Use ARM in an IBM MQ network

We can set up your queue manager so that the channel initiators and associated listeners are started automatically when the queue manager is restarted.

• Start your listeners automatically by adding the appropriate START LISTENER command to the CSQINPX data set.
• Start your channel initiator automatically by adding the appropriate START CHINIT command to the CSQINP2 data set.

For restarting a queue manager with TCP/IP or LU6.2, see

• Restarting on a different z/OS image with TCP/IP
• Restarting on a different z/OS image with LU 6.2

See Task 13: Customize the initialization input data sets for information about the CSQINP2 and CSQINPX data sets.

Restarting on a different z/OS image with TCP/IP

If we are using TCP/IP as your communication protocol, and we are using virtual IP addresses, you can configure these to recover on other z/OS images, allowing channels connecting to that queue manager to reconnect without any changes. Otherwise, you can reallocate a TCP/IP address after moving a queue manager to a different z/OS image only if we are using clusters or if we are connecting to a queue sharing group using a WLM dynamic Domain Name System (DNS) logical group name.

• When using clustering
• When connecting to a queue sharing group

When using clustering

z/OS ARM responds to a system failure by restarting the queue manager on a different z/OS image in the same sysplex; this system has a different TCP/IP address to the original z/OS image. The following explains how we can use IBM MQ clusters to reassign a queue manager's TCP/IP address after it has been moved by ARM restart to a different z/OS image.

When a client queue manager detects the queue manager failure (as a channel failure), it responds by reallocating suitable messages on its cluster transmission queue to a different server queue manager that hosts a different instance of the target cluster queue. However, it cannot reallocate messages that are bound to the original server by affinity constraints, or messages that are in doubt because the server queue manager failed during end-of-batch processing. To process these messages, do the following:

1. Allocate a different cluster-receiver channel name and a different TCP/IP port to each z/OS queue manager. Each queue manager needs a different port so that two systems can share a single TCP/IP stack on a z/OS image. One of these is the queue manager originally running on that z/OS image, and the other is the queue manager that ARM will restart on that z/OS image following a system failure. Configure each port on each z/OS image, so that ARM can restart any queue manager on any z/OS image.
2. Create a different channel initiator command input file (CSQINPX) for each queue manager and z/OS image combination, to be referenced during channel initiator startup.

   Each CSQINPX file must include a START LISTENER PORT(port) command specific to that queue manager, and an ALTER CHANNEL command for a cluster-receiver channel specific to that queue manager and z/OS image combination. The ALTER CHANNEL command needs to set the connection name to the TCP/IP name of the z/OS image on which it is restarted. It must include the port number specific to the restarted queue manager as part of the connection name.

   The start-up JCL of each queue manager can have a fixed data set name for this CSQINPX file, and each z/OS image must have a different version of each CSQINPX file on a non-shared DASD volume.

If an ARM restart occurs, IBM MQ advertises the changed channel definition to the cluster repository, which in turn publishes it to all the client queue managers that have expressed an interest in the server queue manager.

The client queue manager treats the server queue manager failure as a channel failure, and tries to restart the failed channel. When the client queue manager learns the new server connection-name, the channel restart reconnects the client queue manager to the restarted server queue manager. The client queue manager can then resynchronize its messages, resolve any in-doubt messages on the client queue manager's transmission queue, and normal processing can continue.

When connecting to a queue sharing group

When connecting to a queue sharing group through a TCP/IP dynamic Domain Name System (DNS) logical group name, the connection name in your channel definition specifies the logical group name of our queue sharing group, not the host name or IP address of a physical machine. When this channel starts, it connects to the dynamic DNS and is then connected to one of the queue managers in the queue sharing group. This process is explained in Set up communication for IBM MQ for z/OS using queue sharing groups.

In the unlikely event of an image failure, one of the following occurs:

• The queue managers on the failing image de-register from the dynamic DNS running on your sysplex. The channel responds to the connection failure by entering RETRYING state and then connects to the dynamic DNS running on the sysplex. The dynamic DNS allocates the inbound request to one of the remaining members of the queue sharing group that is still running on the remaining images.
• If no other queue manager in the queue sharing group is active and ARM restarts the queue manager and channel initiator on a different image, the group listener registers with dynamic DNS from this new image. This means that the logical group name (from the connection name field of the channel) connects to the dynamic DNS and is then connected to the same queue manager, now running on a different image. No change was required to the channel definition.

For this type of recovery to occur, the following points must be noted:

• On z/OS, the dynamic DNS runs on one of the z/OS images in the sysplex. If this image were to fail, the dynamic DNS needs to be configured so that there is a secondary name server active in the sysplex, acting as an alternative to the primary name server. Information about primary and secondary dynamic DNS servers can be found in the OS/390 SecureWay CS IP Configuration manual.
• The TCP/IP group listener might have been started on a particular IP address that might not be available on this z/OS image. If so, the listener might need to be started on a different IP address on the new image. If we are using virtual IP addresses, we can configure these to recover on other z/OS images so that no change to the START LISTENER command is required.

Restarting on a different z/OS image with LU 6.2

• Define each queue manager within the sysplex with a unique subsystem name.
• Define each channel initiator within the sysplex with a unique LUNAME. This is specified in both the queue manager attributes and in the START LISTENER command. Note: The LUNAME names an entry in the APPC side table, which in turn maps this to the actual LUNAME.
• Set up a shared APPC side table, which is referenced by each z/OS image within the sysplex. This should contain an entry for each channel initiator's LUNAME. See the MVS Planning: APPC/MVS Management manual for information about this.
• Set up an APPCPM xx member of SYS1.PARMLIB for each channel initiator within the sysplex to contain an LUADD to activate the APPC side table entry for that channel initiator. These members should be shared by each z/OS image. The appropriate SYS1.PARMLIB member is activated by a z/OS command SET APPC= xx, which is issued automatically during ARM restart of the queue manager (and its channel initiator) on a different z/OS image, as described in the following text.
• Use the LU62ARM queue manager attribute to specify the xx suffix of this SYS1.PARMLIB member for each channel initiator. This causes the channel initiator to issue the required z/OS command SET APPC= xx to activate its LUNAME.

Define the ARM policy so that it restarts the channel initiator only if it fails while its z/OS image stays up; the user ID associated with the XCFAS address space must be authorized to issue the IBM MQ command START CHINIT. Do not restart the channel initiator automatically if its z/OS image also fails, instead use commands in the CSQINP2 and CSQINPX data sets to start the channel initiator and listeners.