Differences between revisions 20 and 47 (spanning 27 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.

192.168.1.58 redis (virtual IP-address)
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. Make sure to add its IP-address in the beginning on the line. (running as a cluster currently requires this due to a bug, so we will do this although we are not setting up a cluster).

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 20 as of 2021-01-02 01:25:07 → 
  Size: 1996
  Editor: Kristian Kallenberg
  Comment:
+   ← Revision 47 as of 2021-01-08 21:14:15 → ⇥
  Size: 3649
  Editor: Kristian Kallenberg
  Comment:
-Deletions are marked like this.
+Additions are marked like this.
 Line 1:
-DISCLAIMER
THIS ONLY WORKS IN BUSTER
INCOMPLETE DO NOT USE
-Line 9:
+Line 5:
- * 192.168.1.59 redis01
 * 192.168.1.60 redis02
 * 192.168.1.61 redis03
+ * 192.168.1.58 redis (virtual IP-address)
 * 192.168.1.59 redis01 (master)
 * 192.168.1.60 redis02 (replica)
 * 192.168.1.61 redis03 (replica)
-Line 16:
+Line 13:
-apt-get install redis-server
+apt-get install redis-server redis-sentinel
-Line 25:
+Line 22:
-Add the IP-address for each of the servers. Each of the redis servers needs to listen on its own IP-address.
+Add the IP-address for each of the servers. Each of the redis servers needs to listen on its own IP-address. Make sure to add its IP-address in the beginning on the line. (running as a cluster currently requires this due to a bug, so we will do this although we are not setting up a cluster).
-Line 27:
+Line 24:
-bind 127.0.0.1 192.168.1.58
+bind 192.168.1.59 127.0.0.1 ::1
-Line 29:
+Line 26:
-Line 36:
+Line 32:
-Redis stores its data in memory only, hence its speed. To make sure redis does not loose its state, in case of a hardware failure, this will enable it to store the state as it changed in a file on disk.
+Now restart the redis master
-Line 38:
+Line 34:
-appendonly yes
+service redis-server restart
-Line 41:
+Line 37:
-Activate redis cluster features
+And stop the replicas
-Line 43:
+Line 39:
-cluster-enabled yes
cluster-config-file nodes-6379.conf
cluster-node-timeout 15000
+service redis-server stop
-Line 48:
+Line 42:
-Restart the redis server on all hosts.
+On each of the replicas, set them up af a replica of the master
-Line 50:
+Line 44:
-service redis-server restart
+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 64:
+Line 110:
+ * 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
 * https://www.willandskill.se/en/setup-a-highly-available-redis-cluster-with-sentinel-and-haproxy/

Redis

Software

Configuration

Redis Server

Redis Sentinel

References