predixy/doc/Config-description-for-Redis-cluster.md

Configuration example

cluster.conf

ClusterServerPool {
    MasterReadPriority 60
    StaticSlaveReadPriority 50
    DynamicSlaveReadPriority 50
    RefreshInterval 300ms
    ServerTimeout 300ms                 #added in commit 86183a4
    ServerFailureLimit 2
    ServerRetryTimeout 500ms
    KeepAlive 120s                      #added in commit 86183a4
    Servers {
        + 192.168.2.107:2211
        + 192.168.2.108:2212
        + 192.168.2.109:2213
    }
}

Configuration parameters description

MasterReadPriority, StaticSlaveReadPriority and DynamicSlaveReadPriority - these parameters work in conjunction only in predixy and have nothing with Redis configuration directives like slave-priority. As predixy can work both with Redis Sentinel or Redis Cluster deployments, two options can be used: MasterReadPriority and StaticSlaveReadPriority, or MasterReadPriority and DynamicSlaveReadPriority.

If your Redis deployment implies nodes auto-discovery with Sentinel or other cluster nodes, the DynamicSlaveReadPriority option will be used; if you plan to add nodes in predixy config to Servers {...} manually, StaticSlaveReadPriority will be used.

In other words, predixy can discover automatically added Redis-related nodes polling existing Servers {...} and also route queries to them, eliminating the need of manually editing of cluster.conf and restarting the predixy.

These three parameters tell predixy in what way and proportion it should route queries to available nodes.

Some use cases you can see below:

Master/SlaveReadPriority	Master	Slave1	Slave2	Fail-over notes
60/50	all requests	0 requests	0 requests	Master dead, read requests deliver to slave until master(maybe new master) alive
60/0	all requests	0 requests	0 requests	Master dead, all requests fail
50/50	all write requests, 33.33%read requests	33.33% read requests	33.33% read requests	-
0/50	all write requests, 0 read requests	50% read requests	50% read requests	all slaves dead, all read requests fail
10/50	all write requests, 0 read requests	50% read requests	50% read requests	all slaves dead, read requests deliver to master

RefreshInterval - seconds, milliseconds or microseconds [s|ms|us], tells predixy how often it should poll nodes info and allocated hash slots in case of Cluster usage

ServerFailureLimit - amount of failed queries to node when predixy stop forwarding queries to this node

ServerTimeout - seconds, milliseconds or microseconds [s|ms|us], is timeout for nearly all commands except BRPOP, BLPOP, BRPOPLUSH, transactions and PUB/SUB. It's Redis server connection socket read/write timeout, to avoid wait for a Redis response too long. When timeout reached, Predixy will close connection between itself and Redis and throw an error. Available from the commit 86183a4.

KeepAlive - seconds, applied to redis connection(socket), it works for all commands that not covered with the ServerTimeout, i.e. applied also to commands with blocking nature like BRPOP, BLPOP, BRPOPLPUSH. hen timeout reached, Predixy will close connection between itself and Redis and throw an error. Available from the commit 86183a4.

ServerRetryTimeout - seconds, milliseconds or microseconds [s|ms|us], tells predixy how often it should try to check health of failed nodes and decide if they still failed or alive and can be used for queries processing

Servers - just line-by-line list of static Redis nodes in socket fashion, like + IP:PORT