Thinking transparent reconnects of applications is the grail of HA? It is! But Active/Active setups make them risky.
How the Continuent Proxy selects database cluster nodes for executing read operations.
Database Proxies provide a single entry point into MySQL for the calling client applications. Proxies are wonderful tools to handle various situations like a master role switch to another node for maintenance, or for transparency with read and write connections. However, when the time comes to perform the switch action, all of the calling clients have been funneled through the proxy, so identification of the calling host from the database itself becomes difficult.
When it comes to zero downtime, proxies are the first line components of a cluster. In order to achieve High Availability (HA) for MySQL, MariaDB and Percona Server, a commonly deployed setup consists of configuring load balancers (hardware or software) on top of those proxies.
You already know about the Tungsten Connector which is the "secret sauce" that routes your application database traffic to the appropriate MySQL data source of your cluster. Have you ever wondered how the Connector keeps track of the cluster configuration? How it always knows which host is the master (or masters in a Composite Multimaster topology), and which are slaves?
Achieving software upgrades without downtime is a challenge that few software products can handle, or even try to. Tungsten Clustering is one that can!
