Ceph is a powerful and flexible solution for distributed storage, but like any complex tool, it is not exempt from errors that are difficult to diagnose. If you get the message “could not connect to ceph cluster despite configured monitors”, you know that something is wrong with your cluster. And no, it’s not that the monitors are asleep. This error is more common than it seems, especially after network changes, reboots or when someone has touched the configuration “just a little bit”.
In this article we get to the point: we tell you the real causes behind this problem and most importantly, how to fix it without losing your data or your sanity in the process.
When Ceph tells you that it cannot connect to the cluster “despite configured monitors”, what is really happening is that the client or daemon can see the configuration of the monitors, but cannot establish communication with any of them. It’s like being ghosting, no matter how much you call, they don’t pick it up.
Ceph monitors are the brains of the cluster: they maintain the topology map, manage authentication, and coordinate global state. Without connection to the monitors, your Ceph cluster is basically a bunch of expensive disks with no functionality.
The number one cause is usually the network. Either because of misconfigured firewalls, IP changes or routing problems.
Rapid diagnosis:
# Verifica conectividad básica
telnet [IP_MONITOR] 6789
# o con netcat
nc -zv [IP_MONITOR] 6789
# Comprueba las rutas
ip route show
Solution:
firewall-cmd --permanent --add-service=ceph-mon
firewall-cmd --reload
If you have changed node IPs or modified the network configuration, it is likely that the monmap (monitor map) is obsolete.
Diagnosis:
# Revisa el monmap actual
ceph mon dump
# Compara con la configuración
cat /etc/ceph/ceph.conf | grep mon_host
Solution:
# Extrae un monmap actualizado de un monitor funcionando
ceph mon getmap -o monmap_actual
# Inyecta el monmap corregido en el monitor problemático
ceph-mon -i [MON_ID] --inject-monmap monmap_actual
Ceph monitors are very strict with time synchronization. An offset of more than 50ms can cause this error.
Diagnosis:
# Verifica el estado de NTP/chrony
chrony sources -v
# o con ntpq
ntpq -p
# Comprueba el skew entre nodos
ceph status
Solution:
# Configura chrony correctamente
systemctl enable chronyd
systemctl restart chronyd
# Si tienes servidores NTP locales, úsalos
echo "server tu.servidor.ntp.local iburst" >> /etc/chrony.conf
If the monitors have suffered data corruption or are in an inconsistent state, they may not respond correctly.
Diagnosis:
# Revisa los logs del monitor
journalctl -u ceph-mon@[MON_ID] -f
# Verifica el estado del almacén del monitor
du -sh /var/lib/ceph/mon/ceph-[MON_ID]/
Solution:
# Para un monitor específico, reconstruye desde los OSDs
systemctl stop ceph-mon@[MON_ID]
rm -rf /var/lib/ceph/mon/ceph-[MON_ID]/*
ceph-objectstore-tool --data-path /var/lib/ceph/osd/ceph-0 --journal-path /var/lib/ceph/osd/ceph-0/journal --type bluestore --op update-mon-db --mon-store-path /tmp/mon-store
ceph-mon --mkfs -i [MON_ID] --monmap /tmp/monmap --keyring /tmp/ceph.mon.keyring
Sometimes the problem is on the client side: outdated configuration, incorrect keys or poorly defined parameters.
Diagnosis:
# Verifica la configuración del cliente
ceph config show client
# Comprueba las claves de autenticación
ceph auth list | grep client
Solution:
# Regenera las claves de cliente si es necesario
ceph auth del client.admin
ceph auth get-or-create client.admin mon 'allow *' osd 'allow *' mds 'allow *' mgr 'allow *'
# Actualiza la configuración
ceph config dump > /etc/ceph/ceph.conf
This error can escalate quickly if not handled correctly. If you find yourself in any of these situations, it’s time to stop and seek professional help:
Ceph clusters in production are not trial and error territory. One false move can turn a connectivity problem into a data loss.
To avoid encountering this error in the future:
Proactive monitoring:
Best practices:
Regular testing:
Distributed storage clusters such as Ceph require specific expertise to function optimally. If you have encountered this error and the above solutions do not solve your problem, or if you simply want to ensure that your Ceph infrastructure is properly configured and optimized, we can help.
Our team has experience solving complex Ceph problems in production environments, from urgent troubleshooting to performance optimization and high availability planning.
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