# SENTINEL: failover aborted - no reachable quorum after master change

- **ID:** `redis/redis-sentinel-down-after-master-failover`
- **Domain:** redis
- **Category:** runtime_error
- **Error Code:** `SENTINEL`
- **Verification:** ai_generated
- **Fix Rate:** 85%

## Root Cause

After a master failover, the new master's configuration epochs are inconsistent, causing sentinel instances to lose quorum and abort the failover process.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| redis 6.2 | active | — | — |
| redis 7.0 | active | — | — |
| redis 7.2 | active | — | — |
| redis 7.4 | active | — | — |

## Workarounds

1. **Manually reset the sentinel state for the affected master: `SENTINEL RESET mymaster` on each sentinel. Then monitor with `SENTINEL MASTER mymaster` to verify quorum.** (85% success)
   ```
   Manually reset the sentinel state for the affected master: `SENTINEL RESET mymaster` on each sentinel. Then monitor with `SENTINEL MASTER mymaster` to verify quorum.
   ```
2. **Force a new failover by running `SENTINEL FAILOVER mymaster` on the leader sentinel after ensuring all sentinels agree on the new master's configuration.** (80% success)
   ```
   Force a new failover by running `SENTINEL FAILOVER mymaster` on the leader sentinel after ensuring all sentinels agree on the new master's configuration.
   ```
3. **Check and synchronize sentinel configuration files across all nodes, ensuring `sentinel monitor` and `sentinel auth-pass` are identical, then restart sentinels one by one.** (90% success)
   ```
   Check and synchronize sentinel configuration files across all nodes, ensuring `sentinel monitor` and `sentinel auth-pass` are identical, then restart sentinels one by one.
   ```

## Dead Ends

- **Restarting all sentinel instances simultaneously** — Simultaneous restart can cause all sentinels to lose state, delaying failover detection and potentially causing split-brain scenarios. (75% fail)
- **Manually setting the old master back as leader** — The old master may be unreachable or have stale data; forcing it back can cause data loss and inconsistency with replicas. (95% fail)
- **Increasing sentinel quorum to 5** — Higher quorum makes it harder to reach consensus, especially in degraded networks, and does not fix the epoch mismatch. (80% fail)