Differences between revisions 57 and 58
⇤ ← Revision 57 as of 2021-03-26 21:53:09 →
Size: 3990
Editor: Kristian Kallenberg
Comment:
← Revision 58 as of 2022-01-03 22:09:21 → ⇥
Size: 3706
Editor: Kristian Kallenberg
Comment:
Deletions are marked like this. Additions are marked like this.
Line 94: Line 94:
Set the time the redis master can be down
{{{
sentinel down-after-milliseconds mymaster 5000
}}}

Set the number of replicas who can change master at the same time. Setting this too high may cause none of the replicas to respond.
{{{
sentinel parallel-syncs mymaster 1
}}}

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.

  • 192.168.1.54 redis (virtual IP-address)
  • 192.168.1.55 redis01 (master)
  • 192.168.1.56 redis02 (replica)
  • 192.168.1.57 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 192.168.1.55 127.0.0.1

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

protected-mode no

For better dataintegrity enable this. 

appendonly yes

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. (This was earlier called slaveof) 

replicaof 192.168.1.55 6379

Start the replicas again 

services redis-server start

You should now be able to see the replicas from the master redis-cli -h 192.168.1.55. 

192.168.1.55:6379> info replication
# Replication
role:master
connected_slaves:2
slave0:ip=192.168.1.56,port=6379,state=online,offset=2615,lag=0
slave1:ip=192.168.1.57,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

Stop the sentinel 

service redis-sentinel stop

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 192.168.1.55 127.0.0.1

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

sentinel monitor mymaster 192.168.1.55 6379 2

Finally set the timeout before the failover happens 

sentinel failover-timeout mymaster 10000

Start the sentinel 

service redis-sentinel start

References

None: Redis (last edited 2022-01-03 22:09:21 by Kristian Kallenberg)