红帽全球峰会27.2. Configuring a quorum device
Configure a quorum device and add it to the cluster with the following procedure.
In this example:
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The node used for a quorum device is
qdevice. The quorum device model is
net, which is currently the only supported model. Thenetmodel supports the following algorithms:-
ffsplit: fifty-fifty split. This provides exactly one vote to the partition with the highest number of active nodes. lms: last-man-standing. If the node is the only one left in the cluster that can see theqnetdserver, then it returns a vote.警告The LMS algorithm allows the cluster to remain quorate even with only one remaining node, but it also means that the voting power of the quorum device is great since it is the same as number_of_nodes - 1. Losing connection with the quorum device means losing number_of_nodes - 1 votes, which means that only a cluster with all nodes active can remain quorate (by overvoting the quorum device); any other cluster becomes inquorate.
For more detailed information about the implementation of these algorithms, see the
corosync-qdevice(8) man page on your system.
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The cluster nodes are
node1andnode2.
Procedure
On the node that you will use to host your quorum device, configure the quorum device with the following command. This command configures and starts the quorum device model
netand configures the device to start on boot.[root@qdevice:~]# pcs qdevice setup model net --enable --start Quorum device 'net' initialized quorum device enabled Starting quorum device... quorum device startedAfter configuring the quorum device, you can check its status. This should show that the
corosync-qnetddaemon is running and, at this point, there are no clients connected to it. The--fullcommand option provides detailed output.[root@qdevice:~]# pcs qdevice status net --full QNetd address: *:5403 TLS: Supported (client certificate required) Connected clients: 0 Connected clusters: 0 Maximum send/receive size: 32768/32768 bytesEnable the ports on the firewall needed by the
pcsddaemon and thenetquorum device by enabling thehigh-availabilityservice onfirewalldwith following commands.[root@qdevice:~]# firewall-cmd --permanent --add-service=high-availability [root@qdevice:~]# firewall-cmd --add-service=high-availabilityFrom one of the nodes in the existing cluster, authenticate user
haclusteron the node that is hosting the quorum device. This allowspcson the cluster to connect topcson theqdevicehost, but does not allowpcson theqdevicehost to connect topcson the cluster.[root@node1:~] # pcs host auth qdevice Username: hacluster Password: qdevice: AuthorizedAdd the quorum device to the cluster.
Before adding the quorum device, you can check the current configuration and status for the quorum device for later comparison. The output for these commands indicates that the cluster is not yet using a quorum device, and the
Qdevicemembership status for each node isNR(Not Registered).[root@node1:~]# pcs quorum config Options:[root@node1:~]# pcs quorum status Quorum information ------------------ Date: Wed Jun 29 13:15:36 2016 Quorum provider: corosync_votequorum Nodes: 2 Node ID: 1 Ring ID: 1/8272 Quorate: Yes Votequorum information ---------------------- Expected votes: 2 Highest expected: 2 Total votes: 2 Quorum: 1 Flags: 2Node Quorate Membership information ---------------------- Nodeid Votes Qdevice Name 1 1 NR node1 (local) 2 1 NR node2The following command adds the quorum device that you have previously created to the cluster. You cannot use more than one quorum device in a cluster at the same time. However, one quorum device can be used by several clusters at the same time. This example command configures the quorum device to use the
ffsplitalgorithm. For information about the configuration options for the quorum device, see thecorosync-qdevice(8) man page on your system.[root@node1:~]# pcs quorum device add model net host=qdevice algorithm=ffsplit Setting up qdevice certificates on nodes... node2: Succeeded node1: Succeeded Enabling corosync-qdevice... node1: corosync-qdevice enabled node2: corosync-qdevice enabled Sending updated corosync.conf to nodes... node1: Succeeded node2: Succeeded Corosync configuration reloaded Starting corosync-qdevice... node1: corosync-qdevice started node2: corosync-qdevice startedCheck the configuration status of the quorum device.
From the cluster side, you can execute the following commands to see how the configuration has changed.
The
pcs quorum configshows the quorum device that has been configured.[root@node1:~]# pcs quorum config Options: Device: Model: net algorithm: ffsplit host: qdeviceThe
pcs quorum statuscommand shows the quorum runtime status, indicating that the quorum device is in use. The meanings of of theQdevicemembership information status values for each cluster node are as follows:-
A/NA- The quorum device is alive or not alive, indicating whether there is a heartbeat betweenqdeviceandcorosync. This should always indicate that the quorum device is alive. -
V/NV-Vis set when the quorum device has given a vote to a node. In this example, both nodes are set toVsince they can communicate with each other. If the cluster were to split into two single-node clusters, one of the nodes would be set toVand the other node would be set toNV. MW/NMW- The internal quorum device flag is set (MW) or not set (NMW). By default the flag is not set and the value isNMW.[root@node1:~]# pcs quorum status Quorum information ------------------ Date: Wed Jun 29 13:17:02 2016 Quorum provider: corosync_votequorum Nodes: 2 Node ID: 1 Ring ID: 1/8272 Quorate: Yes Votequorum information ---------------------- Expected votes: 3 Highest expected: 3 Total votes: 3 Quorum: 2 Flags: Quorate Qdevice Membership information ---------------------- Nodeid Votes Qdevice Name 1 1 A,V,NMW node1 (local) 2 1 A,V,NMW node2 0 1 QdeviceThe
pcs quorum device statusshows the quorum device runtime status.[root@node1:~]# pcs quorum device status Qdevice information ------------------- Model: Net Node ID: 1 Configured node list: 0 Node ID = 1 1 Node ID = 2 Membership node list: 1, 2 Qdevice-net information ---------------------- Cluster name: mycluster QNetd host: qdevice:5403 Algorithm: ffsplit Tie-breaker: Node with lowest node ID State: ConnectedFrom the quorum device side, you can execute the following status command, which shows the status of the
corosync-qnetddaemon.[root@qdevice:~]# pcs qdevice status net --full QNetd address: *:5403 TLS: Supported (client certificate required) Connected clients: 2 Connected clusters: 1 Maximum send/receive size: 32768/32768 bytes Cluster "mycluster": Algorithm: ffsplit Tie-breaker: Node with lowest node ID Node ID 2: Client address: ::ffff:192.168.122.122:50028 HB interval: 8000ms Configured node list: 1, 2 Ring ID: 1.2050 Membership node list: 1, 2 TLS active: Yes (client certificate verified) Vote: ACK (ACK) Node ID 1: Client address: ::ffff:192.168.122.121:48786 HB interval: 8000ms Configured node list: 1, 2 Ring ID: 1.2050 Membership node list: 1, 2 TLS active: Yes (client certificate verified) Vote: ACK (ACK)
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