Managing High-Availability Clusters

This section presents step-by-step procedures for performing a variety of administrative tasks for a high-availability cluster:

• Connecting Brokers into a High-Availability Cluster

• Adding and Removing Brokers in a High-Availability Cluster

• Preventing or Forcing Broker Failover

• Converting a Standalone Data Store to a Shared Data Store

• Backing up a Shared Data Store

Connecting Brokers into a High-Availability Cluster

Because high-availability clusters are self-configuring, there is no need to explicitly specify the list of brokers to be included in the cluster. Instead, all that is needed is to set each broker’s configuration properties appropriately and then start the broker; as long as its properties are set properly, it will automatically be incorporated into the cluster. High-Availability Cluster Properties describes the required properties, which include vendor-specific JDBC database properties.

In addition to creating a high-availability cluster as described in this section, you must also configure clients to successfully reconnect to a failover broker in the event of broker or connection failure. You do this by setting the imqReconnectAttempts connection factory attribute to a value of -1.

The property values needed for brokers in a high-availability cluster can be set separately in each broker’s instance configuration file, or they can be specified in a cluster configuration file that all the brokers reference. The procedures are as follows:

To Connect Brokers Using a Cluster Configuration File

An alternative method, better suited for production systems, is to use a cluster configuration file to specify the composition of the cluster:

1. Create a cluster configuration file specifying the cluster’s high-availability-related configuration properties.

   High-Availability Cluster Properties shows the required property values. However, do not include the imq.brokerid property in the cluster configuration file; this must be specified separately for each individual broker in the cluster.

2. Specify any additional, vendor-specific properties that might be needed.

   The vendor-specific properties required for MySQL and HADB are shown in Example 8–1 and Example 8–2, respectively.

3. For each broker in the cluster:

   1. Start the broker with the imqbrokerd command.

      The first time a broker instance is run, an instance configuration file (config.properties) is automatically created.

   2. Shut down the broker.

      Use the imqcmd shutdown bkr command.

   3. Edit the instance configuration file to specify the location of the cluster configuration file.

      In the broker’s instance configuration file, set the imq.cluster.url property to point to the location of the cluster configuration file you created in step 1.

   4. Specify the broker identifier.

      Set the imq.brokerid property in the instance configuration file to the broker’s unique broker identifier. This value must be different for each broker.

4. Place a copy of, or a symbolic link to, your JDBC driver’s .jar file in the Message Queue external resource files directory, depending on your platform (see Appendix A, Platform-Specific Locations of Message Queue Data):

   Solaris: /usr/share/lib/imq/ext

   
   

   Linux: /opt/sun/mq/share/lib/ext

   
   

   Windows: IMQ_VARHOME\lib\ext

   
   

5. Create the database schema needed for Message Queue persistence.

   Use the imqdbmgr create tbl command; see Database Manager Utility.

6. Restart each broker with the imqbrokerd command.

   The brokers will automatically register themselves into the cluster on startup.

To Connect Brokers Using Instance Configuration Files

1. For each broker in the cluster:

   1. Start the broker with the imqbrokerd command.

      The first time a broker instance is run, an instance configuration file (config.properties) is automatically created.

   2. Shut down the broker.

      Use the imqcmd shutdown bkr command.

   3. Edit the instance configuration file to specify the broker’s high-availability-related configuration properties.

      High-Availability Cluster Properties shows the required property values.

   4. Specify any additional, vendor-specific properties that might be needed.

      The vendor-specific properties required for MySQL and HADB are shown in Example 8–1 and Example 8–2, respectively.

2. Place a copy of, or a symbolic link to, your JDBC driver’s .jar file in the Message Queue external resource files directory, depending on your platform (see Appendix A, Platform-Specific Locations of Message Queue Data):

   Solaris: /usr/share/lib/imq/ext

   
   

   Linux: /opt/sun/mq/share/lib/ext

   
   

   Windows: IMQ_VARHOME\lib\ext

   
   

3. Create the database schema needed for Message Queue persistence.

   Use the imqdbmgr create tbl command; see Database Manager Utility.

4. Restart each broker with the imqbrokerd command.

   The brokers will automatically register themselves into the cluster on startup.

Adding and Removing Brokers in a High-Availability Cluster

Because high-availability clusters are self-configuring, the procedures for adding and removing brokers are simpler than for a conventional cluster.

To Add a New Broker to a High-availability Cluster

1. Set the new broker’s high-availability-related properties, as described in the preceding section.

   You can do this either by specifying the individual properties in the broker’s instance configuration file (config.properties) or, if there is a cluster configuration file, by setting the broker’s imq.cluster.url property to point to it.

2. Start the new broker with the imqbrokerd command.

   The broker will automatically register itself into the cluster on startup.

To Remove a Broker from a high-availability Cluster

1. Make sure the broker is not running.

   If necessary, use the command

      imqcmd shutdown bkr
   

   to shut down the broker.

2. Remove the broker from the cluster with the command

      imqdbmgr remove bkr
   

   This command deletes all database tables for the corresponding broker.

Preventing or Forcing Broker Failover

Although the takeover of a failed broker’s persistent data by a failover broker in a high-availability cluster is normally automatic, there may be times when you want to prevent such failover from occurring. To suppress automatic failover when shutting down a broker, use the -nofailover option to the imqcmd shutdown bkr subcommand:

   imqcmd shutdown bkr  -nofailover  -b hostName:portNumber

where hostName and portNumber are the host name and port number of the broker to be shut down.

Conversely, you may sometimes need to force a broker failover to occur manually. (This might be necessary, for instance, if a failover broker were to itself fail before completing the takeover process.) In such cases, you can initiate a failover manually from the command line: first shut down the broker to be taken over with the -nofailover option, as shown above, then issue the command

   imqcmd takeover bkr  -n brokerID

where brokerID is the broker identifier of the broker to be taken over. If the specified broker appears to be running, the Command utility will display a confirmation message:

   The broker associated with brokerID last accessed the database # seconds ago. 
   Do you want to take over for this broker?

You can suppress this message, and force the takeover to occur unconditionally, by using the -f option to the imqcmd takeover bkr command:

   imqcmd takeover bkr  -f  -n brokerID

The imqcmd takeover bkr subcommand is intended only for use in failed-takeover situations. You should use it only as a last resort, and not as a general way of forcibly taking over a running broker.

Converting a Standalone Data Store to a Shared Data Store

When converting to high-availability operation using an HADB dababse, you can use the Message Queue Database Manager utility (imqdbmgr) subcommand

   imqdbmgr upgrade hastore

to convert an existing standalone HADB database to a shared HADB database. You can use this command in the following cases:

• Migrating from a Message Queue 4.0 or 4.1 standalone HADB database to a Message Queue 4.2 shared HADB database. In this case, the broker, upon startup, will automatically upgrade the database schema to Message Queue 4.2. You can then run the imqdbmgr upgrade hastore command to convert the data store to shared use.

• Moving from a standalone Message Queue 4.21 HADB database to a shared HADB database. In this case, you just need to run the imqdbmgr upgrade hastore command to convert the data store to shared use.

Because this command only supports conversion of HADB stores, it cannot be used to convert file-based stores or other JDBC-based stores to a shared HADB store. If you were previously running a 3.x version of Message Queue, you must create an HADB store and then manually migrate your data to that store in order to use the high availability feature.

Backing up a Shared Data Store

For durability and reliability, it is a good idea to back up a high-availability cluster’s shared data store periodically to backup files. This creates a snapshot of the data store that you can then use to restore the data in case of catastrophic failure. The command for backing up the data store is

   imqdbmgr backup  -dir backupDir

where backupDir is the path to the directory in which to place the backup files. To restore the data store from these files, use the command

   imqdbmgr restore  -restore backupDir