Differences between revisions 13 and 48 (spanning 35 versions)
⇤ ← Revision 13 as of 2020-02-13 20:03:47 →
Size: 1408
Editor: Kristian Kallenberg
Comment:
← Revision 48 as of 2021-01-08 21:15:35 → ⇥
Size: 3645
Editor: Kristian Kallenberg
Comment:
Deletions are marked like this. Additions are marked like this.
Line 1: Line 1:
INCOMPLETE DO NOT USE
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 * 192.168.1.58 redis01
 * 192.168.1.59 redis02
 * 192.168.1.60 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 21: Line 20:
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. Change the contents of the redis configuration file in `/etc/redis/redis.conf`.
Line 23: Line 22:
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).
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bind 127.0.0.1 192.168.1.58 bind 192.168.1.59 127.0.0.1
Line 27: Line 27:
Stop the redis server on all hosts. 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
Line 32: Line 42:
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`. On each of the replicas, set them up af a replica of the master
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slaveof 192.168.1.58 6379 replicaof 192.168.1.59 6379
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Start the redis servers again, but start it on redis01 first. Start the replicas again
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service redis-server start services redis-server start
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redis01 should now be the master.
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
}}}
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The same goes for `/etc/redis/sentinel.conf` 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.
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bind 127.0.0.1 192.168.1.58 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
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 * https://www.haproxy.com/blog/haproxy-advanced-redis-health-check/
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 * 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
 * https://www.willandskill.se/en/setup-a-highly-available-redis-cluster-with-sentinel-and-haproxy/

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

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

References

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