HA cluster configuration guide for SAP MaxDB on RHEL

This guide shows you how to deploy an SAP MaxDB system in a Red Hat Enterprise Linux (RHEL) high-availability cluster on Google Cloud, with active/passive cluster configuration.

To deploy a single-node SAP MaxDB system on Linux, use the SAP MaxDB deployment guide.

This guide is intended for advanced SAP MaxDB users who are familiar with Linux HA configurations for SAP systems.

The system that this guide deploys

This guide includes the steps for:

• Configuring an internal passthrough Network Load Balancer to reroute traffic in the event of a failure
• Configuring a Pacemaker cluster on RHEL to manage the SAP systems and other resources during a failover

The deployed cluster includes the following functions and features:

• Two Compute Engine VMs in different zones, able to run an instance of SAP MaxDB
• A Regional Persistent Disk for the installation of SAP MaxDB.
• The Pacemaker high-availability cluster resource manager.
• A STONITH fencing mechanism.

A high-availability installation of SAP NetWeaver is not covered in this guide.

Prerequisites

Before you create the SAP MaxDB high availability cluster, make sure that the following prerequisites are met:

• You have read the SAP MaxDB planning guide.
• You have a Red Hat subscription.
• You or your organization has a Google Cloud account and you have created a project for the SAP MaxDB deployment.

• If you require your SAP workload to run in compliance with data residency, access control, support personnel, or regulatory requirements, then you must create the required Assured Workloads folder. For more information, see Compliance and sovereign controls for SAP on Google Cloud.

• If OS login is enabled in your project metadata, you need to disable OS login temporarily until your deployment is complete. For deployment purposes, this procedure configures SSH keys in instance metadata. When OS login is enabled, metadata-based SSH key configurations are disabled, and this deployment fails. After deployment is complete, you can enable OS login again.

  For more information, see:

  • Enabling or disabling OS Login
  • Add SSH keys to VMs that use metadata-based SSH keys

Creating a network

For security purposes, create a new network. You can control who has access by adding firewall rules or by using another access control method.

If your project has a default VPC network, don't use it. Instead, create your own VPC network so that the only firewall rules in effect are those that you create explicitly.

During deployment, VM instances typically require access to the internet to download Google Cloud's Agent for SAP. If you are using one of the SAP-certified Linux images that are available from Google Cloud, the VM instance also requires access to the internet in order to register the license and to access OS vendor repositories. A configuration with a NAT gateway and with VM network tags supports this access, even if the target VMs do not have external IPs.

To set up networking:

Setting up a NAT gateway

If you need to create one or more VMs without public IP addresses, you need to use network address translation (NAT) to enable the VMs to access the internet. Use Cloud NAT, a Google Cloud distributed, software-defined managed service that lets VMs send outbound packets to the internet and receive any corresponding established inbound response packets. Alternatively, you can set up a separate VM as a NAT gateway.

To create a Cloud NAT instance for your project, see Using Cloud NAT.

After you configure Cloud NAT for your project, your VM instances can securely access the internet without a public IP address.

Adding firewall rules

By default, an implied firewall rule blocks incoming connections from outside your Virtual Private Cloud (VPC) network. To allow incoming connections, set up a firewall rule for your VM. After an incoming connection is established with a VM, traffic is permitted in both directions over that connection.

You can also create a firewall rule to allow external access to specified ports, or to restrict access between VMs on the same network. If the default VPC network type is used, some additional default rules also apply, such as the default-allow-internal rule, which allows connectivity between VMs on the same network on all ports.

Depending on the IT policy that is applicable to your environment, you might need to isolate or otherwise restrict connectivity to your database host, which you can do by creating firewall rules.

Depending on your scenario, you can create firewall rules to allow access for:

• The default SAP ports that are listed in TCP/IP of All SAP Products.
• Connections from your computer or your corporate network environment to your Compute Engine VM instance. If you are unsure of what IP address to use, talk to your company's network administrator.

To create a firewall rule:

$ gcloud compute firewall-rules create firewall-name
--direction=INGRESS --priority=1000 \
--network=network-name --action=ALLOW --rules=protocol:port \
--source-ranges ip-range --target-tags=network-tags

Deploying the VMs and installing MaxDB

Before you begin configuring the HA cluster, you define and deploy the VM instances and SAP MaxDB systems that serve as the primary and secondary nodes in your HA cluster.

Create a VM for MaxDB deployment

As part of the HA deployment, two Google Cloud Compute Engine VMs will need to be created. You can refer to the guide Create and start a Compute Engine instance.

Note that Regional Persistent Disk only supports the use E2, N1, N2, and N2D machine types. See more details on the Regional Persistent Disk guide.

See SAP Note 2456432 - SAP applications on Google Cloud: Supported products and Google Cloud machine types to select the right machine type based on your sizing.

Create the two VMs in separate zones to achieve zonal resilience, with the following minimum requirements:

1. VM details:

   • Instance Name
   • Zone - Your preferred zone
   • Machine Type - Based on sizing
   • Subnet - Subnet name created for this region

2. Service account with at least access scope to the following APIs:

   • https://www.googleapis.com/auth/compute
   • https://www.googleapis.com/auth/servicecontrol
   • https://www.googleapis.com/auth/service.management.readonly
   • https://www.googleapis.com/auth/logging.write
   • https://www.googleapis.com/auth/monitoring.write
   • https://www.googleapis.com/auth/trace.append
   • https://www.googleapis.com/auth/devstorage.read_write

3. Additional disk on each VM with minimum of 20 GB to be used for /usr/sap

Create a single regional disk for SAP MaxDB

For this deployment, one regional disk will be used to hold the MaxDB files within the /sapdb directory.

Create the disk, making sure the replication zones for the regional disk match the zones in which you created the two VMs.

Attach the regional disk to one of the VMs where you will perform the MaxDB installation, and configuration tasks.

Prepare RHEL OS for SAP installation

SAP Product requires specific operating system settings and packages to be installed. Follow the guidelines in SAP Note: 2772999 - Red Hat Enterprise Linux 8.x: Installation and Configuration .

This task must be performed on both nodes.

Create filesystems

1. Connect to both instances using SSH and create the /usr/sap/SID and /sapdb mount points.

   # sudo mkdir -p /usr/sap/SID
   # sudo mkdir -p /sapdb

2. Create the filesystems in the two additional disks attached to the VMs using mkfs.

   Note that at this time the regional disk will only be attached in one of the VMs, hence, the creation of the /sapdb file system will only be done once.

3. Edit the /etc/fstab file to always mount /usr/sap/SID at reboot on both nodes.

4. Manually mount the /sapdb file system into the node where you will perform the MaxDB installation.

   For additional reference on creating and mounting the filesystems, see the guide Format and mount a non-boot disk on a Linux VM.

Modify the LVM configuration

You need to modify the logical volume management (LVM) configuration so the shared volume group (VG) is always only attached and accessible by one node.

To do so, perform the following steps on both nodes:

1. As root, edit the /etc/lvm/lvm.conf file and modify the system_id_source value to uname from none

2. Check the results:

   # grep -i system_id_source /etc/lvm/lvm.conf

   You should see a similar output to the following:

   # Configuration option global/system_id_source.
           system_id_source = "uname"
   

3. Additionally to prevent the VMs from activating cluster-managed VGs when a node reboots, maintain the following parameter in the/etc/lvm/lvm.conf configuration file with comma-separated full VG names that are not managed by the cluster.

   For example, when usrsap is a VG name that is not managed by cluster:

   auto_activation_volume_list = [ usrsap ]

   When there are no VGs that are not managed by cluster, for example, this parameter must be added with empty values:

   auto_activation_volume_list = [  ]

Installing the database and the SAP host agent

Now that your operating system is configured, you can install your SAP MaxDB database and SAP Host Agent. MaxDB is typically installed with the SAP product that it is integrated with.

Note that the installation will only be performed once, in the one which you have attached the Regional Persistent Disk.

To install SAP MaxDB on your VM:

1. Establish an SSH connection to your Linux-based VM.
2. Download the SAP Software Provisioning Manager (SWPM), the SAP product installation media, and MaxDB installation Media according to SAP installation guides.
3. Install your SAP product and SAP MaxDB database according to the SAP installation guides for your SAP product. For additional guidance, see the SAP MaxDB documentation.

SAP provides additional installation information in SAP Note 1020175 - FAQ: SAP MaxDB installation, upgrade or applying a patch.

Once the installation is completed, execute the following validations:

1. As sidadm user, check the status of MaxDB.

   # dbmcli -d  SID -u control,password db_state

   You should see output similar to the following example:

   >dbmcli -d  MDB -u control, my_p4$$w0rd db_state
   OK
   State
   ONLINE
   

2. Check as well the status of x_server:

   # x_server

   You should see output similar to the following example:

   >x_server
   2024-10-23 19:01:43 11968 19744 INF  12916          Found running XServer on port 7200
   2024-10-23 19:01:43 11968 19744 INF  13011            version 'U64/LIX86 7.9.10   Build 004-123-265-969'
   2024-10-23 19:01:43 11968 19744 INF  13010            installation MDB  - path: /sapdb/MDB/db
   2024-10-23 19:01:45 11971 13344 INF  12916          Found running sdbgloballistener on port 7210
   2024-10-23 19:01:45 11971 13344 INF  13011            version 'U64/LIX86 7.9.10   Build 004-123-265-969'
   

3. Check if SAP Host agent is running:

   # ps -ef | grep -i hostctrl

   You should see output similar to the following example:

   >ps -ef | grep -i hostctrl
   root      1543     1  0 Oct18 ?        00:00:15 /usr/sap/hostctrl/exe/saphostexec pf=/usr/sap/hostctrl/exe/host_profile
   sapadm    1550     1  0 Oct18 ?        00:03:00 /usr/sap/hostctrl/exe/sapstartsrv pf=/usr/sap/hostctrl/exe/host_profile -D
   root      1618     1  0 Oct18 ?        00:03:48 /usr/sap/hostctrl/exe/saposcol -l -w60 pf=/usr/sap/hostctrl/exe/host_profile
   mdbadm   12751 11261  0 19:03 pts/0    00:00:00 grep --color=auto -i hostctrl
   

4. Once the Installation is verified, stop MaxDB instance and x_server.

   # dbmcli -d SID -u control, and password db_offline
   # x_server stop
   

Performing post-installation tasks

Before using your SAP MaxDB instance, we recommend that you perform the following post-deployment steps:

1. Update your SAP MaxDB software with the latest patches, if available.
2. Install any additional components.
3. Configure and back up your new SAP MaxDB database.

For more information, see SAP MaxDB Database Administration.

After the SAP MaxDB systems have deployed successfully, you define and configure the HA cluster.

Configure the Cloud Load Balancing failover support

The internal passthrough Network Load Balancer service with failover support routes traffic to the active host in an SAP MaxDB cluster based on a health check service.

Reserve an IP address for the virtual IP

The virtual IP (VIP) address , which is sometimes referred to as a floating IP address, follows the active SAP MaxDB system. The load balancer routes traffic that is sent to the VIP to the VM that is hosting the active SAP MaxDB system.

1. Open Cloud Shell:

   Go to Cloud Shell

2. Reserve an IP address for the virtual IP. This is the IP address that applications use to access SAP MaxDB. If you omit the --addresses flag, an IP address in the specified subnet is chosen for you:

   $ gcloud compute addresses create VIP_NAME \
     --region CLUSTER_REGION --subnet CLUSTER_SUBNET \
     --addresses VIP_ADDRESS

   For more information about reserving a static IP, see Reserving a static internal IP address.

3. Confirm IP address reservation:

   $ gcloud compute addresses describe VIP_NAME \
     --region CLUSTER_REGION

   You should see output similar to the following example:

   address: 10.0.0.19
   addressType: INTERNAL
   creationTimestamp: '2024-10-23T14:19:03.109-07:00'
   description: ''
   id: '8961491304398200872'
   kind: compute#address
   name: vip-for-maxdb-ha
   networkTier: PREMIUM
   purpose: GCE_ENDPOINT
   region: https://www.googleapis.com/compute/v1/projects/example-project-123456/regions/us-central1
   selfLink: https://www.googleapis.com/compute/v1/projects/example-project-123456/regions/us-central1/addresses/vip-for-maxdb-ha
   status: RESERVED
   subnetwork: https://www.googleapis.com/compute/v1/projects/example-project-123456/regions/us-central1/subnetworks/example-subnet-us-central1

Create instance groups for your host VMs

1. In Cloud Shell, create two unmanaged instance groups and assign the primary host VM to one and the secondary host VM to the other:

   $ gcloud compute instance-groups unmanaged create PRIMARY_IG_NAME \
     --zone=PRIMARY_ZONE
   $ gcloud compute instance-groups unmanaged add-instances PRIMARY_IG_NAME \
     --zone=PRIMARY_ZONE \
     --instances=PRIMARY_HOST_NAME
   $ gcloud compute instance-groups unmanaged create SECONDARY_IG_NAME \
     --zone=SECONDARY_ZONE
   $ gcloud compute instance-groups unmanaged add-instances SECONDARY_IG_NAME \
     --zone=SECONDARY_ZONE \
     --instances=SECONDARY_HOST_NAME
   

2. Confirm the creation of the instance groups:

   $ gcloud compute instance-groups unmanaged list

   You should see output similar to the following example:

   NAME          ZONE           NETWORK          NETWORK_PROJECT        MANAGED  INSTANCES
   maxdb-ha-ig-1  us-central1-a  example-network  example-project-123456 No       1
   maxdb-ha-ig-2  us-central1-c  example-network  example-project-123456 No       1

Create a Compute Engine health check

1. In Cloud Shell, create the health check. For the port used by the health check, choose a port that is in the private range, 49152-65535, to avoid clashing with other services. The check-interval and timeout values are slightly longer than the defaults so as to increase failover tolerance during Compute Engine live migration events. You can adjust the values, if necessary:

   $ gcloud compute health-checks create tcp HEALTH_CHECK_NAME --port=HEALTHCHECK_PORT_NUM \
     --proxy-header=NONE --check-interval=10 --timeout=10 --unhealthy-threshold=2 \
     --healthy-threshold=2

2. Confirm the creation of the health check:

   $ gcloud compute health-checks describe HEALTH_CHECK_NAME

   You should see output similar to the following example:

   checkIntervalSec: 10
   creationTimestamp: '2023-10-23T21:03:06.924-07:00'
   healthyThreshold: 2
   id: '4963070308818371477'
   kind: compute#healthCheck
   name: maxdb-health-check
   selfLink: https://www.googleapis.com/compute/v1/projects/example-project-123456/global/healthChecks/maxdb-health-check
   tcpHealthCheck:
    port: 60000
    portSpecification: USE_FIXED_PORT
    proxyHeader: NONE
   timeoutSec: 10
   type: TCP
   unhealthyThreshold: 2

Create a firewall rule for the health checks

Define a firewall rule for a port in the private range that allows access to your host VMs from the IP ranges that are used by Compute Engine health checks, 35.191.0.0/16 and 130.211.0.0/22. For more information, see Creating firewall rules for health checks.

1. If you don't already have one, add a network tag to your host VMs. This network tag is used by the firewall rule for health checks.

   $ gcloud compute instances add-tags PRIMARY_HOST_NAME \
     --tags NETWORK_TAGS \
     --zone PRIMARY_ZONE
   $ gcloud compute instances add-tags SECONDARY_HOST_NAME \
     --tags NETWORK_TAGS \
     --zone SECONDARY_ZONE
   

2. If you don't already have one, create a firewall rule to allow the health checks:

   $ gcloud compute firewall-rules create RULE_NAME \
     --network NETWORK_NAME \
     --action ALLOW \
     --direction INGRESS \
     --source-ranges 35.191.0.0/16,130.211.0.0/22 \
     --target-tags NETWORK_TAGS \
     --rules tcp:HLTH_CHK_PORT_NUM

   For example:

   gcloud compute firewall-rules create  fw-allow-health-checks \
   --network example-network \
   --action ALLOW \
   --direction INGRESS \
   --source-ranges 35.191.0.0/16,130.211.0.0/22 \
   --target-tags cluster-ntwk-tag \
   --rules tcp:60000

Configure the load balancer and failover group

1. Create the load balancer backend service:

   $ gcloud compute backend-services create BACKEND_SERVICE_NAME \
     --load-balancing-scheme internal \
     --health-checks HEALTH_CHECK_NAME \
     --no-connection-drain-on-failover \
     --drop-traffic-if-unhealthy \
     --failover-ratio 1.0 \
     --region CLUSTER_REGION \
     --global-health-checks

2. Add the primary instance group to the backend service:

   $ gcloud compute backend-services add-backend BACKEND_SERVICE_NAME \
     --instance-group PRIMARY_IG_NAME \
     --instance-group-zone PRIMARY_ZONE \
     --region CLUSTER_REGION

3. Add the secondary, failover instance group to the backend service:

   $ gcloud compute backend-services add-backend BACKEND_SERVICE_NAME \
     --instance-group SECONDARY_IG_NAME \
     --instance-group-zone SECONDARY_ZONE \
     --failover \
     --region CLUSTER_REGION

4. Create a forwarding rule. For the IP address, specify the IP address that you reserved for the VIP. If you need to access the SAP MaxDB system from outside of the region that is specified below, include the flag --allow-global-access in the definition:

   $ gcloud compute forwarding-rules create RULE_NAME \
     --load-balancing-scheme internal \
     --address VIP_ADDRESS \
     --subnet CLUSTER_SUBNET \
     --region CLUSTER_REGION \
     --backend-service BACKEND_SERVICE_NAME \
     --ports ALL

   For more information about cross-region access to your SAP MaxDB high-availability system, see Internal TCP/UDP Load Balancing.

Test the load balancer configuration

Even though your backend instance groups won't register as healthy until later, you can test the load balancer configuration by setting up a listener to respond to the health checks. After setting up a listener, if the load balancer is configured correctly, the status of the backend instance groups changes to healthy.

The following sections present different methods that you can use to test the configuration.

Testing the load balancer with the socat utility

You can use the socat utility to temporarily listen on the health check port.

1. On both host VMs, install the socat utility:

   $ sudo yum install -y socat

2. Start a socat process to listen for 60 seconds on the health check port:

   $ sudo timeout 60s socat - TCP-LISTEN:HLTH_CHK_PORT_NUM,fork

3. In Cloud Shell, after waiting a few seconds for the health check to detect the listener, check the health of your backend instance groups:

   $ gcloud compute backend-services get-health BACKEND_SERVICE_NAME \
     --region CLUSTER_REGION

   You should see output similar to the following:

   ---
   backend: https://www.googleapis.com/compute/v1/projects/example-project-123456/zones/us-central1-a/instanceGroups/maxdb-ha-ig-1
   status:
    healthStatus:
    ‐ healthState: HEALTHY
      instance: https://www.googleapis.com/compute/v1/projects/example-project-123456/zones/us-central1-a/instances/maxdb-ha-vm-1
      ipAddress: 10.0.0.35
      port: 80
    kind: compute#backendServiceGroupHealth
   ---
   backend: https://www.googleapis.com/compute/v1/projects/example-project-123456/zones/us-central1-c/instanceGroups/maxdb-ha-ig-2
   status:
    healthStatus:
    ‐ healthState: HEALTHY
      instance: https://www.googleapis.com/compute/v1/projects/example-project-123456/zones/us-central1-c/instances/maxdb-ha-vm-2
      ipAddress: 10.0.0.34
      port: 80
    kind: compute#backendServiceGroupHealth

Testing the load balancer using port 22

If port 22 is open for SSH connections on your host VMs, you can temporarily edit the health checker to use port 22, which has a listener that can respond to the health checker.

To temporarily use port 22, follow these steps:

1. Click your health check in the console:

   Go to Health checks page

2. Click Edit.

3. In the Port field, change the port number to 22.

4. Click Save and wait a minute or two.

5. In Cloud Shell, check the health of your backend instance groups:

   $ gcloud compute backend-services get-health BACKEND_SERVICE_NAME \
     --region CLUSTER_REGION

   You should see output similar to the following:

   ---
   backend: https://www.googleapis.com/compute/v1/projects/example-project-123456/zones/us-central1-a/instanceGroups/maxdb-ha-ig-1
   status:
    healthStatus:
    ‐ healthState: HEALTHY
      instance: https://www.googleapis.com/compute/v1/projects/example-project-123456/zones/us-central1-a/instances/maxdb-ha-vm-1
      ipAddress: 10.0.0.35
      port: 80
    kind: compute#backendServiceGroupHealth
   ---
   backend: https://www.googleapis.com/compute/v1/projects/example-project-123456/zones/us-central1-c/instanceGroups/maxdb-ha-ig-2
   status:
    healthStatus:
    ‐ healthState: HEALTHY
      instance: https://www.googleapis.com/compute/v1/projects/example-project-123456/zones/us-central1-c/instances/maxdb-ha-vm-2
      ipAddress: 10.0.0.34
      port: 80
    kind: compute#backendServiceGroupHealth

6. When you are done, change the health check port number back to the original port number.

Set up Pacemaker

The following procedure configures the Red Hat implementation of a Pacemaker cluster on Compute Engine VMs for SAP MaxDB.

The procedure is based on Red Hat documentation for configuring high-availability clusters, including:

• Installing and Configuring a Red Hat Enterprise Linux 7.6 (and later) High-Availability Cluster on Google Cloud

Install the cluster agents on both nodes

Complete the following steps on both nodes.

1. As root, install the Pacemaker components:

   # yum -y install pcs pacemaker fence-agents-gce resource-agents-gcp resource-agents-sap-hana
   # yum update -y

   If you are using a Google-provided RHEL-for-SAP image, these packages are already installed, but some updates might be required.

2. Set the password for the hacluster user, which is installed as part of the packages:

   # passwd hacluster

3. Specify a password for hacluster at the prompts.

4. In the RHEL images provided by Google Cloud, the OS firewall service is active by default. Configure the firewall service to allow high-availability traffic:

   # firewall-cmd --permanent --add-service=high-availability

   # firewall-cmd --reload

5. Start the pcs service and configure it to start at boot time:

   # systemctl start pcsd.service
   # systemctl enable pcsd.service

6. Check the status of the pcs service:

   # systemctl status pcsd.service

   You should see output similar to the following:

   ● pcsd.service - PCS GUI and remote configuration interface
     Loaded: loaded (/usr/lib/systemd/system/pcsd.service; enabled; vendor preset: disabled)
     Active: active (running) since Sat 2023-10-23 21:17:05 UTC; 25s ago
       Docs: man:pcsd(8)
             man:pcs(8)
   Main PID: 31627 (pcsd)
     CGroup: /system.slice/pcsd.service
             └─31627 /usr/bin/ruby /usr/lib/pcsd/pcsd
   Oct 23 21:17:03 maxdb-ha-vm-1 systemd[1]: Starting PCS GUI and remote configuration interface...
   Oct 23 21:17:05 maxdb-ha-vm-1 systemd[1]: Started PCS GUI and remote configuration interface.

7. Ensure all the required HA services are enabled and up and running on both nodes.

   # systemctl enable pcsd.service pacemaker.service corosync.service

8. In the /etc/hosts file, add the full hostname and the internal IP addresses of both hosts in the cluster. For example:

   127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
   ::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
   10.0.0.40 maxdb-ha-vm-1.us-central1-a.c.example-project-123456.internal maxdb-ha-vm-1  # Added by Google
   10.0.0.41 maxdb-ha-vm-2.us-central1-c.c.example-project-123456.internal maxdb-ha-vm-2
   169.254.169.254 metadata.google.internal  # Added by Google

   For more information from Red Hat about setting up the /etc/hosts file on RHEL cluster nodes, see https://access.redhat.com/solutions/81123.

Create the cluster

1. As root on either node, authorize the hacluster user. Click the tab for your RHEL version to see the command:

   RHEL 8 and later

   # pcs host auth primary-host-name secondary-host-name

   RHEL 7

   # pcs cluster auth primary-host-name secondary-host-name

2. At the prompts, enter the hacluster username and the password that you set for the hacluster user.

3. Create the cluster:

   RHEL 8 and later

   # pcs cluster setup cluster-name primary-host-name secondary-host-name

   RHEL 7

   # pcs cluster setup --name cluster-name primary-host-name secondary-host-name

Edit the corosync.conf default settings

Edit the /etc/corosync/corosync.conf file on the primary host to set a more appropriate starting point for testing the fault tolerance of your HA cluster on Google Cloud.

1. On either host, use your preferred text editor to open the /etc/corosync/corosync.conf file for editing:

   # /etc/corosync/corosync.conf

2. If /etc/corosync/corosync.conf is a new file or is empty, you can check the /etc/corosync/ directory for an example file to use as the base for the corosync file.

3. In the totem section of the corosync.conf file, add the following properties with the suggested values as shown for your RHEL version:

   RHEL 8 and later

   • transport: knet
   • token: 20000
   • token_retransmits_before_loss_const: 10
   • join: 60
   • max_messages: 20

   For example:

   totem {
   version: 2
   cluster_name: hacluster
   secauth: off
   transport: knet
   token: 20000
   token_retransmits_before_loss_const: 10
   join: 60
   max_messages: 20
   }
   ...

   RHEL 7

   • transport: udpu
   • token: 20000
   • token_retransmits_before_loss_const: 10
   • join: 60
   • max_messages: 20

   For example:

   totem {
   version: 2
   cluster_name: hacluster
   secauth: off
   transport: udpu
   token: 20000
   token_retransmits_before_loss_const: 10
   join: 60
   max_messages: 20
   }
   ...

4. From the host that contains the edited corosync.conf file, sync the corosync configuration across the cluster:

   RHEL 8 and later

   # pcs cluster sync corosync

   RHEL 7

   # pcs cluster sync

5. Set the cluster to start automatically:

   # pcs cluster enable --all

   # pcs cluster start --all

6. Confirm that the new corosync settings are active in the cluster by using the corosync-cmapctl utility:

   # corosync-cmapctl

Set up fencing

RHEL images that are provided by Google Cloud include a fence_gce fencing agent that is specific to Google Cloud. You use fence_gce to create fence devices for each host VM.

To ensure the correct sequence of events after a fencing action, you configure the operating system to delay the restart of Corosync after a VM is fenced. You also adjust the Pacemaker timeout for reboots to account for the delay.

To see all of the options that are available with the fence_gce fencing agent, issue fence_gce -h.

Create the fencing device resources

1. On the primary host as root:

   1. Create a fencing device for each host VM:

      # pcs stonith create primary-fence-name fence_gce \
        port=primary-host-name \
        zone=primary-host-zone \
        project=project-id \
        pcmk_reboot_timeout=300 pcmk_monitor_retries=4 pcmk_delay_max=30 \
        op monitor interval="300s" timeout="120s" \
        op start interval="0" timeout="60s"
      # pcs stonith create secondary-fence-name fence_gce \
        port=secondary-host-name \
        zone=secondary-host-zone \
        project=project-id \
        pcmk_reboot_timeout=300 pcmk_monitor_retries=4 \
        op monitor interval="300s" timeout="120s" \
        op start interval="0" timeout="60s"

   2. Constrain each fence device to the other host VM:

      # pcs constraint location primary-fence-name avoids primary-host-name
      # pcs constraint location secondary-fence-name avoids secondary-host-name

2. On the primary host as root, test the secondary fence device:

   1. Shut down the secondary host VM:

      # fence_gce -o off -n secondary-host-name --zone=secondary-host-zone

      If the command is successful, you lose connectivity to the secondary host VM and it appears stopped on the VM instances page in the Google Cloud console. You might need to refresh the page.

   2. Restart the secondary host VM:

      # fence_gce -o on -n secondary-host-name --zone=secondary-host-zone

3. On the secondary host as root, test the primary fence device by repeating the preceding steps using the values for the primary host in the commands.

4. On either host as root, check the status of the cluster:

   # pcs status

   The fence resources appear in the resources section of the cluster status, similar to the following example:

   [root@maxdb-ha-vm-2 ~]# pcs status
   Cluster name: maxdb-ha-cluster
   Stack: corosync
   Current DC: maxdb-ha-vm-1 (version 1.1.19-8.el7_6.5-c3c624ea3d) - partition with quorum
   Last updated: Mon Jun 15 17:19:07 2020
   Last change: Mon Jun 15 17:18:33 2020 by root via cibadmin on maxdb-ha-vm-1
   
   2 nodes configured
   2 resources configured
   
   Online: [ maxdb-ha-vm-1 maxdb-ha-vm-2 ]
   
   Full list of resources:
   
    STONITH-maxdb-ha-vm-1   (stonith:fence_gce):    Started maxdb-ha-vm-2
    STONITH-maxdb-ha-vm-2   (stonith:fence_gce):    Started maxdb-ha-vm-1
   
   Daemon Status:
     corosync: active/enabled
     pacemaker: active/enabled
     pcsd: active/enabled

Set a delay for the restart of Corosync

1. On both hosts as root, create a systemd drop-in file that delays the startup of Corosync to ensure the proper sequence of events after a fenced VM is rebooted:

   systemctl edit corosync.service

2. Add the following lines to the file:

   [Service]
   ExecStartPre=/bin/sleep 60

3. Save the file and exit the editor.

4. Reload the systemd manager configuration.

   systemctl daemon-reload

5. Confirm the drop-in file was created:

   service corosync status

   You should see a line for the drop-in file, as shown in the following example:

   ● corosync.service - Corosync Cluster Engine
      Loaded: loaded (/usr/lib/systemd/system/corosync.service; disabled; vendor preset: disabled)
     Drop-In: /etc/systemd/system/corosync.service.d
              └─override.conf
      Active: active (running) since Tue 2021-07-20 23:45:52 UTC; 2 days ago

Install listeners and create a health check resource

To configure a health check resource, you need to install the listeners first.

Install a listener

The load balancer uses a listener on the health-check port of each host to determine where the MaxDB instance is running.

1. As root on the both hosts, install a TCP listener. These instructions install and use HAProxy as the listener.

   # yum install haproxy

2. Open the configuration file haproxy.cfg for editing:

   # vi /etc/haproxy/haproxy.cfg

   1. In the defaults section of the haproxy.cfg, change the mode to tcplog.

   2. After the defaults section, create a new section by adding:

      #---------------------------------------------------------------------
      # Health check listener port for SAP MaxDB HA cluster
      #---------------------------------------------------------------------
      listen healthcheck
        bind *:healthcheck-port-num

      The bind port is the same port that you used when you created the health check.

      When you are done, your updates should look similar to the following example:

      #---------------------------------------------------------------------
      # common defaults that all the 'listen' and 'backend' sections will
      # use if not designated in their block
      #---------------------------------------------------------------------
      defaults
        mode                    tcp
        log                     global
        option                  tcplog
        option                  dontlognull
        option http-server-close
        # option forwardfor       except 127.0.0.0/8
        option                  redispatch
        retries                 3
        timeout http-request    10s
        timeout queue           1m
        timeout connect         10s
        timeout client          1m
        timeout server          1m
        timeout http-keep-alive 10s
        timeout check           10s
        maxconn                 3000
      
      #---------------------------------------------------------------------
      # Set up health check listener for SAP MaxDB HA cluster
      #---------------------------------------------------------------------
      listen healthcheck
       bind *:60000

3. On each host as root, start the service to confirm it is correctly configured:

   # systemctl start haproxy.service

4. On the Load balancer page in the Google Cloud console, click your load balancer entry:

   Load balancing page

   In the Backend section on the Load balancer details page, if the HAProxy service is active on both hosts, you see 1/1 in the Healthy column of each instance group entry.

5. On each host, stop the HAProxy service:

   # systemctl stop haproxy.service

   After you stop the HAProxy service on each host, 0/1 displays in the Healthy column of each instance group.

   Later, when the health check is configured, the cluster restarts the listener on the active node.

Create the health check resource

1. On either host as root, create a health check resource for the HAProxy service:

   # pcs resource create healthcheck_resource_name service:haproxy op monitor interval=10s timeout=20s —-group SAPMaxDB_Group

2. Confirm that the health check service is active on the same host as your SAP MaxDB instance:

   # pcs status

   If the health check resource is not on the same host were the MaxDB is, move it with the following command:

   # pcs resource move healthcheck_resource_name target_host_name
   # pcs resource clear healthcheck_resource_name

   The command pcs resource clear leaves the resource at its new location but removes the unwanted location constraint that the pcs resource move command created.

   In the status, the resources section should look similar to the following example:

   Full list of resources:
   
   STONITH-maxdb-ha-vm-1   (stonith:fence_gce):    Started maxdb-ha-vm-2
   STONITH-maxdb-ha-vm-2   (stonith:fence_gce):    Started maxdb-ha-vm-1
   
   Resource Group: SAPMaxDB_Group
     rsc_healthcheck_MDB    (service:haproxy):      Started maxdb-ha-vm-1

Set the cluster defaults

Set up migration thresholds and stickiness to determine the number of failovers to attempt before failure and to set the system to try restarting on the current host first. This only needs to be set on one node to apply to the cluster.

1. As root on either host, set the resource defaults:

   # pcs resource defaults resource-stickiness=1000
   # pcs resource defaults migration-threshold=5000

   The property resource-stickiness controls how likely a service is to stay running where it is. Higher values make the service more sticky. A value of 1000 means that the service is very sticky.

   The property migration-threshold specifies the number of failures that must occur before a service fails over to another host. A value of 5000 is high enough to prevent failover for shorter-lived error situations.

   You can check the resource defaults by entering pcs resource defaults.

2. Set the resource operation timeout defaults:

   # pcs resource op defaults timeout=600s

   You can check the resource op defaults by entering pcs resource op defaults.

3. Set the following cluster properties:

   # pcs property set stonith-enabled="true"
   # pcs property set stonith-timeout="300s"
   

   You can check your property settings with pcs property list.

Create MaxDB resources in the cluster

Before performing these steps, make sure MaxDB and x_server is stopped and /sapdb file system is unmounted.

Create gcp-pd-move resource

The gcp-pd-move resource is a resource agent that is used to move the persistent disk from one node to another during a cluster failover.

1. Create the resource using the following command as root on either node:

   # pcs resource create pd_move_resource_name gcp-pd-move \
     disk_name=regional_pd_name mode="READ_WRITE" disk_scope=regional \
     op monitor interval=10s timeout=15s \
     op start interval=0s timeout=300s \
     op stop interval=0s timeout=15s \
     --group SAPMaxDB_Group

Create LVM resource

An LVM-activated resource agent is used to activate the LVM after the disk is moved to the other node.

1. Create the LVM resource using the following command as root on either node:

   # pcs resource create lvm_resource_name LVM-activate \
     vgname=vgname_for_maxdb \
     vg_access_mode=system_id activation_mode=exclusive \
     --group SAPMaxDB_Group

   For example:

   # pcs resource create sapdb_lvm LVM-activate \
     vgname=sapdb vg_access_mode=system_id \
     activation_mode=exclusive \
     --group SAPMaxDB_Group

Create the file system resource

File system resource is used in the cluster to unmount /sapdb and mount it on another node during the failover operation.

1. Create the file system resource using the following command as root on either node:

   # pcs resource create fs_resource_name Filesystem \
     device=filesystem directory=/sapdb fstype=fs_type \
     --group SAPMaxDB_Group

   For example:

   # pcs resource create sapdb_FS Filesystem \
     device=/dev/mapper/sapdb-sapdblv directory=/sapdb fstype=ext4 \
     --group SAPMaxDB_Group

Preparations for MaxDB resource group

To enable the MaxDB resource group, you need to perform the following steps.

1. Sync users and groups from the node on which you have performed the MaxDB installation to the other node.

   1. The SAP MaxDB users must be synced between nodes by copying the entries in /etc/passwd, for example:

       sdb:x:1002:1003:MaxDB User:/home/sdb:/bin/false
       madbadm:x:1003:1005:SAP System Administrator:/home/mdbadm:/bin/csh

   2. Similarly, the SAP groups must be synced as well by copying the entries in /etc/group from one node to the other, for example:

       dba:x:1003:mdbadm
       sapsys:x:1005:

2. Sync MaxDB specific files that get stored under the operating system directories. As root user, execute the following commands:

   # rsync -av /etc/services target_host:/etc/services
   # rsync -av /home/* target_host:/home
   # rsync -av --exclude=sapservices /usr/sap/* target_host:/usr/sap
   # rsync -av --ignore-existing /usr/sap/sapservicestarget_host:/usr/sap/sapservices
   # rsync -av /etc/init.d/sapinittarget_host:/etc/init.d/

   # MaxDB specific files
   # rsync -av /etc/opttarget_host:/etc
   # rsync -av /var/lib/sdbtarget_host:/var/lib

3. For the SAP OS users on the second node, rename the following environment files to use its respective hostname in their home directories, for example:

   mv .sapenv_maxdb-ha-vm-1.sh .sapenv_maxdb-ha-vm-2.sh
   mv .sapenv_maxdb-ha-vm-1.csh .sapenv_maxdb-ha-vm-2.csh
   mv .sapsrc_maxdb-ha-vm-1.sh  .sapsrc_maxdb-ha-vm-2.sh
   mv .sapsrc_maxdb-ha-vm-1.csh  .sapsrc_maxdb-ha-vm-2.csh
   mv .dbenv_maxdb-ha-vm-1.sh .sapenv_maxdb-ha-vm-2.sh
   mv .dbenv_maxdb-ha-vm-1.csh .dbenv_maxdb-ha-vm-2.csh

The SAPDatabase resource agent does not use any DB specific commands to stop or start the database but relies upon saphostctrl commands to perform the same. SAP Host Agent requires xuser entries to be created for successful monitoring and control of MAXDB using saphostctrl. See SAP Note 2435938 - SAP Host Agent SAP MaxDB: DBCredentials for DB connect for more information.

1. As root, execute the following command to SetDatabaseProperty on the active node:

   /usr/sap/hostctrl/exe/saphostctrl -host primary-host-name -user sapadm password \
     -dbname SID -dbtype ada -function SetDatabaseProperty DBCredentials=SET \
     -dboption User=SUPERDBA -dboption Password=password

   Test the entries using the following command, even if the database is stopped the command should be able to bring the status back:

   /usr/sap/hostctrl/exe/saphostctrl -host secondary-host-name -dbname SID \
     -dbtype ada -function GetDatabaseStatus

The saphostctrl agent command uses the xuser program from MaxDB installation and hence to prepare the second node now, you will move the SAPMaxDB_group to maxdb-node-b.

1. On any node execute the following command as root:

   pcs resource move SAPMaxDB_group

Observe that the four created resources, Health check, gcp-pd-move, LVM and File System are now migrated and successfully started on the second node.

1. You can use the following command on any node to watch the actions being performed:

   watch pcs status

Once all four resources are successfully started on the second node, perform the saphostctrl command.

1. As root, execute the following command to SetDatabaseProperty on the now active node:

   /usr/sap/hostctrl/exe/saphostctrl -host secondary-host-name -user sapadm password \
     -dbname SID -dbtype ada -function SetDatabaseProperty DBCredentials=SET \
     -dboption User=SUPERDBA -dboption Password=password

2. On the node b, manually start MaxDB and x_server to check if they can be started properly:

   # dbmcli -d SID -u control, and password db_online
   # x_server start
   

Proceed to the next step of creating a resource for the SAP database. If any errors are observed at this point, don't create the database resource.

Create resource for SAP MaxDB

RHEL Pacemaker uses the SAP database resource agent to monitor and control the SAP database.

1. Create the database resource on the node where SAPMaxDB_group is active using the following command:

   # pcs resource create SAPDatabase_resource_name SAPDatabase \
     DBTYPE="ADA" SID="SID" STRICT_MONITORING="TRUE" \
     MONITOR_SERVICES="Database|x_server" AUTOMATIC_RECOVER="TRUE"
     --group SAPMaxDB_Group

   The final cluster resources can be seen using pcs status and the expected result is as follows:

   # pcs status
     Cluster name: maxdb-cluster
     Stack: corosync
     Current DC: maxdb-ha-vm-1 (version 1.1.23-1.el7_9.1-9acf116022) - partition with quorum
     Last updated: Wed Oct 23 02:04:32 2024
     Last change: Wed Oct 23 02:01:41 2024 by hacluster via crmd on maxdb-ha-vm-1
   
     2 nodes configured
     7 resource instances configured
   
     Online: [ maxdb-ha-vm-1 maxdb-ha-vm-2 ]
   
     Full list of resources:
   
     STONITH-maxdb-ha-vm-1  (stonith:fence_gce):    Started maxdb-ha-vm-2
     STONITH-maxdb-ha-vm-2  (stonith:fence_gce):    Started maxdb-ha-vm-1
     Resource Group: SAPMaxDB_Group
        healthcheck_maxdb  (service:haproxy):      Started maxdb-ha-vm-1
        sapdb_regpd        (ocf::heartbeat:gcp-pd-move):   Started maxdb-ha-vm-1
        lvm_sapdb  (ocf::heartbeat:LVM-activate):  Started maxdb-ha-vm-1
        sapdb_fs   (ocf::heartbeat:Filesystem):    Started maxdb-ha-vm-1
        MDB_SAPMaxDB       (ocf::heartbeat:SAPDatabase):   Started maxdb-ha-vm-1
   
     Daemon Status:
     corosync: active/enabled
     pacemaker: active/enabled
     pcsd: active/enabled

Test failover

Test your cluster by simulating a failure on the active host. Use a test system or run the test on your production system before you release the system for use.

Backup the system before the test.

You can simulate a failure in a variety of ways, including:

• Manually stop MaxDB or x_server
• Kill MaxDB or x_server process
• reboot (on the active node)
• ip link set eth0 down for instances with a single network interface
• iptables ... DROP for instances with multiple network interfaces
• echo c > /proc/sysrq-trigger

These instructions use ip link set eth0 down or iptables to simulate a network disruption between your two hosts in the cluster. Use the ip link command on an instance with a single network interface and use the iptables command on instances with one or more network interfaces. The test validates both failover as well as fencing. In the case where your instances have multiple network interfaces defined, you use the iptables command on the secondary host to drop incoming and outgoing traffic based on the IP used by the primary host for cluster communication, thereby simulating a network connection loss to the primary.

1. On the active host, as root, take the network interface offline:

   # ip link set eth0 down

2. Reconnect to either host using SSH and change to the root user.

3. Enter pcs status to confirm that the previously passive host has now the Regional Persistent Disk attached and is running the MaxDB services. Automatic restart is enabled in the cluster, so the stopped host will restart and assume the role of passive host, as shown in the following example:

   Cluster name: maxdb-ha-cluster
   Stack: corosync
   Current DC: maxdb-ha-vm-2 (version 1.1.23-1.el7_9.1-9acf116022) - partition with quorum
   Last updated: Wed Oct 23 02:01:45 2024
   Last change: Wed Oct 23 02:01:41 2024 by hacluster via crmdon maxdb-ha-vm-2
   
   2 nodes configured
   7 resources configured
   
   Online: [ maxdb-ha-vm-1 maxdb-ha-vm-2 ]
   
   Full list of resources:
   
   STONITH-maxdb-ha-vm-1   (stonith:fence_gce):    Started maxdb-ha-vm-2
   STONITH-maxdb-ha-vm-2   (stonith:fence_gce):    Started maxdb-ha-vm-1
   
   Resource Group: SAPMaxDB_Group
    healthcheck_maxdb  (service:haproxy):      Started maxdb-ha-vm-2
    sapdb_regpd        (ocf::heartbeat:gcp-pd-move):   Started maxdb-ha-vm-2
    lvm_sapdb  (ocf::heartbeat:LVM-activate):  Started maxdb-ha-vm-2
    sapdb_fs   (ocf::heartbeat:Filesystem):    Started maxdb-ha-vm-2
    MDB_SAPMaxDB       (ocf::heartbeat:SAPDatabase):   Started maxdb-ha-vm-2
   
   Daemon Status:
    corosync: active/enabled
    pacemaker: active/enabled
    pcsd: active/enabled

Troubleshoot

To troubleshoot problems with high-availability configurations for SAP systems on RHEL, see Troubleshooting high-availability configurations for SAP.

Get support for SAP HANA on RHEL

If you need help resolving a problem with high-availability clusters for SAP HANA on RHEL, then gather the required diagnostic information and contact Cloud Customer Care. For more information, see High-availability clusters on RHEL diagnostic information.