Redis MASTER_TIMEOUT No reply from the master

The replica did not receive a reply from the master within the configured timeout period.

When you encounter the MASTER_TIMEOUT error in Redis, indicating that a replica has not been able to communicate with its master for a certain period, you can take the following immediate actions for investigation:

  1. Check the Network Connectivity: Ensure that the network connection between the master and the replica is stable. You can use the ping command to check the network connectivity to the master's IP address.
  2. ping <master_ip_address>
  3. Review Redis Logs: Look for any error messages or warnings in the Redis logs that might indicate what caused the communication failure. The logs could provide hints such as high latency, network issues, or configuration problems.
  4. tail -f /var/log/redis/redis-server.log
  5. Check Redis Server Status: Use the INFO replication command on both the master and replica instances to check their status. This command will show you the state of replication and if the replica is connected to the master.
  6. redis-cli -h <host> -p <port> INFO replication
  7. Verify Configuration Settings: Ensure that the repl-timeout setting on the replica is not too low. It's possible that network latency or spikes in traffic are causing the timeout. You can check this setting with:
  8. redis-cli -h <replica_host> -p <replica_port> CONFIG GET repl-timeout
  9. Examine System Metrics: Look at system-level metrics for both the master and the replica, such as CPU, memory usage, and network throughput. High resource utilization might be impacting the Redis instances' ability to communicate effectively.
  10. Depending on your environment, you might use commands like top, htop, netstat, or tools like iftop or nmon for real-time monitoring.
  11. Test Redis Command Latency: You can use the redis-cli --latency command to monitor latency in real-time between the replica and the master. This can help identify if there are significant network delays affecting communication.
  12. redis-cli -h <master_host> -p <master_port> --latency

Following these steps should help you identify the root cause of the MASTER_TIMEOUT error.

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