RedisReplicaLinkDown

A Redis replica has been disconnected from its master for several minutes and is no longer receiving updates.


Severity	critical
Source	oliver006/redis_exporter 1.50+
Key metric	`redis_master_link_up` (1 = `master_link_status:up`)

What it means

On a replica, INFO replication reports whether the link to the master is up. The alert fires when it has stayed down for several minutes, longer than a normal reconnect or short resync.

While the link is down, the replica serves increasingly stale reads, and it is not a safe failover target: promoting it would lose everything written since the link dropped. If this replica is your only one, you have no redundancy.

Common causes

The master is down or was replaced, and the replica still points at the old address.
A full resync loops: the replica requests a full sync, the RDB transfer takes too long, and the master drops it because client-output-buffer-limit replica is exceeded.
The replication backlog (repl-backlog-size) is too small, so every short disconnect forces a full sync.
Wrong masterauth after a password or ACL change.
Network policy, firewall or DNS change between replica and master.

First checks

On the replica, look at link state and how long it has been down:

redis-cli -h <replica> INFO replication | grep -E '^(role|master_host|master_port|master_link_status|master_link_down_since_seconds|master_sync_in_progress)'

On the master, check whether it sees the replica:
```
redis-cli -h <master> INFO replication
```
Read the replica log for the reason sync fails (auth errors, timeouts, “MASTER aborted replication”):
```
kubectl -n <ns> logs <replica-pod> --tail=100 | grep -iE 'master|sync|replica'
```

Check the master log for output buffer disconnects:

kubectl -n <ns> logs <master-pod> --tail=200 | grep -i 'scheduled to be closed ASAP for overcoming of output buffer limits'

Find all affected replicas:
```
redis_master_link_up == 0
```

Fixing it

If the master moved, run REPLICAOF <new-master> <port> (or let Sentinel reconfigure it). If full syncs keep failing, raise the replica output buffer limit and repl-backlog-size on the master with CONFIG SET, and persist the change to the config. Fix masterauth after credential changes, and check connectivity with redis-cli -h <master> PING from the replica host.

RedisReplicasDisconnected: the master’s view of lost replicas.
RedisMissingMaster: the link may be down because there is no master.
RedisDown: check whether the master itself is unreachable.