Deploy a Pacemaker cluster for SQL Server on Linux

Applies to: SQL Server - Linux

This tutorial documents the tasks required to deploy a Linux Pacemaker cluster for a SQL Server Always On availability group (AG) or failover cluster instance (FCI). Unlike the tightly coupled Windows Server/ SQL Server stack, Pacemaker cluster creation as well as availability group (AG) configuration on Linux can be done before or after installation of SQL Server. The integration and configuration of resources for the Pacemaker portion of an AG or FCI deployment is done after the cluster is configured.

Prerequisite

Install SQL Server 2017.

Install the high availability add-on

Use the following syntax to install the packages that make up the high availability (HA) add-on for each distribution of Linux.

Red Hat Enterprise Linux (RHEL)

1. Register the server using the following syntax. You are prompted for a valid username and password.

   sudo subscription-manager register
   

2. List the available pools for registration.

   sudo subscription-manager list --available
   

3. Run the following command to associate RHEL high availability with the subscription

   sudo subscription-manager attach --pool=<PoolID>
   

   where PoolId is the pool ID for the high availability subscription from the previous step.

4. Enable the repository to be able to use the high availability add-on.

   sudo subscription-manager repos --enable=rhel-ha-for-rhel-7-server-rpms
   

5. Install Pacemaker.

   sudo yum install pacemaker pcs fence-agents-all resource-agents
   

Ubuntu

sudo apt-get install pacemaker pcs fence-agents resource-agents

SUSE Linux Enterprise Server (SLES)

Install the High Availability pattern in YaST or do it as part of the main installation of the server. The installation can be done with an ISO/DVD as a source or by getting it online.

Prepare the nodes for Pacemaker (RHEL and Ubuntu only)

Pacemaker itself uses a user created on the distribution named hacluster. The user gets created when the HA add-on is installed on RHEL and Ubuntu.

1. On each server that will serve as a node of the Pacemaker cluster, create the password for a user to be used by the cluster. The name used in the examples is hacluster, but any name can be used. The name and password must be the same on all nodes participating in the Pacemaker cluster.

   sudo passwd hacluster
   

2. On each node that will be part of the Pacemaker cluster, enable and start the pcsd service with the following commands (RHEL and Ubuntu):

   sudo systemctl enable pcsd
   sudo systemctl start pcsd
   

   Then execute

   sudo systemctl status pcsd
   

   to ensure that pcsd is started.

3. Enable the Pacemaker service on each possible node of the Pacemaker cluster.

   sudo systemctl start pacemaker
   

   On Ubuntu, you see an error:

   pacemaker Default-Start contains no runlevels, aborting.

   This error is a known issue. Despite the error, enabling the Pacemaker service is successful, and this bug will be fixed at some point in the future.

4. Next, create and start the Pacemaker cluster. There is one difference between RHEL and Ubuntu at this step. While on both distributions, installing pcs configures a default configuration file for the Pacemaker cluster, on RHEL, executing this command destroys any existing configuration and creates a new cluster.

Create the Pacemaker cluster

This section documents how to create and configure the cluster for each distribution of Linux.

RHEL

1. Authorize the nodes

   sudo pcs cluster auth <Node1 Node2 ... NodeN> -u hacluster
   

   where NodeX is the name of the node.

2. Create the cluster

   sudo pcs cluster setup --name <PMClusterName Nodelist> --start --all --enable
   

   where PMClusterName is the name assigned to the Pacemaker cluster and Nodelist is the list of names of the nodes separated by a space.

Ubuntu

Configuring Ubuntu is similar to RHEL. However, there is one major difference: installing the Pacemaker packages creates a base configuration for the cluster, and enables and starts pcsd. If you try to configure the Pacemaker cluster by following the RHEL instructions exactly, you get an error. To fix this problem, perform the following steps:

1. Remove the default Pacemaker configuration from each node.

   sudo pcs cluster destroy
   

2. Follow the steps in the RHEL section for creating the Pacemaker cluster.

SLES

The process for creating a Pacemaker cluster is completely different on SLES than it is on RHEL and Ubuntu. The following steps document how to create a cluster with SLES.

1. Start the cluster configuration process by running

   sudo ha-cluster-init
   

   on one of the nodes. You may be prompted that NTP is not configured and that no watchdog device is found. That is fine for getting things up and running. Watchdog is related to STONITH if you use SLES's built-in fencing that is storage-based. NTP and watchdog can be configured later.

2. You are prompted to configure Corosync. You are asked for the network address to bind to, as well as the multicast address and port. The network address is the subnet that you are using; for example, 192.191.190.0. You can accept the defaults at every prompt, or change if necessary.

3. Next, you are asked if you want to configure SBD, which is the disk-based fencing. This configuration can be done later if desired. If SBD is not configured, unlike on RHEL and Ubuntu, stonith-enabled will by default be set to false.

4. Finally, you are asked if you want to configure an IP address for administration. This IP address is optional, but functions similar to the IP address for a Windows Server failover cluster (WSFC) in the sense that it creates an IP address in the cluster to be used for connecting to it via HA Web Konsole (HAWK). This configuration, too, is optional.

5. Ensure that the cluster is up and running by issuing

   sudo crm status
   

6. Change the hacluster password with

   sudo passwd hacluster
   

7. If you configured an IP address for administration, you can test it in a browser, which also tests the password change for hacluster.

8. On another SLES server that will be a node of the cluster, run

   sudo ha-cluster-join
   

9. When prompted, enter the name or IP address of the server that was configured as the first node of the cluster in the previous steps. The server is added as a node to the existing cluster.

10. Verify the node was added by issuing

sudo crm status

11. Change the hacluster password with

sudo passwd hacluster

12. Repeat Steps 8-11 for all other servers to be added to the cluster.

Install the SQL Server HA and SQL Server Agent packages

Use the following commands to install the SQL Server HA package and SQL Server Agent, if they are not installed already. Installing the HA package after installing SQL Server requires a restart of SQL Server for it to be used. These instructions assume that the repositories for the Microsoft packages have already been set up, since SQL Server should be installed at this point.

RHEL

sudo yum install mssql-server-ha mssql-server-agent
sudo systemctl restart mssql-server

Ubuntu

sudo apt-get install mssql-server-ha mssql-server-agent
sudo systemctl restart mssql-server

SLES

sudo zypper install mssql-server-ha mssql-server-agent
sudo systemctl restart mssql-server

Next steps

In this tutorial, you learned how to deploy a Pacemaker cluster for SQL Server on Linux. You learned how to:

To create and configure an availability group for SQL Server on Linux, see: