Redis Sentinel — quorum not met for failover
Redis Sentinel cannot failover because the number of available sentinels is less than the configured quorum, leaving the cluster without a new master.
Symptoms
- +sdown master mymaster (sentinels cannot agree)
- No failover initiated despite master being down
- Error: Not enough sentinels to reach quorum
Possible causes
- Fewer than quorum sentinels are reachable due to network partition
- Sentinel instances are down or misconfigured
- The quorum value is set higher than the number of deployed sentinels
Diagnosis steps
Check sentinel status
redis-cli -p 26379 sentinel mastersInterpretation
Shows the master state and the number of sentinels that agree.
Count reachable sentinels
redis-cli -p 26379 sentinel sentinels mymasterInterpretation
Lists all sentinels monitoring the master; compare count against quorum.
Root cause
Sentinel failover requires a quorum of sentinels to agree the master is down; if fewer than quorum sentinels are reachable, no failover is initiated.
Fix
Ensure at least quorum sentinels are deployed and reachable, reduce the quorum to match available sentinels, or restore network connectivity between sentinel instances.
Verify the fix
Shut down the master and confirm Sentinel promotes a replica within the expected failover time.
Symptom walkthrough
Redis Sentinel cannot failover because the number of available sentinels is less than the configured quorum, leaving the cluster without a new master. The error appears in production but may not surface in local development because the conditions that trigger it depend on the deployment environment or runtime configuration. Understanding the full symptom set helps distinguish this issue from similar errors.
Diagnosis in practice
Follow the diagnosis steps in the frontmatter to isolate the cause. Each step includes a command and an interpretation of the output. The goal is to narrow down whether the issue is in the configuration, the runtime, or the application code. Reproduce the error in a minimal setup before applying a fix.
Root cause
Sentinel failover requires a quorum of sentinels to agree the master is down; if fewer than quorum sentinels are reachable, no failover is initiated.
Fix
Ensure at least quorum sentinels are deployed and reachable, reduce the quorum to match available sentinels, or restore network connectivity between sentinel instances. After applying the fix, monitor the system to confirm the error does not recur under load or in different environments.
Verification
Shut down the master and confirm Sentinel promotes a replica within the expected failover time. If the verification passes, the fix is confirmed; if not, re-examine the diagnosis steps for missed contributing factors.
Diagnostic commands
Run these commands to reproduce and diagnose the issue:
redis-cli -p 26379 sentinel masters
redis-cli -p 26379 sentinel sentinels mymaster