Configure Pacemaker and STONITH

In this article, we will explore how to configure Pacemaker and STONITH (Shoot The Other Node In The Head) for high availability in an Azure environment for SAP workloads. Pacemaker is an advanced, scalable, and open-source cluster resource manager, while STONITH is a technique used to ensure the isolation of failed nodes in a cluster.

Before we dive into the configuration, let’s understand the importance of using Pacemaker and STONITH in an Azure environment for SAP workloads. SAP workloads are typically critical and require high availability to ensure continuous business operations. Pacemaker helps ensure that the workloads are highly available by managing and monitoring cluster resources, while STONITH ensures that a faulty node is safely fenced off from the cluster, preventing any potential data corruption.

Now, let’s proceed with the step-by-step configuration.

Step 1: Create Azure Virtual Machines

First, we need to create multiple Azure Virtual Machines (VMs) that will form our cluster. These VMs should be located in the same Azure Virtual Network (VNet) and should have the necessary SAP software installed. Ensure that the VMs are running the supported operating system for SAP workloads.

Step 2: Install Required Software

On each VM, install the required software: Pacemaker and STONITH. These packages can be installed using the package manager of your operating system. For example, on a Linux-based distribution such as SUSE Linux Enterprise Server (SLES), you can use the following commands:

sudo zypper install pacemaker
sudo zypper install stonith

Step 3: Configure Pacemaker

Once the software is installed, we need to configure Pacemaker. The configuration is typically done through a configuration file, which can be located at /etc/corosync/corosync.conf on SLES.

Open the configuration file using a text editor and configure the following parameters:

• Set the cluster name:

totem {
cluster_name:
}


• Specify the cluster interfaces:

nodelist {
node {
ring0_addr:
name:
nodeid: 1
}
node {
ring0_addr:
name:
nodeid: 2
}
}


• Configure the quorum policy:

quorum {
provider: corosync_votequorum
expected_votes: 2
two_node: 1
}

• Define the resources to be managed by Pacemaker. For example, you can define a resource for the SAP application:

primitive sap_app ocf:sap: \
op stop timeout="180" interval="0" \
op start timeout="180" interval="0" \
op monitor timeout="30" interval="60"


These are just examples, and you should refer to the specific documentation for your SAP resource agent and configuration details.

Step 4: Configure STONITH

Now, let’s configure STONITH to ensure safe node isolation. There are various STONITH mechanisms available, such as power fencing, IPMI, or virtual power fencing. In an Azure environment, we can leverage Azure PowerShell and Azure CLI commands to achieve fencing.

For example, you can use Azure PowerShell to configure a power fencing STONITH mechanism:

Add-AzVmssDiskEncryptionSet -ResourceId -DiskEncryptionSetId


Again, please refer to the Azure documentation for the specific STONITH mechanism you want to implement.

Step 5: Start the Cluster

Once the Pacemaker and STONITH configurations are complete, we can start the cluster by starting the corosync service:

sudo systemctl start corosync

And then, start the pacemaker service:

sudo systemctl start pacemaker

Step 6: Test High Availability

To ensure high availability, test the failover scenario by simulating a failure on one of the nodes. You can do this by powering off one of the VMs or by intentionally stopping the pacemaker or SAP application on one of the nodes.

Observe if the resources are successfully transferred to the other available node. Monitor the cluster status using commands such as crm_mon or Pacemaker’s web-based GUI.

Conclusion

By configuring Pacemaker and STONITH in an Azure environment for SAP workloads, you can ensure high availability and fault tolerance. Pacemaker manages and monitors cluster resources, while STONITH isolates failed nodes to prevent data corruption. Follow the steps outlined in this article to properly configure Pacemaker and STONITH, and test the high availability of your SAP workloads in an Azure environment.

Please note that this article provides a high-level overview of the configuration process. For detailed configuration specifics, consult the Microsoft Azure documentation and the specific documentation for your SAP resource agent.