Client for redis Highly Available set for Yii2 ¶

1. Workflow of connection process
2. Adviced configuration
3. Usage

This Yii2 component is based on core yii2-redis component https://github.com/yiisoft/yii2-redis but gives ability to work with master-slave redis clusters with sentiels.
It's rather simple - gets master server address from given sentinels and connects to it, then operates just like \yii\redis\Connection.
It works with sentinels only, does not connect to redis hosts without sentinels.

Workflow of connection process ¶

Loop over given sentinels and search for an alive one that will give a master host address.
If a sentinel does not respond or it's respond is empty, then we'll try to check the next one.
If no successfull reply was received, then connection will fail.
After we've found a redis master, we'll connect to it.
If connection to the master server fails, we won't try anything else, we'll fail.
If we sucessfully connect to the master server, we'll then check with `role` command if it really is master (http://redis.io/topics/sentinel-clients).
If it's not - we'll fail, if it really is - we're sucessfully connected.

Adviced configuration ¶

Redis HA cluster must be done with minimum 2 redis servers and 3 sentinels.
I suppose that in termes of performance, considering this implementation it's better to have a sentinel server for each app locally, to avoid unnecessary overheads.
That would not be important if we cached previously givem master server, but we dont. We ask sentinel each time before connecting to redis.
That's how I see a simple architecture:

    -------                    -------
   |       |                  |       |
   | Redis |                  | Redis |
   |       |                  |       |
    ------- \                 /-------
       |     \               /   |
       |      \             /    |
       |       \-----------/     |
       |       |\         /|     |
       |       |  Sentinel |     |
       |       |   .    .  |     |
       |        --.------.-      |
       |         .        .      |
       |        .          .     |
  -----|-------.---        -.----|----------     
 |     |      .    |      |  .   |          |    
 |    Sentinel. . .| . . .|. . Sentinel     |    
 |         |       |      |         |       |    
 |  (localhost)    |      |  (localhost)    |    
 |         |       |      |         |       |    
 |         |       |      |         |       |    
 |        APP      |      |        APP      |    
 |                 |      |                 |    
  -----------------        -----------------     
   

Usage ¶

Basic example: ~~~

			'session' => [
					'class' => '\yii\redis\Session',
					'redis' => [
						'class' => '\pyurin\yii\redisHa\Connection',
						'sentinels' => [
								'localhost'
						]
					]
			],

Sentinel servers are queried in the same order as exist in array.<br />

Installation
=============================================
Available with composer:

"require" : {

"pyurin/yii2-redis-ha":"*"

}, ~~~ Github: https://github.com/pyurin/yii2-redis-ha</a>