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Redis multiple server configuration questions

How does Redis communicate between master and slave?

The Redis cache runs as a Windows Service. In a multiple server configuration, Redis supports master-slave asynchronous replication and optionally provide high availability with Redis Sentinel.

Are two application servers required?

The default configuration for Changepoint is to install a Redis cache service on each Changepoint web server. Typically, the Redis service is not installed externally on a separate server. 

If you are setting up multiple Changepoint websites on a single web server (for example, for test and development environments), then each website requires its own Redis service instance to be installed.  Be sure that the Redis service instances have unique service names and port numbers, and that the websites are configured to the corresponding Redis service instance.

If you have Changepoint load-balanced across multiple web servers (for production), you must do one of the following:

  • Dedicate one of the installed Redis instances as the cache service for the all web servers. 
  • “Pool” the installed Redis instances to create a master-slave configuration to  provide high availability. 

How does a load balancer work with a master-slave configuration?

A load balancer does not apply to a Redis master-slave configuration. With Redis, there can only be one master instance, and all application interactions are done through the predefined master instance. 

There is no direct interaction with slave instances. The purpose of the slave instances is to retain copies of the master cache for redundancy and performance. The slaves only come into use during a failover, when a slave instance is promoted as the master and takes over the interaction with applications. The failover can be performed manually by an administrator who updates the configuration directly, or automatically through the Redis Sentinel service that runs alongside each Redis cache service.

For more information on how to set this up, please check the installation guide for your Changepoint version.