Network Deployment (Distributed operating systems), v8.0 > Establishing high availability

Create a policy for a high availability group

Every high availability group has to have an associated policy. This policy determines which members of a high availability group to put in the active state. Before creating a new policy, you should review the following topics:

• High availability group policy modification guidelines
• High availability group policies

You should also know:

• The name of the core group to associate with the new policy.
• The name of the high availability group that you want this policy to control.
• The function, such as transaction log recovery or messaging engine, that is associated with this high availability group.
• The policy types, such as One of N or Static, that this function supports.
• The type of policy to create.
• The policy settings, such as failback, and preferred servers only, to configure for this policy.

The product includes default policies that are already associated with the high availability groups some of the product components use. If these default policies do not meet the requirements of your installation, IBM recommends that you create a new policy instead of changing one of the default policies. The creation of new policies provides you with the capability to tailor the policy settings to your installations requirements while giving you the option to revert back to the default policy.

To create a new policy:

Procedure

1. In the admin console, click...

       Servers > Core Groups > Core group settings > core_group_name > Policies > New.

2. Select the new policy you want in effect for a specific high availability group. If define a new policy, the policy options are:
   • All active policy: All of the group members are activated.
   • M of N policy: M group members are activated. The number that is represented by M is defined as part of the policy details.
   • No operation policy: No group members are activated.
   • One of N policy: Only one group member is activated.
   • Static policy: The active members of a group are statically configured.

   For messaging engines in service integration, only the Static, One of N, and No operation policies apply.

3. Click Next.

4. Specify a name for the policy in the Name field. The name must be unique within the scope of the core group. Make the name meaningful to other administrators.

5. Optional: Specify a Description of the policy in the description field. This description might include the name of the associated core group.

6. Specify a value for the Is alive timer field, if the default value is too long or too short a time period. This value determines how frequently the high availability manager checks the health of the high availability group members. The default value is 0 seconds.

   • If you specify -1 (minus 1), the Is alive timer is disabled.

   • If you specify 0 (zero), the value specified for the Is alive timer at the core group services level is used for high availability groups that are associated with this policy.

   • If you specify an integer between 1 and 2147483647, inclusive, this value is used for the high availability groups that are associated with this policy.

7. Make sure the Quorum field is not selected. You should not enable Quorum unless you are explicitly instructed to do so in the documentation for some other product.

8. Select the Failback field to have the high availability manager make the most preferred member the currently active member whenever this action is possible. This option is available only for M of N and One of N policies.

9. Select the Preferred servers only field if you want the high availability manager to only activate group members on servers that are contained in the Preferred servers list. This option is available only for M of N and One of N policies. If you select this option, configure a list of preferred servers. A description of how to set up this list is provided in a later optional step.

10. Specify the number of group members that you want active in the Number of active members field. This option is available only for an M of N policy.

11. Click Apply and then select Match criteria.

12. On the next panel, click New and then configure the match criterion for this policy.

    1. In the Name field, specify the name of one of the name-value pairs contained in the name of the high availability group that you want to associate with this policy.

    2. In the Value field, specify the value of the name-value pair you specified in the Name field.

    3. Optional: In the Description field, add a description of this match criterion . For example, you might specify First attribute to indicate that this name-value pair matches the first attribute contained in the group name.

    4. Click OK.
    5. Repeat these steps for each additional attribute you want to include as part of your match criterion.

    You should set the match criterion for a new policy to two or more of the name-value attributes that are contained in the name of the high availability group to ensure that this policy is used instead of one of the product default policies. Using this example, the following high availability group-to-policy association is established:

13. In the Additional Properties section, select the Static group servers field to configure the list of servers that you want activated. This option is available only for Static policies. Click Add to move core group servers into the list of Static group servers, and then Click OK after you complete the list.

14. Optional: Under Additional Properties, select Preferred servers and select the preferred servers for this policy. This option is available only if you selected the Preferred servers only field for M of N and One of N policies. If you do not set up this list, no group members are activated.

    Click Add to move core group servers into the list of preferred servers.

    Select specific servers in the list and click Move up and Move down to adjust the order of the servers within the list. Make sure that the most preferred server is at the beginning of the list and the least preferred server is at the end of the list.

    After you complete the preferred servers list, click OK.

    Use caution when selecting preferred servers. The product cannot detect if you select an inappropriate server as a preferred server. For example, if the policy affects a messaging engine or transaction service, only select preferred servers from the messaging engine cluster. Similarly, if the policy affects a transaction service, only select preferred servers from the transaction service cluster.

15. Click OK and then clickReview.

16. Select Synchronize changes with nodes, and then click Save.

Results

The new policy goes into affect after it is saved and synchronized. You do not have to stop and restart the affected application servers.

What to do next

We can change the Failback and Preferred servers only options for this policy without stopping and restarting the affected application servers.

We can create or update the list of preferred servers that for this policy without stopping and restarting the affected application servers.

Related

Core group policies
Core group policy settings
New core group policy definition
Preferred servers
Match criteria collection
Match criteria settings
Static group servers collection
High availability manager
Select the policy for a high availability group
Set up a high availability environment
Configure a core group policy for messaging engines

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