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Error: redis slave cannot connect to master

What's Causing This Error

The error 'redis slave cannot connect to master' typically occurs due to one of the following reasons:

  1. Network Issues: There may be connectivity issues between the master and slave instances. This can be due to firewall rules, incorrect IP addresses or ports, network latency, or outages that are causing the slave instance to be unable to reach the master.

  2. Configuration Errors: If configuration settings for Redis replication in the master or slave are incorrect, they could cause this error. For example, if the slaveof directive in the slave's configuration is incorrectly set, it won't be able to connect to its master.

  3. Incompatible Redis Versions: If you're trying to replicate from a higher version master to a lower version slave, some compatibility issues might occur leading to connection failures.

Solution - Here's How To Resolve It

Follow these steps to resolve the 'redis slave cannot connect to master' error:

Step 1: Check Network Connectivity

Use tools like ping, telnet, or nc to verify the network connectivity between the master and slave. Ensure that there's no firewall blocking the connection and that the correct IP address and port are being used.

Step 2: Verify Configuration Settings

Check the configuration files on both the master and slave instances. In the case of the slave, ensure that the slaveof directive is correctly set with the master's IP address and port. On the master, ensure that it's configured to accept connections from slaves.

Step 3: Confirm Redis Version Compatibility

Check the versions of Redis running on the master and slave servers. If they are incompatible (master is a higher version than the slave), consider upgrading the Redis version on the slave or downgrading on the master to ensure compatibility.

Step 4: Check Error Logs

Both Redis master and slave instances have logs that may provide more details about the connection problem. Monitor these logs for any additional error messages that could help in troubleshooting.

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Dragonfly is fully compatible with the Redis ecosystem and requires no code changes to implement.