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Geo Clustering Guide

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Applies to SUSE Linux Enterprise High Availability Extension 12 SP5

6 Configuring Cluster Resources and Constraints #

6.1 Configuring Ticket Dependencies of Resources
6.2 Configuring a Resource Group for boothd
6.3 Adding an Ordering Constraint
6.4 Transferring the Resource Configuration to Other Cluster Sites

Apart from the resources and constraints that you need to define for your specific cluster setup, Geo clusters require additional resources and constraints as described below. You can either configure them with the crm shell (crmsh) as demonstrated in the examples below, or with the HA Web Konsole (Hawk2).

This chapter focuses on tasks specific to Geo clusters. For an introduction to your preferred cluster management tool and general instructions on how to configure resources and constraints with it, refer to one of the following chapters in the Administration Guide for SUSE Linux Enterprise High Availability Extension:

If you have set up your Geo cluster with the bootstrap scripts, the cluster resources needed for booth have been configured already (including a resource group for boothd). In this case, you can skip Section 6.2 and only need to execute the remaining steps below to complete the cluster resource configuration.

If you are setting up your Geo cluster manually, you need to execute all of the following steps:

Important: No CIB Synchronization Across Sites

The CIB is not automatically synchronized across cluster sites of a Geo cluster. All resources that must be highly available across the Geo cluster need to be configured for each site accordingly or need to be transferred to the other site or sites.

To simplify transfer, any resources with site-specific parameters can be configured in such a way that the parameters' values depend on the name of the cluster site where the resource is running (see also Chapter 3, Requirements, Other Requirements and Recommendations).

After you have configured the resources on one site, you can tag the resources that are needed on all cluster sites, export them from the current CIB, and import them into the CIB of another cluster site. For details, see Section 6.4, “Transferring the Resource Configuration to Other Cluster Sites”.

6.1 Configuring Ticket Dependencies of Resources #

For Geo clusters, you can specify which resources depend on a certain ticket. Together with this special type of constraint, you can set a loss-policy that defines what should happen to the respective resources if the ticket is revoked. The attribute loss-policy can have the following values:

fence: Fence the nodes that are running the relevant resources.
stop: Stop the relevant resources.
freeze: Do nothing to the relevant resources.
demote: Demote relevant resources that are running in master mode to slave mode.

Procedure 6.1: Configuring Ticket Dependencies of Resources with crmsh #

On one of the nodes of cluster amsterdam, start a shell and log in as root or equivalent.
Enter crm configure to switch to the interactive crm shell.
Configure constraints that define which resources depend on a certain ticket. For example, to make a primitive resource rsc1 depend on ticketA:
```
crm(live)configure# rsc_ticket rsc1-req-ticketA ticketA: \
  rsc1 loss-policy="fence"
```
In case ticketA is revoked, the node running the resource should be fenced.
If you want other resources to depend on further tickets, create as many constraints as necessary with rsc_ticket.
Review your changes with show.
If everything is correct, submit your changes with commit and leave the crm live configuration with exit.
The configuration is saved to the CIB.

6.2 Configuring a Resource Group for `boothd` #

If you have set up your Geo cluster with the ha-cluster-init bootstrap scripts, you can skip the following procedure as the resources and the resource group for boothd have already been configured in this case.

Each site needs to run one instance of boothd that communicates with the other booth daemons. The daemon can be started on any node, therefore it should be configured as primitive resource. To make the boothd resource stay on the same node, if possible, add resource stickiness to the configuration. As each daemon needs a persistent IP address, configure another primitive with a virtual IP address. Group both primitives:

On one of the nodes of cluster amsterdam, start a shell and log in as root or equivalent.
Enter crm configure to switch to the interactive crm shell.

Enter the following to create both primitive resources and to add them to one group, g-booth:

crm(live)configure# primitive ip-booth ocf:heartbeat:IPaddr2 \
  params iflabel="ha" nic="eth1" cidr_netmask="24"
  params rule #cluster-name eq amsterdam ip="192.168.201.100" \
  params rule #cluster-name eq berlin ip="192.168.202.100"
crm(live)configure# primitive booth-site ocf:pacemaker:booth-site \
  meta resource-stickiness="INFINITY" \
  params config="nfs" op monitor interval="10s"
crm(live)configure# group g-booth ip-booth booth-site

With this configuration, each booth daemon will be available at its individual IP address, independent of the node the daemon is running on.

Review your changes with show.
If everything is correct, submit your changes with commit and leave the crm live configuration with exit.
The configuration is saved to the CIB.

6.3 Adding an Ordering Constraint #

If a ticket has been granted to a site but all nodes of that site should fail to host the boothd resource group for any reason, a “split-brain” situation among the geographically dispersed sites may occur. In that case, no boothd instance would be available to safely manage failover of the ticket to another site. To avoid a potential concurrency violation of the ticket (the ticket is granted to multiple sites simultaneously), add an ordering constraint:

On one of the nodes of cluster amsterdam, start a shell and log in as root or equivalent.
Enter crm configure to switch to the interactive crm shell.
Create an ordering constraint, for example:
```
crm(live)configure# order o-booth-before-rsc1 inf: g-booth rsc1
```
It defines that rsc1 (which depends on ticketA) can only be started after the g-booth resource group.
For any other resources that depend on a certain ticket, define further ordering constraints.
Review your changes with show.
If everything is correct, submit your changes with commit and leave the crm live configuration with exit.
The configuration is saved to the CIB.

6.4 Transferring the Resource Configuration to Other Cluster Sites #

After having completed or changed your resource configuration for one cluster site, transfer it to the other sites of your Geo cluster.

To simplify the transfer, you can tag any resources that are needed on all cluster sites, export them from the current CIB, and import them into the CIB of another cluster site. Tagging does not create any colocation or ordering relationship between the resources.

Procedure 6.2, “Tagging and Exporting a Resource Configuration” and Procedure 6.3, “Importing a Tagged Resource Configuration” give an example of how to do so. They are based on the following prerequisites:

Prerequisites #

You have a Geo cluster with two sites: cluster amsterdam and cluster berlin.
The cluster names for each site are defined in the respective /etc/corosync/corosync.conf files:
```
totem {
     [...]
     cluster_name: amsterdam
     }
```
This can either be done manually (by editing /etc/corosync/corosync.conf) or with the YaST cluster module (by switching to the Communication Channels category and defining a Cluster Name). Afterward, stop and start the pacemaker service for the changes to take effect:
```
root # systemctl stop pacemaker
root # systemctl start pacemaker
```
The necessary resources for booth and for all services that should be highly available across your Geo cluster have been configured in the CIB on site amsterdam. They will be imported to the CIB on site berlin.

Procedure 6.2: Tagging and Exporting a Resource Configuration #

Log in to one of the nodes of cluster amsterdam.
Start the cluster with:
```
root # systemctl start pacemaker
```
Enter crm configure to switch to the interactive crm shell.
Review the current CIB configuration:
```
crm(live)configure# show
```

Mark the resources and constraints that are needed across the Geo cluster with the tag geo_resources:

crm(live)configure# tag geo_resources: \
  LIST_OF_RESOURCES_and_CONSTRAINTS_FOR_REQUIRED_SERVICES 1\
  rsc1-req-ticketA ip-booth booth-site g-booth o-booth-before-rsc1 2

1	Any resources and constraints of your specific setup that you need on all sites of the Geo cluster (for example, resources for DRBD as described at https://documentation.suse.com/sbp/all/html/SBP-DRBD/index.html).
2	Resources and constraints for boothd (primitives, booth resource group, ticket dependency, additional ordering constraint), see Section 6.1 to Section 6.3.

Review your changes with show.
If the configuration is according to your wishes, submit your changes with submit and leave the crm live shell with exit.
Export the tagged resources and constraints to a file named exported.cib:
```
root # crm configure show tag:geo_resources geo_resources > exported.cib
```
The command crm configure show tag:TAGNAME shows all resources that belong to the tag TAGNAME.

Procedure 6.3: Importing a Tagged Resource Configuration #

To import the saved configuration file into the CIB of the second cluster site, proceed as follows:

Log in to one of the nodes of cluster berlin.
Start the cluster with:
```
root # systemctl start pacemaker
```
Copy the file exported.cib from cluster amsterdam to this node.
Import the tagged resources and constraints from the file exported.cib into the CIB of cluster berlin:
```
root # crm configure load update PATH_TO_FILE/exported.cib
```
When using the update parameter for the crm configure load command, crmsh tries to integrate the contents of the file into the current CIB configuration (instead of replacing the current CIB with the file contents).
View the updated CIB configuration with the following command:
```
root # crm configure show
```
The imported resources and constraints will appear in the CIB.

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