High availability group policy selection process

Overview

Every high availability group has a unique group name that consists of a set of name-value pairs. Every policy definition contains an attribute called match criteria that is also a set of name-value pairs. To determine the policy for a high availability group, the group name is compared to the match criteria of all the associated core group polices. The policy with the strongest match to the group name is assigned to the high availability group

The high availability manager:

1. Finds the set of policies eligible to govern a high availability group.

   For a policy to be eligible, all name-value pairs in the match criteria of an eligible policy must be contained in the name of the high availability group.

2. Selects the policy that has the most name-value pair matches from the list of eligible policies, and uses that policy to govern the high availability group.

We can control the name-value pairs that make up a policy match criteria.

WAS ND v7.0 includes a couple of predefined policies.

 

Example 1

If the following conditions are satisfied, the policy "Clustered TM Policy" is selected for the transaction manager HA group:

• Cluster member MyServer1 is started.

• The transaction manager component code joins an HA manager to the high availability group named:

  GN_PS=testCell\testNode\MyServer1,IBM_hc=MyCluster,type=WAS_TRANSACTIONS

• MyServer1 is defined as a member of the DefaultCoreGroup core group for which the following policies are defined:

  Policy	Match criteria
  Clustered TM Policy	type=WAS_TRANSACTIONS
  Default SIBus Policy	type=WSAF_SIB

• The HA manager determines that Clustered TM Policy is the closest match because the match criteria...

  type=WAS_TRANSACTIONS

  ...is a proper subset of the HA group name.

 

Example 2

In this example, the administrator creates a new policy in the DefaultCoreGroup configuration called...

Administrator TM Policy

If the following conditions are satisfied, this policy is selected for the transaction manager HA group...

• Cluster member MyServer1 is started.

• The transaction manager component code joins a HA manager to the HA group named:

  GN_PS=testCell\testNode\MyServer1,IBM_hc=MyCluster,type=WAS_TRANSACTIONS

• MyServer1 is defined as a member of the DefaultCoreGroup core group, for which the following policies are defined:

  Clustered TM Policy	type=WAS_TRANSACTIONS
  Default SIBus Policy	type=WSAF_SIB
  Administrator TM Policy	IBM_hc=MyCluster,type=WAS_TRANSACTIONS

• The HA manager eliminates the Default SIBus Policy because the match criteria is not a proper subset of the HA group name. It determines that Clustered TM Policy and Administrator TM Policy are both eligible policies, because their match criteria are proper subsets of the HA group name.

  Because Administrator TM Policy has two matching pairs...

  • IBM_hc=MyCluster
  • type=WAS_TRANSACTIONS

  ...the HA manager associates Administrator TM Policy with the transaction manager HA group.

 

Ambiguous Matches

Do not configure identical match criteria for multiple policies in the same core group. Set identical match criteria causes an ambiguous match to the associated HA group. Because a HA group can only be associated with one policy, if the previously described matching mechanism does not result in a single policy match, the HA manager puts the HA group in error state, and does not make any of the group members active. Depending on the nature of the problem, the HA manager might write one of the following error messages to SystemOut.log:

HMGR0301W: No policy was located for the group named {0} HMGR0302W: Multiple policies match the group named {0}, Matching Policies are {1}

You can use the admin console to view the policies associated with a HA group and the current state of members of that group.

 

Related

High availability groups
High availability group policies