. This is an important facet of agile infrastructure architecture and should not be underestimated as a benefit of network server virtualization.