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72 lines
2.5 KiB
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==================================
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Recovering from Monitor Failures
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==================================
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.. index:: monitor, high availability
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In production clusters, we recommend running the cluster with a minimum
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of three monitors. The failure of a single monitor should not take down
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the entire monitor cluster, provided a majority of the monitors remain
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available. If the majority of nodes are available, the remaining nodes
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will be able to form a quorum.
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When you check your cluster's health, you may notice that a monitor
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has failed. For example::
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ceph health
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HEALTH_WARN 1 mons down, quorum 0,2
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For additional detail, you may check the cluster status::
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ceph status
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HEALTH_WARN 1 mons down, quorum 0,2
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mon.b (rank 1) addr 192.168.106.220:6790/0 is down (out of quorum)
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In most cases, you can simply restart the affected node.
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For example::
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service ceph -a restart {failed-mon}
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If there are not enough monitors to form a quorum, the ``ceph``
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command will block trying to reach the cluster. In this situation,
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you need to get enough ``ceph-mon`` daemons running to form a quorum
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before doing anything else with the cluster.
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Client Can't Connect/Mount
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==========================
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Check your IP tables. Some OS install utilities add a ``REJECT`` rule to
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``iptables``. The rule rejects all clients trying to connect to the host except
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for ``ssh``. If your monitor host's IP tables have such a ``REJECT`` rule in
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place, clients connecting from a separate node will fail to mount with a timeout
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error. You need to address ``iptables`` rules that reject clients trying to
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connect to Ceph daemons. For example, you would need to address rules that look
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like this appropriately::
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REJECT all -- anywhere anywhere reject-with icmp-host-prohibited
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You may also need to add rules to IP tables on your Ceph hosts to ensure
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that clients can access the ports associated with your Ceph monitors (i.e., port
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6789 by default) and Ceph OSDs (i.e., 6800 et. seq. by default). For example::
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iptables -A INPUT -m multiport -p tcp -s {ip-address}/{netmask} --dports 6789,6800:6810 -j ACCEPT
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Latency with Down Monitors
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==========================
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When you have a monitor that is down, you may experience some latency as
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clients will try to connect to a monitor in the configuration even though
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it is down. If the client fails to connect to the monitor within a timeout
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window, the client will try another monitor in the cluster.
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You can also specify the ``-m`` option to point to a monitor that is up
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and in the quorum to avoid latency.
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