HP Serviceguard manual Implications for Application Deployment

monitored_subnet_access unconfigured for a monitored subnet is equivalent to FULL.)

(For legacy packages, see “Configuring Cross-Subnet Failover” (page 309).)

•You should not use the wildcard (*) for node_name (page 235) in the package configuration file, as this could allow the package to fail over across subnets when a node on the same subnet is eligible. Failing over across subnets can take longer than failing over on the same subnet. List the nodes in order of preference instead of using the wildcard.

•Each subnet interface (NIC) used by the package must have a standby interface on the local bridged net.

The standby interface can be shared between subnets.

•Deploying applications in this environment requires careful consideration; see “Implications for Application Deployment” (page 155).

•If a monitored_subnet (page 241) is configured for PARTIAL

monitored_subnet_access in a package’s configuration file, it must be configured on at least one of the nodes on the node_name list for that package.

Conversely, if all of the subnets that are being monitored for this package are configured for PARTIAL access, each node on the node_name list must have at least one of these subnets configured.

◦As in other cluster configurations, a package will not start on a node unless the subnets configured on that node, and specified in the package configuration file as monitored subnets, are up.

Implications for Application Deployment

Because the relocatable IP address will change when a package fails over to a node on another subnet, you need to make sure of the following:

•The hostname used by the package is correctly remapped to the new relocatable IP address.

•The application that the package runs must be configured so that the clients can reconnect to the package’s new relocatable IP address.

In the worst case (when the server where the application was running is down), the client may continue to retry the old IP address until TCP’s tcp_timeout is reached (typically about ten minutes), at which point it will detect the failure and reset the connection.

For more information, see the white paper Technical Considerations for Creating a Serviceguard Cluster that Spans Multiple IP Subnets, at http://www.hp.com/go/hpux-serviceguard-docs.

Configuring a Package to Fail Over across Subnets: Example

To configure a package to fail over across subnets, you need to make some additional edits to the package configuration file.

NOTE: This section provides an example for a modular package; for legacy packages, see “Configuring Cross-Subnet Failover” (page 309).

Suppose that you want to configure a package, pkg1, so that it can fail over among all the nodes in a cluster comprising NodeA, NodeB, NodeC, and NodeD.

NodeA and NodeB use subnet 15.244.65.0, which is not used by NodeC and NodeD; and NodeC and NodeD use subnet 15.244.56.0, which is not used by NodeA and NodeB. (See “Obtaining Cross-Subnet Information” (page 190) for sample cmquerycl output).

Package Configuration Planning 155