Differences between revisions 7 and 43 (spanning 36 versions)

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.

192.168.1.59 redis01 (master)
192.168.1.60 redis02 (replica)
192.168.1.61 redis03 (replica)

Software

apt-get install redis-server redis-sentinel

Configuration

Redis Server

Change the contents of the redis configuration file in /etc/redis/redis.conf.

Add the IP-address for each of the servers. Each of the redis servers needs to listen on its own IP-address.

bind 192.168.1.59 127.0.0.1 ::1

Enable redis to listen on the network, instead of only listening on the loopback device.

protected-mode no

Now restart the redis master

service redis-server restart

And stop the replicas

service redis-server stop

On each of the replicas, set them up af a replica of the master

replicaof 192.168.1.59 6379

Start the replicas again

services redis-server start

You should now be able to see the replicas from the master redis-cli -h 192.168.1.59.

192.168.1.59:6379> info replication
# Replication
role:master
connected_slaves:2
slave0:ip=192.168.1.60,port=6379,state=online,offset=2615,lag=0
slave1:ip=192.168.1.61,port=6379,state=online,offset=2615,lag=1
master_replid:79a21f08669303e71990ea8819830f30c94384c6
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:2615
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1
repl_backlog_histlen:2615

Redis Sentinel

Change the contents of the redis configuration file in /etc/redis/sentinel.conf.

Add the IP-address for each of the servers. Each of the redis servers needs to listen on its own IP-address.

bind 192.168.1.59 127.0.0.1 ::1

Configure each of the hosts to monitor the master redis server, and at least 2 sentinels should agree to change the master

sentinel monitor redis01 192.168.1.59 6379 2

Set the time the redis master can be down

sentinel down-after-milliseconds redis01 5000

Finally set the timeout before the failover happens

sentinel failover-timeout redis01 30000

And finally

sentinel parallel-syncs redis01 1

-  ⇤ ← Revision 7 as of 2020-02-11 23:20:21 → 
  Size: 802
  Editor: Kristian Kallenberg
  Comment:
+   ← Revision 43 as of 2021-01-04 22:36:43 → ⇥
  Size: 3320
  Editor: Kristian Kallenberg
  Comment:
-Deletions are marked like this.
+Additions are marked like this.
 Line 1:
-INCOMPLETE DO NOT USE
-Line 7:
+Line 5:
- * 192.168.1.58 redis01
 * 192.168.1.59 redis02
 * 192.168.1.60 redis03
+ * 192.168.1.59 redis01 (master)
 * 192.168.1.60 redis02 (replica)
 * 192.168.1.61 redis03 (replica)
-Line 14:
+Line 12:
-apt-get install redis-server redis-sentinel redis-cli
+apt-get install redis-server redis-sentinel
-Line 19:
+Line 17:
-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.
+=== Redis Server ===
-Line 21:
+Line 19:
+Change the contents of the redis configuration file in `/etc/redis/redis.conf`.

Add the IP-address for each of the servers. Each of the redis servers needs to listen on its own IP-address.
-Line 22:
+Line 23:
-bind 127.0.0.1 192.168.1.58
+bind 192.168.1.59 127.0.0.1 ::1
-Line 25:
+Line 26:
-The same goes for `/etc/redis/sentinel.conf`
+Enable redis to listen on the network, instead of only listening on the loopback device.
-Line 27:
+Line 28:
-bind 127.0.0.1 192.168.1.58
+protected-mode no
}}}

Now restart the redis master
{{{
service redis-server restart
}}}

And stop the replicas
{{{
service redis-server stop
}}}

On each of the replicas, set them up af a replica of the master
{{{
replicaof 192.168.1.59 6379
}}}

Start the replicas again
{{{
services redis-server start
}}}

You should now be able to see the replicas from the master `redis-cli -h 192.168.1.59`.
{{{
192.168.1.59:6379> info replication
# Replication
role:master
connected_slaves:2
slave0:ip=192.168.1.60,port=6379,state=online,offset=2615,lag=0
slave1:ip=192.168.1.61,port=6379,state=online,offset=2615,lag=1
master_replid:79a21f08669303e71990ea8819830f30c94384c6
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:2615
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1
repl_backlog_histlen:2615
}}}

=== Redis Sentinel ===

Change the contents of the redis configuration file in `/etc/redis/sentinel.conf`.

Add the IP-address for each of the servers. Each of the redis servers needs to listen on its own IP-address.
{{{
bind 192.168.1.59 127.0.0.1 ::1
}}}

Configure each of the hosts to monitor the master redis server, and at least 2 sentinels should agree to change the master
{{{
sentinel monitor redis01 192.168.1.59 6379 2
}}}

Set the time the redis master can be down
{{{
sentinel down-after-milliseconds redis01 5000
}}}

Finally set the timeout before the failover happens
{{{
sentinel failover-timeout redis01 30000
}}}

And finally
{{{
sentinel parallel-syncs redis01 1
-Line 34:
+Line 102:
+ * 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/
 * https://www.tecmint.com/setup-redis-cluster-in-centos-8/
 * https://stackoverflow.com/questions/39568561/how-to-solve-redis-cluster-waiting-for-the-cluster-to-join-issue

Redis

Software

Configuration

Redis Server

Redis Sentinel

References