You can't write against a read only replica

[Ankit Gupta]

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]

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

[Ankit Gupta]

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]

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]

Hi Team,

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