Error: redis slave not becoming master

What's Causing This Error

There can be several reasons behind the error "redis slave not becoming master":

1. Network Issues: Connectivity issues between the master and the slave could prevent a successful failover process. This might happen due to firewall rules, network latency, or other networking conditions.

2. Configuration Problems: Incorrectly configured Redis instances or failover settings can lead to this issue. For example, incorrectly set slave-priority or min-slaves-to-write parameters.

3. Persistence Mechanisms: If the Redis instance persistence mechanism (RDB or AOF) is incorrectly set up or failing, it can interfere with the role change.

4. Resource Limitations: Lack of system resources like memory or CPU can cause issues with the failover process.

Solution - Here's How To Resolve It

To resolve the "redis slave not becoming master" error, follow these steps:

1. Check Network Connectivity: Ensure there are no connectivity issues between your Redis instances. Tools like ping, traceroute, or even Redis's own PING command can help diagnose network problems.

2. Correct Configurations: Check your Redis configurations ensuring properties such as slave-priority and min-slaves-to-write are correctly set. The CONFIG GET command can be used to check these settings.

3. Review Persistence Settings: Verify your persistence settings. Remember to regularly save your RDB backup and ensure AOF is properly configured if you're using it for persistence.

4. Monitor Resources: Monitor the resource usage of your Redis instances. If resources are constantly maxed out, consider upgrading your server or optimizing your application.

5. Redis Logs: Review the Redis logs for any indicators or warnings about why the failover didn't occur as expected.

6. Test Failover: Conduct a manual failover test using the CLUSTER FAILOVER command (for clustered mode) or by manually promoting a slave to master. This can help you understand if there's an issue with your setup.