Redis readonly you cant write against a read only replica

sentinel cluster and redis on it, when there is change to the master, this issue happen, you cannot solve it 100%, On practice, you need to ensure that redis client is able to tolerate the failure, work on safe mode, on certain exceptions it may retry few attempts before giving up or make it up. To know who is master, ask sentinel, to check master readyness, use HA proxy, https://www.haproxy.com/blog/haproxy-advanced-redis-health-check/

Ankit Gupta

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Dec 14, 2021, 6:37:45 AM12/14/21

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Hi Experts,

We are using redis version 5.x, and using sentinel based architecture.

Below is the setup

N1(M)

/         \

/             \

N2(S)         N3(S)

N1 got crashed  , and due to failover N3 was promoted as a new master. After sometime when N1 was recovered & joined the setup/cluster as slave it requested for a full re-synchronization from N3(present master) due to which BGSave was invoked. 

During this process any request on master , was giving below error:

org.springframework.data.redis.connection.RedisPipelineException: Pipeline contained one or more invalid commands; nested exception is org.springframework.dao.InvalidDataAccessApiUsageException: READONLY You can't write against a read only replica.; nested exception is redis.clients.jedis.exceptions.JedisDataException: READONLY You can't write against a read only replica.

We have few queries around this

1. Are we getting this error because master was busy in serving any other request?

2. Is there a configuration we can do so that if another slave is already connected then new node should do sync from existing slave?

3. Is this the expected behaviour?

Thanks in advance.

-Ankit

Vivek Mishra

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Jul 22, 2022, 1:13:25 PMJul 22

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In my case i set REDIS_HOST to the service redis-headless and it worked

Ankit Gupta

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Aug 28, 2022, 7:46:54 AMAug 28

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Hi All,

We received this error again in our production setup.  Surprisingly there's nothing revealed in the redis.log or even in sentinel.log.  

If someone has someone faced similar issue, then you're help on this much appreciated.

Ankit Gupta

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Aug 28, 2022, 7:48:00 AMAug 28

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Hi Vivek,

Has the issue resolved after this fix ?

Can you please share the steps that you followed for this ?

On Saturday, July 23, 2022 at 1:43:25 AM UTC+5:30 Vivek Mishra wrote:

Ankit Gupta

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Sep 4, 2022, 10:19:59 PMSep 4

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Hi Team,

Has anyone faced such an issue. Can this be an issue with # of connections or sentinel overload or client library ?

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