Redis

Redis is an in memory data structure storage. It will be used to share PHP-sessions between the apache servers. To guarantee a robust deployment three redis servers will be configured.

192.168.1.58 redis01
192.168.1.59 redis02
192.168.1.60 redis03

Software

apt-get install redis-server redis-sentinel

Configuration

Redis Server

Make sure the apache servers can reach redis. Change bind 127.0.0.1 in /etc/redis/redis.conf. Each of the redis servers needs to listen on its own IP-address.

bind 127.0.0.1 192.168.1.58

Enable Redis to listen on the network

protected-mode no

Stop the redis server on all hosts.

service redis-server stop

To enable replication we need to consider one of the redis servers the master. Here it will be redis01. On the two other hosts add the following to /etc/redis/redis.conf.

slaveof 192.168.1.58 6379

Start the redis servers again, but start it on redis01 first.

service redis-server start

redis01 should now be the master.

Redis Sentinel

The same goes for /etc/redis/sentinel.conf

bind 127.0.0.1 192.168.1.58

-  ⇤ ← Revision 9 as of 2020-02-11 23:58:15 → 
  Size: 1269
  Editor: Kristian Kallenberg
  Comment:
+   ← Revision 19 as of 2021-01-02 00:19:42 → ⇥
  Size: 1991
  Editor: Kristian Kallenberg
  Comment:
-Deletions are marked like this.
+Additions are marked like this.
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+Enable Redis to listen on the network

{{{
protected-mode no
}}}
-Line 32:
+Line 39:
-To enable replication we need to consider one of the redis servers the master. Here it will be redis03. On the two other hosts add the following to `/etc/redis/redis.conf`.
+To enable replication we need to consider one of the redis servers the master. Here it will be redis01. On the two other hosts add the following to `/etc/redis/redis.conf`.
-Line 34:
+Line 41:
-slaveof 192.168.1.60 6379
+slaveof 192.168.1.58 6379
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+Line 44:
-Start the redis servers again, but start it on redis03 first.
+Start the redis servers again, but start it on redis01 first.
-Line 41:
+Line 48:
-redis03 should now be the master.
+redis01 should now be the master.
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+Line 61:
+ * https://www.haproxy.com/blog/haproxy-advanced-redis-health-check/
 * https://medium.com/@amila922/redis-sentinel-high-availability-everything-you-need-to-know-from-dev-to-prod-complete-guide-deb198e70ea6
 * https://blog.usejournal.com/first-step-to-redis-cluster-7712e1c31847
 * https://www.linode.com/docs/applications/big-data/how-to-install-and-configure-a-redis-cluster-on-ubuntu-1604/
 * https://www.willandskill.se/en/setup-a-highly-available-redis-cluster-with-sentinel-and-haproxy/
 * https://www.tecmint.com/setup-redis-replication-in-centos-8/
 * https://www.tecmint.com/setup-redis-high-availability-with-sentinel-in-centos-8/

Redis

Software

Configuration

Redis Server

Redis Sentinel

References