How the Package Manager Works, Package Types

IMPORTANT: During Step 1, while the nodes are using a strict majority quorum, node failures can cause the cluster to go down unexpectedly if the cluster has been using a quorum device before the configuration change. For example, suppose you change the Quorum Server polling interval while a two-node cluster is running. If a node fails during Step 1, the cluster will lose quorum and go down, because a strict majority of prior cluster members (two out of two in this case) is required. The duration of Step 1 is typically around a second, so the chance of a node failure occurring during that time is very small.

In order to keep the time interval as short as possible, make sure you are changing only the quorum configuration, and nothing else, when you apply the change.

If this slight risk of a node failure leading to cluster failure is unacceptable, halt the cluster before you make the quorum configuration change.

How the Package Manager Works

Packages are the means by which Serviceguard starts and halts configured applications. A package is a collection of services, disk volumes, IP addresses, and generic resources that are managed by Serviceguard to ensure they are available.

Each node in the cluster runs an instance of the package manager; the package manager residing on the cluster coordinator is known as the package coordinator.

The package coordinator does the following:

•Decides when and where to run, halt, or move packages. The package manager on all nodes does the following:

•Executes the control scripts that run and halt packages and their services.

•Reacts to changes in the status of monitored resources.

Package Types

Three different types of packages can run in the cluster; the most common is the failover package. There are also special-purpose packages that run on more than one node at a time, and so do not failover. They are typically used to manage resources of certain failover packages.

Non-failover Packages

There are two types of special-purpose packages that do not fail over and that can run on more than one node at the same time: the system multi-node package, which runs on all nodes in the cluster, and the multi-node package, which can be configured to run on all or some of the nodes in the cluster. System multi-node packages are reserved for use by HP-supplied applications, such as Veritas Cluster Volume Manager (CVM) and Cluster File System (CFS).

The rest of this section describes failover packages.

Failover Packages

A failover package starts up on an appropriate node (see node_name on (page 235)) when the cluster starts. A package failover takes place when the package coordinator initiates the start of a package on a new node. A package failover involves both halting the existing package (in the case of a service, network, or resource failure), and starting the new instance of the package.

Failover is shown in the following figure:

50 Understanding Serviceguard Software Components