HP-UC Cluster [Live Application Detach= LAD]

Live Application Detach= LAD

Halting a Node or the Cluster while Keeping Packages Running (Live Application Detach)

There may be circumstances in which you want to do maintenance that involves halting a node, or the entire cluster, without halting or failing over the affected packages. Such maintenance might consist of anything short of rebooting the node or nodes, but a likely case is networking changes that will disrupt the heartbeat.
New command options in Serviceguard A.11.20 (collectively known as Live Application Detach (LAD)) allow you to do this kind of maintenance while keeping the packages running. The packages are no longer monitored by Serviceguard, but the applications continue to run.
Packages in this state are called detached packages.
IMPORTANT:

• This capability applies only to modular failover packages and modular multi-node packages.
• When upgrading to future releases, you will be able to use LAD in conjunction with rolling upgrade, but you cannot use it when upgrading to A.11.20, because the capability is not available until all the nodes are running A.11.20.
• When you have done the necessary maintenance, you can restart the node or cluster, and normal monitoring will resume on the packages.

What You Can Do

You can do the following.

• Halt a node with the

# cmhaltnode -d 

without causing its running packages to halt or fail over.

• Until you restart the node

# cmrunnode

these packages are detached — not being monitored by Serviceguard.

• Halt the cluster

# cmhaltcl -d 

without causing its running packages to halt.

• Until you restart the cluster

# cmruncl 

these packages are detached — not being monitored by Serviceguard.

• Halt a detached package, including instances of detached multi-node packages.
• Restart normal package monitoring by restarting the node using cmrunnode or the cluster using cmruncl.

Rules and Restrictions

The following rules and restrictions apply.

• All the nodes in the cluster must be running A.11.20.
• All the configured cluster nodes must be reachable by an available network (not necessarily a network that is configured into the cluster).
• You must be root user (superuser) to halt or start a node or cluster with Live Application Detach, and to halt a detached package.
• Live Application Detach is not supported for SGeRAC clusters configured with SLVM or ASM.
• Live Application Detach is not supported for clusters using the Veritas Cluster Volume Manager (CVM) or Cluster File System (CFS).
• Live Application Detach is supported only for modular failover packages and modular multi-node packages.
• You cannot detach legacy packages,but you can halt them and then detach the modular packages.
• You cannot use Live Application Detach if system multi-node packages (such as SG-CFS-pkg) are configured in the cluster.
• You cannot detach a package that is in maintenance mode, and you cannot place a package into maintenance mode if any of its dependent packages are detached.
• → → You cannot make configuration changes to a cluster in which any packages are detached. cmapplyconf. ← ←
• You cannot halt detached packages while the cluster is down.
• If you have halted a node and detached its packages, you can log in as superuser on any other node still running in the cluster and halt any of the detached packages. But if you have halted the cluster, you must restart it, re-attaching the packages, before you can halt any of the packages
• If you are using LVM, all the cluster nodes must have Base LVM version B.11.31.0909 or later.
• HPVM shared volume groups are not supported with Live Application detach.
• cmeval does not support Live Application Detach.
• In preview mode (-t) cmrunnode and cmruncl can provide only a partial assessment of the effect of re-attaching packages.
• cmmodpkg -e -t is not supported for a detached package.
• You cannot run a package that has been detached.
• You cannot halt a package that is in a transitory state such as STARTING or HALTING.
• You cannot detach a package that has relocatable IP addresses on a subnet that is not configured into the cluster.
• You cannot detach packages when the HP-UX Clustered I/O Congestion Control feature is enabled.
• As of the date of this manual, you cannot detach ECMT-based packages.

Additional Points To Note

Keep the following points in mind.

• When packages are detached, they continue to run, but without high availability protection.
• cmviewcl reports the status and state of detached packages as detached. This is true even if a problem has occurred since the package was detached and some or all of the package components are not healthy or not running.
• Because Serviceguard assumes that a detached package has remained healthy, the package is considered to be UP for dependency purposes.
• As always, packages cannot start on a halted node or in a halted cluster.
• When you restart a node or cluster whose packages have been detached, the

packages are re-attached; that is, Serviceguard begins monitoring them again. At this point, Serviceguard checks the health of the packages that were detached and takes any necessary corrective action — for example, if a failover package has in fact failed while it was detached, Serviceguard will halt it and restart it on another eligible node.
CAUTION: Serviceguard does not check LVM volume groups and mount points when re-attaching packages.

• The detached state and status could appear to persist across a reboot.
• If you halt a package and disable it before running cmhaltcl -d to detach other packages running in the cluster, auto_run will be automatically re-enabled for this package when the cluster is started again, forcing the package to start.
• If an IP address is switched to the standby LAN because of a failure of on the primary LAN before a node is halted in detached mode, and if the failure is detected as an IP-only failure (meaning that the primary LAN was failed at the IP level only) then the IP address will remain on the standby LAN even after the node is restarted via cmrunnode. This will also happen if the IP address is switched to the standby LAN and NETWORK_AUTO_FAILBACK cluster parameter is set to FALSE.
• If the primary LAN recovers while the node is halted and you want the IP address to fail back to the primary LAN, run

# cmmodnet –e 

to re-enable the primary LAN interface and trigger the failback.

Halting a Node and Detaching its Packages

To halt a node and detach its packages, proceed as follows.

1. Halt any packages that do not qualify for Live Application Detach, such as legacy and system multi-node packages. # cmhaltpkg -n node1 legpak1 legpak2
2. Halt the node with the -d (detach) option: # cmhaltnode -d node1

To re-attach the packages, restart the node:

# cmrunnode -n node1

Halting a Detached Package

To halt a package that is detached on node1, proceed as follows.

1. Log in as superuser on another node that is still running in the cluster.
2. Halt the package

# cmhaltpkg node1 pkg1

Halting the Cluster and Detaching its Packages

1. Halt any packages that do not qualify for Live Application Detach, such as legacy and system multi-node packages.

# cmhaltpkg legpak1 legpak2 legpak3 smnp1

2. Halt the cluster with the -d (detach) option:

# cmhaltcl -d 

To re-attach the packages, restart cluster:

# cmrunnode node1

Example: Halting the Cluster for Maintenance on the Heartbeat Subnets

Suppose that you need to do networking maintenance that will disrupt all the cluster's heartbeat subnets, but it is essential that the packages continue to run while you do it. In this example we'll assume that packages pkg1 through pkg5 are unsupported for Live Application Detach, and pkg6 through pkgn are supported. Proceed as follows:

1. Halt all the unsupported packages

# cmhaltpkg pkg1 pkg2 pkg3 pkg4 pkg5

2. Halt the cluster, detaching the remaining packages

# cmhaltcl -d

3. Upgrade the heartbeat networks as needed.
4. Restart the cluster

# cmruncl

5. Start the remaining packages

# cmmodpkg -e pkg1 pkg2 pkg3 pkg4 pkg5

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