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| Deletions are marked like this. | Additions are marked like this. |
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| DISCLAIMER: This is running in Buster |
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| * 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) |
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| apt-get install redis-server | apt-get install redis-server redis-sentinel |
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| Add the IP-address for each of the servers. Each of the redis servers needs to listen on its own IP-address. Due to a bug in redis, the added IP-address will have to be in the beginning of the line, right next to `bind`. If the IP-address is added in the end of the line, then the cluster will not initialize itself, and a `Waiting for the cluster to join...` message will continuously write dots. | 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 192.168.1.58 127.0.0.1 ::1 | bind 192.168.1.59 127.0.0.1 |
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| 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 changes in a file on disk. | For better dataintegrity enable this. |
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| Activate redis cluster features {{{ cluster-enabled yes cluster-config-file nodes-6379.conf cluster-node-timeout 15000 }}} Restart redis on all hosts. |
Now restart the redis master |
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| Next we will need to configure the servers to run as a cluster | And stop the replicas |
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| redis-cli --cluster create 192.168.1.59:6379 192.168.1.60:6379 192.168.1.61:6379 | service redis-server stop |
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| You should get output similar to this | On each of the replicas, set them up af a replica of the master |
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| >>> Performing hash slots allocation on 3 nodes... Master[0] -> Slots 0 - 5460 Master[1] -> Slots 5461 - 10922 Master[2] -> Slots 10923 - 16383 M: 78252519c58c5e7651554b3c82ba5800e4c11c41 192.168.1.59:6379 slots:[0-5460] (5461 slots) master M: b26d5a1ebe4891c68acf1d6b7cea5cc19057849f 192.168.1.60:6379 slots:[5461-10922] (5462 slots) master M: 0db96b401cca249b61660ed4d2945d658dcdc6e1 192.168.1.61:6379 slots:[10923-16383] (5461 slots) master Can I set the above configuration? (type 'yes' to accept): yes >>> Nodes configuration updated >>> Assign a different config epoch to each node >>> Sending CLUSTER MEET messages to join the cluster Waiting for the cluster to join >>> Performing Cluster Check (using node 192.168.1.59:6379) M: 78252519c58c5e7651554b3c82ba5800e4c11c41 192.168.1.59:6379 slots:[0-5460] (5461 slots) master M: 0db96b401cca249b61660ed4d2945d658dcdc6e1 192.168.1.61:6379 slots:[10923-16383] (5461 slots) master M: b26d5a1ebe4891c68acf1d6b7cea5cc19057849f 192.168.1.60:6379 slots:[5461-10922] (5462 slots) master [OK] All nodes agree about slots configuration. >>> Check for open slots... >>> Check slots coverage... [OK] All 16384 slots covered. |
slaveof 192.168.1.59 6379 |
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| 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 }}} 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 192.168.1.59 6379 2 }}} Set the time the redis master can be down {{{ sentinel down-after-milliseconds mymaster 5000 }}} Set this, although I do not know what that means. {{{ sentinel parallel-syncs mymaster 1 }}} Finally set the timeout before the failover happens {{{ sentinel failover-timeout mymaster 10000 }}} |
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| * 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
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
slaveof 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
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 192.168.1.59 6379 2
Set the time the redis master can be down
sentinel down-after-milliseconds mymaster 5000
Set this, although I do not know what that means.
sentinel parallel-syncs mymaster 1
Finally set the timeout before the failover happens
sentinel failover-timeout mymaster 10000
References
https://www.haproxy.com/blog/haproxy-advanced-redis-health-check/
https://blog.usejournal.com/first-step-to-redis-cluster-7712e1c31847
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.willandskill.se/en/setup-a-highly-available-redis-cluster-with-sentinel-and-haproxy/