Pacemaker and STONITH (Shoot The Other Node In The Head) are two significant configurations for ensuring high availability and avoiding split-brain conditions in Azure for SAP workloads. Implementing these configurations demands an understanding of both Linux-based Pacemaker technology and Azure’s specific configurations for SAP applications.
What are Pacemaker and STONITH?
Pacemaker is an advanced, scalable, and robust High Availability (HA) cluster resource manager for Linux-based systems. It groups multiple servers together and manages the distribution of workloads among them to ensure high availability.
STONITH is a critical component in the high-availability cluster data strategy, ensuring data integrity by maintaining a single active version of your data. It reduces the risk of ‘split-brain’ scenarios, where two or more clusters believe they have exclusive control over the shared resources, leading to data loss or corruption.
These technologies, when used together, provide a robust strategy for managing high-availability clusters in SAP Workloads on Azure.
Configuring Pacemaker and STONITH on Azure
Setting up Pacemaker on Azure for SAP involves installation and configuration. Linux distributions include support for Pacemaker, but the actual configuration will depend on your specific SAP application and setup.
Navigate to the Linux terminal and run the following command to install Pacemaker:
sudo yum install pacemaker pcs fence-agents-all
After installing Pacemaker, setup requires authentication for cluster nodes, creating the cluster, and then adding nodes. Below are the commands to use:
sudo pcs cluster auth node1 node2
sudo pcs cluster setup –name clustername node1 node2
sudo pcs cluster start –all
Remember to replace ‘node1’ and ‘node2’ with the names of the nodes you want to include in your cluster and ‘clustername’ with the chosen name for your cluster.
STONITH implementation on Azure uses a module called `fence_azure_arm`, and its setup involves configuring the cluster properties and the STONITH devices.
To configure the cluster properties, use this command:
sudo pcs property set stonith-enabled=true
To add a STONITH or fencing device, use the following command:
sudo pcs stonith create fence_vm1 fence_azure_arm pcmk_host_map=”vm1:vm1-id” subscriptionId=”sub-id” resourceGroup=”rg” tenantId=”tenant-id” login=”client-id” passwd=”client-secret” power_wait=300 verbose=yes
“vm1” should be replaced with the name of the STONITH node, and the corresponding IDs and Azure information should also be replaced accordingly.
Verifying Proper Configuration
After you have configured Pacemaker and STONITH, it is vital to verify your configuration to ensure everything is set correctly. To verify the status of your nodes, check if the nodes are in standby mode, and confirm that the properties are appropriately set, use the following commands:
sudo pcs status nodes
sudo pcs status standby
sudo pcs property
The output should give you pertinent information about your nodes and cluster configuration.
Configuring Pacemaker and STONITH for SAP workloads on Azure can improve your system’s high availability and prevent data corruption due to split-brain scenarios. As every setup is unique, you must understand your specific SAP application and Azure configuration to make the right choices when setting up and managing these useful tools.
Practice Test
True or False: Pacemaker is a free automated high availability resource manager that can be used with Azure for SAP workloads.
- True
- False
Answer: True
Explanation: Pacemaker is a key component of the Azure high availability stack for SAP, and it can be used to monitor and manage SAP applications to ensure that they stay up and running.
What is the primary function of STONITH in the context of high availability configurations?
- A) It is used for load balancing.
- B) It is used for session replication.
- C) It is used as a fencing mechanism to isolate nodes suspected to be faulty.
- D) It is used for disaster recovery.
Answer: C
Explanation: STONITH, which stands for ‘Shoot The Other Node In The Head,’ is a fencing mechanism in high availability configurations, used to isolate and power down nodes suspected to be faulty.
Which of the following tools can be used for configuring STONITH in Azure for SAP workloads?
- A) Azure CLI
- B) Azure DevOps
- C) Azure Cosmos DB
- D) Azure Functions
Answer: A
Explanation: The Azure CLI (Command Line Interface) is a powerful toolset that can be used to manage Azure resources including configuring STONITH.
True or False: Azure does not provide any built-in support for SAP-specific high availability configurations and requires manual setup of tools like Pacemaker.
- True
- False
Answer: False
Explanation: Azure provides built-in support for various SAP high availability configurations and provides a standard set of scripts to deploy Pacemaker clusters for SAP.
What does STONITH stand for?
- A) Shoot The Other Node In The Heart
- B) Shoot The Other Node In The Head
- C) Shoot This Other Node In Time
- D) Shoot The Other Node In Hell
Answer: B
Explanation: STONITH is an acronym for ‘Shoot The Other Node In The Head’, illustrating the extreme measures taken to isolate potentially faulty nodes in high availability configurations.
True or False: Configuring both Pacemaker and STONITH correctly is essential to minimize system downtime for SAP Workloads on Azure.
- True
- False
Answer: True
Explanation: Both Pacemaker and STONITH are essential to handle and prevent system failures on Azure for SAP Workloads.
Multiple select: which of the following can function as an alternative to STONITH fencing mechanism?
- A) Azure Site Recovery
- B) Leased fencing
- C) Microsoft Power Automate
- D) DLM fencing
Answer: B & D
Explanation: In cloud platforms like Azure, hardware-based STONITH mechanisms are not possible, thus an alternative fencing method, typically DLM (Distributed Lock Manager) fencing or Leased fencing is used.
Pacemaker is a type of:
- A) Fencing mechanism
- B) High availability resource manager
- C) Load balancer
- D) Disaster recovery tool
Answer: B
Explanation: Pacemaker acts as a high availability resource manager, keeping track of multiple resources in a cluster and managing their state.
True or False: In Pacemaker configuration, the preferred mode of operation is active/active.
- True
- False
Answer: False
Explanation: In Pacemaker configuration for SAP systems, the preferred mode is active/passive to ensure reliable failover if a fault occurs.
True or False: Both Pacemaker and STONITH configurations are mandatory in the Azure environment for SAP workloads.
- True
- False
Answer: False
Explanation: Although using Pacemaker and STONITH could enhance the high availability of SAP workloads, they are not necessarily mandatory especially considering Azure’s inherent redundancy capabilities.
Interview Questions
What is Pacemaker in the context of SAP workloads on Azure?
Pacemaker is an open-source high availability resource manager software. It offers the functionalities for creating, managing and monitoring redundant resources on a cluster of servers to maintain availability of services in case of failures.
Can you explain the concept of STONITH in the context of Pacemaker and Azure for SAP workloads?
STONITH, which stands for ‘Shoot-The-Other-Node-In-The-Head’, is a fencing technique in cluster environments used to maintain the integrity and consistency of shared data. If a node in a cluster is non-responsive, STONITH ensures that the node is isolated to prevent it from modifying shared data.
How does Pacemaker ensure high availability of SAP workloads on Azure?
Pacemaker ensures high availability by detecting failures in the Azure infrastructure and initiating automatic failover to the secondary system. It manages virtual IP addresses, filesystem mounts, and SAP instances and services to ensure smooth and consistent operations.
Why is STONITH important in maintaining SAP workloads on Azure?
STONITH is a fundamental part of maintaining distributed consistency in a cluster environment. For SAP instances, it ensures the integrity of the data by isolating failed nodes, which could otherwise create a “split-brain” scenario, causing potential data corruption.
How can you implement STONITH in an Azure environment?
Azure implements STONITH through Azure fencing agent. This can be configured using the Pacemaker’s property stonith-enabled=true. The fencing agent uses Azure’s APIs to isolate or “power off” the problematic node from the cluster.
Can Pacemaker work without STONITH enabled?
Yes, it can work but it is not recommended for production deployments. Without STONITH, there is an increased risk of “split-brain” condition, which can lead to serious data inconsistency or corruption.
In the context of SAP complexities, tell me about the advantage of using the Pacemaker on a Linux environment above Azure.
Pacemaker offers automatic detection and recovery from machine, network and service-level failures for complex SAP environments. It removes single points of failure and integrates well with cloud environments like Azure, offering horizontal scalability.
Does Azure support the integration of Pacemaker resource agents for SAP applications?
Yes, Azure supports the integration of Pacemaker resource agents designed specifically for managing SAP applications. It helps in cluster resource management to maintain high availability.
How do you check the status of all nodes in a Pacemaker cluster on Azure?
You can check the status of all the nodes using the “crm_mon -1” command. It displays the current status of the entire cluster in an easily understandable format.
What would happen if a node in a Pacemaker cluster on Azure fails to communicate with the others?
If a node in a Pacemaker cluster fails to communicate, STONITH would come into play to isolate the node to maintain data integrity. Following that, Pacemaker will initiate a failover process to transfer the activities of the failed node to a functioning one.
What is the meaning of ‘A resource has failed’ on Pacemaker status?
‘A resource has failed’ indicates that a resource managed by Pacemaker has encountered an error. Pacemaker will try to recover the resource based on the configured failure policies, which might include restarting the resource, moving it to another node, or stopping all resources in the cluster.
How are Azure Virtual Machines used with STONITH fencing agents for SAP Workloads?
Azure Virtual Machines are used with the STONITH fencing agent for automatic recovery from failures and isolation of inconsistent nodes. The fencing agent communicates with the Azure APIs to de-allocate, stop or fencing the problematic Azure VMs.
How can you view the Pacemaker logs?
Pacemaker logs are by default sent to the system log, which can be viewed using the system log viewer. For a better understanding of errors or issues, you can also configure Pacemaker to provide more detailed logs.
Can Pacemaker clusters on Azure span across Azure regions?
Pacemaker clusters on Azure are generally limited to a single region to limit latency. However, Azure does provide options for inter-region connectivity, so it is technically possible to set up a Pacemaker cluster spanning multiple Azure regions.
What happens if the STONITH device fails in a Pacemaker environment on Azure?
If a STONITH device fails, it needs to be fixed immediately, or else the cluster may become at risk. As long as STONITH is configured and at least one STONITH resource is functional, then Pacemaker will keep all other resources stopped until the situation can be resolved manually.
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