How to manage and maintain RHCs cluster


Management and maintenance of RHCs cluster is a very complex and tedious work. In order to maintain a RHCs cluster well, we must be familiar with the basic operation principle of RHCs. In terms of cluster management, RHCs provides two methods: Luci graphical interface mode and command line mode. Here we focus on how to manage RHCs cluster under the command line.

Start RHCs cluster

The core processes of RHCs cluster are cman and rgmanager. To start the cluster, start cman, then rgmanager, as follows:

Start the cluster service on the host web1:

[[email protected] ~]# service cman start
Starting cluster:
     Loading modules... done
     Mounting configs... done
     Starting ccsd... done
     Starting cman... done
     Starting qdiskd...done
     Starting daemons...done
     Starting fencing... done
[ OK ]

After cman starts successfully in other nodes, start rgmanager service. The specific operations are as follows:

[[email protected] ~]# service rgmanager start
Starting Cluster Service Manager: [ OK ]

Shut down RHCs cluster

As opposed to starting the cluster server, the command to shut down the RHCs cluster is as follows:

[[email protected] ~]# service rgmanager stop
[[email protected] ~]# service cman stop

Sometimes when shutting down cman service, it may prompt failure. At this time, you can check whether the local shared storage gfs2 file system has been uninstalled, or check whether all rgmanager services of other nodes have been shut down normally.

Manage application services

After the cluster system is started, the application service is started automatically by default. However, if an application service is not started automatically, it needs to be started manually. The commands to manage application services are clusvcadm, through which you can start, close, restart and switch the Dell application services in the cluster services.

Start an application

You can start the application service on a node in the following ways, for example, starting wrbserver:

[[email protected] ~]#clusvcadm -e webserver -m web1
Member web1 trying to enable service:webserver...Success
service:webserver is now running on web1

Close an application

You can shut down the application service on a node in the following ways to start mysqlserver as an example:

[[email protected] ~]#clusvcadm -s mysqlserver -m web1
Member mysql1 stopping service:mysqlserver...Success

Restart an application

You can restart the application service on a node in the following ways to start wrbserver as an example:

[[email protected] ~]#clusvcadm -R wrbserver -m web1
Member web1 trying to restart service:wrbserver...Success

This command is executed on the web2 node, and it can also restart the wrbserver on the web1 node. It can be seen that the clusvcadm command can be executed on any node in the cluster.

Switch an application

You can switch the application services on a node in the following ways, for example, to switch the services on node web1 to node web2:

[[email protected] ~]# clusvcadm -r wrbserver -m web2
Trying to relocate service:webserver to web2...Success
service:webserver is now running on web2

Monitoring RHCs cluster status

Through the monitoring of RHCs, it is helpful to understand the health status of each node in the cluster, find problems and solve them in time. The RHCs cluster provides a wealth of status view commands. Here we mainly introduce the usage of cman tool, clustat and CCS tool.

Cman? Tool command

There are many parameters of cman tool, but the method of using them is simple. Here are two methods of using them:

[[email protected] ~]# cman_tool  nodes -a
Node  Sts   Inc   Joined               Name
   0   M      0   2010-08-23 01:24:00  /dev/sdb7
   1   M   2492   2010-08-23 01:22:43  web2
   2   M   2492   2010-08-23 01:22:43  Mysql1
   3   M   2492   2010-08-23 01:22:43  Mysql2
   4   M   2488   2010-08-23 01:22:43  web1

This command shows the node name, the corresponding node IP address and the time of joining the cluster.

If you want to learn more about cluster nodes, you can use the following command:

[[email protected] ~]# cman_tool   status
Version: 6.2.0
Config version: 35 cluster profile version number
Cluster name: mycluster
Cluster Id: 56756
Cluster Member: Yes
Cluster Generation: 2764
Membership state: Cluster-Member
Nodes: 4 cluster nodes
Expected votes: 6 × expected votes
Quorum device votes: 2 ා vote disk vote value
Total votes: 6 × size of all votes in the cluster
Quorum: 4 ා the legal voting value of the cluster. If it is lower than this value, the cluster will stop service
Active subsystems: 9 
Flags: Dirty 
Ports Bound: 0 177  
Node name: web1
Node ID: 4 the ID number of the node in the cluster
Multicast addresses: cluster broadcast address 
Node addresses: - the corresponding IP address of this node

Clustat command

The clustat command is very simple to use. For detailed usage, you can get help information through “clustat – H”. Here are just a few examples.

[[email protected] ~]#clustat  -i 3
Cluster Status for mycluster @ Mon Aug 23 18:54:15 2010
Member Status: Quorate
Member Name              ID                        Status
 ------ ----            ----                       ------
 web2                     1                    Online, rgmanager
 Mysql1                   2                    Online, rgmanager
 Mysql2                   3                    Online, rgmanager
 web1                     4                    Online, Local, rgmanager
 /dev/sdb7                0                    Online, Quorum Disk
 Service Name             Owner (Last)         State         
 ------- ----             ----- ------         --------         
 service:mysqlserver      Mysql1               started       
 service:webserver        web1                 started

The meaning of output content is as follows:

The “- I” parameter of clustat can display the running status of each node and service in the cluster system in real time. “- I 3” indicates that the cluster status is refreshed every three seconds.

In this output, you can see that each node is in “online” state, indicating that each node is running normally. If a node exits the cluster, the corresponding state should be “offline”. At the same time, you can see that the two services of the cluster are also in “started” state, running in mysql1 node and web1 node respectively.

In addition, you can know the corresponding relationship of cluster nodes through the “Id” column. For example, web2 corresponds to the “node 1” node in this cluster. Similarly, web1 corresponds to the “node 4” node. Understanding the order of cluster nodes is helpful to the interpretation of cluster logs.

CCS? Tool command

CCS tool is mainly used to manage cluster configuration file cluster.conf. Through CCS tool, you can add / delete nodes, add / delete fence devices, update cluster configuration files and other operations in the cluster.

Here are some application examples of CCS tool:

After modifying the configuration file in one node, you can execute the “CCS? Tool update” command to update the configuration file in all nodes, for example:

[[email protected] cluster]# ccs_tool  update /etc/cluster/cluster.conf
Proposed updated config file does not have greater version number.
  Current config_version :: 35
  Proposed config_version:: 35
Failed to update config file.

CCS tool determines whether to update or not according to the “config” value in cluster.conf. Therefore, after modifying the cluster.conf file, you must update the config “version” value of cluster.conf, so that the configuration file can be updated when CCS tool is executed.

[[email protected] cluster]# ccs_tool  update /etc/cluster/cluster.conf
Config file updated from version 35 to 36
Update complete.

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