We have an application with Redis Sentinel(3 sentinel 1 master 1 slave). We don't need replication at all. How can I turn off replication?
The command SLAVEOF NO ONE, when sent to a slave, will turn off the replication. The slave will become a master.
If you disable replication, you probably don't need Redis Sentinel either.
Related
Question Background:
I deploy a redis cluster in k8s cluster and use Redis-Sentinel to implement ha for redis cluster. My redis cluster structure likes below:
One master
One slave
three sentinel （serve a specific redis cluster)
When i login the container of the one of sentinels, i execute a command:
sentinel sentinels mymaster
Luckly, i get a desirable output. These are two sentinel's infos. After a period of time, i execute "sentinels mymaster" command again, i found that there is a additional sentinel and don't find this instance through IP address or runId。
I know that sentinel discover other sentinels and master and slave through sub the channel of sentinel:hello in redis master.
Question:
how to check the message published from redis sentinel to redis master? I have opened log for master and set the log level to debug.
You can see the Sentinel's activity (when it discovers a sentinel, a replica, failsover to a new master, etc.) in the sentinel log file, not the master. If a sentinel is running on a host, it will be in the same directory the master or replica log file is. For me on CentOS it's /var/log/redis/sentinel.log.
Suppose I have the following Redis replication setup:
3 machines
Each machine has a Redis server and a Redis sentinel.
One of the servers is set as master, the other two are its slaves.
What would be the correct sequence and commands to gracefully shutdown this setup, all while keeping the existing master as master and existing slaves as slaves (meaning, no failover or reconfig should take place)
Thanks.
Shutdown sequence
You should shutdown sentinels first, to avoid alarms/notifications and failover. Then you can shutdown slaves and master.
Shutdown command
You can gracefully shutdown Redis instances (sentinel, slave and master) with the shutdown command.
For Redis version older than 3.0 (not very sure), there's no shutdown command for Redis sentinel. But you can just use killall or kill -9 process_id to kill it without any side effect.
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UPDATE
In my original answer, I suggested shutdown slaves and master first, to avoid alarms from sentinel. In fact, there's another way to avoid alarms. You can simply remove the master from sentinel before shutdown the master: SENTINEL REMOVE <name>. After removing the master, you don't need to care the shutdown order any more.
How about the startup order?
If you use SENTINEL MONITOR <name> <ip> <port> <quorum> command to dynamically add a master to monitor, you can startup sentinel, and add masters dynamically. Instead, if you add the master with sentinel's configuration file, you can startup Redis first, to avoid alarms from sentinel.
I have a redis sentinel configuration with one master, two slaves and 3 sentinels running. I noticed that at some point the sentinels may switch the master electing one of the slaves as master. This is causing problems to an application which is connecting to the master node as a standalone client(I'm working on changing the code to use sentinels). I wanted to know if it is possible to switch the master by connecting to the sentinel client i.e. through 'redis-cli'
Can somebody let me know if there is a command that I can use to switch the master IP?
The client applications should use a client library that supports sentinel in the case where a redis master goes down and the sentinels select a new master. Not sure how beneficial it is to have sentinel setup if your client applications are not taking advantage of it. A client application that supports sentinel will query sentinel for the master ip and should be somewhat tolerant to faults occurring with the master connection. You can trigger a manual failover like the other answer states:
redis-cli -h {sentinel-ip} -p {26379 or sentinel port} sentinel failover {mastername}
But you will not be able to pick which node it fails over to. You can control a configuration value slave_priority in the redis.conf file so that it prefers a node over the rest. A description of the slave priority can be found here: https://redis.io/topics/sentinel
You can manually trigger a failover by running:
redis-cli -a {password} -p {sentinel_port} SENTINEL failover {cluster_name}
If you are using Lettuce Client you can use masterSlaveStatefulConnection and pass the sentinel URI it will perform auto discovery in the background and will refresh the master node internally.
https://github.com/lettuce-io/lettuce-core/wiki/Master-Replica
Hi i have create a cluster Redis with sentinel composed by 3 aws instances, i have configured sentinel to have an HA redis cluster and work, but if i simulate a crash of master (shutdown of master instance), sentinel installed on slaves, not locate sentinel of master and the election fail.
My sentinel configuration is:
sentinel monitor master ip-master 6379 2
sentinel down-after-milliseconds master 5000
sentinel failover-timeout master 10000
sentinel parallel-syncs master 1
Same file to all instaces
There are issues when running sentinel on the same node as the master and attempting to trigger a failover. Try it w/o running Sentinel on the master. Ultimately this means not running Sentinel on the same nodes as the Redis instances.
In your case your dead-node simulation is showing why you should not run Sentinel on the same node as Redis: If the node dies you lose one of your sentinels. In theory it should still work but as you and others have seen it isn't certain to work. I have some theories why but I've not yet confirmed them.
In a sense Sentinel is partly a monitoring system. Running a monitoring solution on the same nodes as are being monitored is generally unadvisable anyway, so you should be using off-node sentinels anyway. As Sentinel is resource efficient you don't necessarily need dedicated machines or large VMs. Indeed if you have a static set of application servers (where your client code runs), you should run Sentinel there, keeping in mind you want 3 minimum and a quorum of 50%+1.
recent redis version introduced the "protected-mode" option, which defaults to yes.
with protected-mode set to yes, redis instances, without a password set will not allow remote clients to execute commands.
this also affects sentinels master election.
try it with setting "protected-mode no" in the sentinels. this will allow them to talk to each other.
If you don't want to set protected-mode as no. you'd better set masterauth myredis in redis.conf and use sentinel auth-pass mymaster myredis in sentinel.conf
I'm successfully using Redis for Windows (2.6.8-pre2) in a master slave setup. However, I need to provide some automated failover capability, and it appears the sentinel is the most popular choice. When I run redis in sentinel mode the sentinel connects, but it always thinks the master is down. Also, when I run the sentinel master command it reports that there are 0 slaves (not true) and that there are no other sentinels (again, not true). So it's like it connects to the master, but not correctly.
Has anyone else seen this issue on Windows and, more importantly, is anyone successfully using sentinel in a windows environment? Any help or direction at all is appreciated!
I recommend use this:
1 master node redis server 1 slave node redis server
List item 3 redis sentinels with a quorum of 2
It's so important have more than have 3 sentinels to get a odd quorum.
I made this configuration in Windows 7 and it's working well.
Example of sentinel conf:
port 20001
logfile "sentinel1.log"
sentinel monitor shard1 127.0.0.1 16379 2
sentinel down-after-milliseconds shard1 5000
sentinel failover-timeout shard1 30000