I want to build a redis cluster without replica for testing.
I use cluster create command
redis-cli --cluster create AIP:6379 BIP:6379 CIP:6379
It always become 1 master and 2 replica, not 3 master.
I also tried addnode and cluster meet , and still get 1 master 2 replicas.
Any help?
Related
Is it possible to create a Redis cluster with only 1 master and N slaves/replicas?
I tried it and it failed:
redis-cli --cluster create 127.0.0.1:7000 127.0.0.1:7001 127.0.0.1:7002 --cluster-replicas 2
*** ERROR: Invalid configuration for cluster creation.
*** Redis Cluster requires at least 3 master nodes.
*** This is not possible with 3 nodes and 2 replicas per node.
*** At least 9 nodes are required.
Is there a way to avoid this restriction of minimum 3 masters?
Redis Cluster doesn't support what you are asking for, but there is another H/A Redis mode, "Redis Sentinel":
https://redis.io/docs/manual/sentinel/
This article is worth reading as it illustrates some pros and cons of the two H/A modes:
Redis Sentinel Pros:
With three nodes, you can build up a fully functional Sentinel deployment. (Image 2)
Simplicity - it’s usually simple to maintain and configure.
Highly available, you can build a Redis Sentinel deployment that can survive certain failures without any need for human intervention.
Work as long as a single master instance is available; it can survive the failure of all slave instances.
Multiple slave nodes can replicate data from a master node.
Redis Sentinel Cons:
Not scalable; writes must go to the master, cannot solve the problem of read-write separation.
Slaves may serve reads, but because of asynchronous replication, outdated reads may result.
It doesn’t shard data, so master and slave utilization will be imbalanced.
The slave node is a waste of resources because it does not serve as a backup node.
Redis-Sentinel must be supported by the client. The client holds half of the magic.
I'm trying to create a Redis cluster using an RDB file taken from a single-instance Redis server. Here is what I've tried:
#! /usr/bin/env bash
for i in 6000 6001 6002 6003
do
redis-server --port $i --cluster-config-file "node-$i.cconf" --cluster-enabled yes --dir "$(pwd)" --dbfilename dump.rdb &
done
That script starts up 4 Redis processes that are cluster enabled. It also initializes each node with the dump file.
Then I run redis-trib.rb so that the 4 nodes can find each other:
redis-trib.rb create 127.0.0.1:6000 127.0.0.1:6001 127.0.0.1:6002 127.0.0.1:6003
I get the following error:
>>> Creating cluster
[ERR] Node 127.0.0.1:6060 is not empty. Either the node already knows other nodes (check with CLUSTER NODES) or contains some key in database 0.
I've also tried a variant where only the first node/process is initialized with the RDB file and the others are empty. I can join the 3 empty nodes into a cluster but not the one that's pre-populated with data.
What is the correct way to import a pre-existing RDB file into a Redis cluster?
In case this is an "X-Y problem" this is why I'm doing this:
I'm working on a migration from a single-instance Redis server to an Elasticache Redis Cluster (cluster mode enabled). Elasticache can easily import an RDB file on cluster startup if you upload it to S3. But it takes a long time for an Elasticache cluster to start. To reduce the feedback loop as I test my migration code, I'd like to be able to start a cluster locally also.
I've also tried using the create-cluster utility, but that doesn't appear to have any options to pre-populate the cluster with data.
Hello stack community,
I have a question about Redis sentinel for a specific problem case. I use AWS with Multi AZ to create a sensu cluster.
On eu-central-1a I have a sensu+redis(M), a RBMQ+Sentinel and 2 others Sentinels. Same on eu-central-1b but the redis is my slave on this AZ.
What happen if there is a problem and eu-central-1a can not communicate with eu-central-1b ? What I think is that Sentinel on eu-central-1b should promote my redis slave to master, because he can not contact my redis master. So I should have 2 redis masters running together on 2 different AZ.
But when the link is retrieved between AZ, I will still have 2 masters, with 2 different datas. What will happen in this case ? One master will become a slave and data will be replicated without loss ? Do we need to restart a master and he will be a slave ?
Sentinel detects changes to the master for example
If the master goes down and is unreachable a new slave is elected. This is based on the quorum where multiple sentinels agree that the master has gone down. The failover then occurs.
Once the sentinel detects the master come back online it is then a slave I believe thus the new master continues I believe. You will loose data in the switchover from master to new master that in inevitable.
If you loose connection then yes sentinel wont work correctly as it relies on multiple sentinels to agree the master redis is down. You shouldn't use sentinel in a 2 sentinel system.
Basic solution would be for you to put a extra sentinel on another server maybe the client/application server that isn't running redis/sentinel this way you can make use of the quorum and sentinels agreeing the master is down.
Does it require sentinel to monitor each master in the cluster with a distinct service name, or just one of the 3 masters in the cluster?
My current config is 3 masters, 3 slaves, and 3 sentinel instances. Each instance of sentinel is monitoring each master. master1, master2, master3. I haven't seen any documentation that has more than a single master, and the redis documentation isn't real clear.
I found the solution by running a test myself. Yes, in a cluster configuration you need to monitor each master in order for failover to occur.
Suppose I have [Slave IP Address] which is the slave of [Master IP Address].
Now my master server has been shut down, and I need to set this slave to be master MANUALLY (WITHOUT using sentinel automatic failover, WITH redis command).
Is it possible doing this without restarting the redis service ? (and losing all the cached data)
use SLAVEOF NO ONE to promote a slave to master
http://redis.io/commands/slaveof
it depends, if you are in a cluster you will be better using the fail over. You will need to use the force option in the command
http://redis.io/commands/cluster-failover
Is it possible doing this without restarting the redis service? (and
losing all the cached data)
yes that's possible, you can use
SLAVEOF NO ONE (without sentinel)
But it is recommended to use sentinel to avoid data loss.
sentinel failover master-name(with sentinel)
This will force the sentinel to switch master.
The new master will have all the data that was synchronized before the old-master shutdown.
Redis will automatically choose the best slave with max. data, that will reduce the amount of data we lose when switching master.
Below 2 options in step 3 have helped me to recover the cluster once a master node is down, compute was replaced or other not recoverable state.
1 .- First you need to connect to the slave node, use redis-cli, here a link how to do that: How to connect to remote Redis server?
2 .- Once connected to the slave node run the command cluster nodes to validate master node is in fail state, also run cluster info to see the overall state of your cluster(this is always a good idea)
3 .- Inside the slave node to be promoted run command: cluster failover,
in rare cases when there is some serious issues with redis this
command could fail, and you will need to use cluster failover force
or cluster failover takeover, here more info abut the implications
of those options: https://redis.io/commands/cluster-failover
4 .- Run cluster forged $old_master_id in all your cluster nodes
5 .- Add a new node with cluster meet $new_node_IP $new_node_PORT
6 .- Subscribe your new node to your brand new master, login in to the new bode and run cluster replicate $master_node_id
Steps 1-3 are required for the slave-master promotion and 4-5 are required to left all cluster in a healthy master-slave equilibrium.
As of Redis version 5.0.0 the SLAVEOF command is regarded as deprecated.
If a Redis server is already acting as replica, the command REPLICAOF NO ONE will turn off the replication, turning the Redis server into a MASTER.