Chapter 50. Configuring an active/passive Apache HTTP server in a Red Hat High Availability cluster

Procedure

1. On both nodes of the cluster, perform the following steps to set the value for the LVM system ID to the value of the uname identifier for the system. The LVM system ID will be used to ensure that only the cluster is capable of activating the volume group.

   1. Set the system_id_source configuration option in the /etc/lvm/lvm.conf configuration file to uname.

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

   2. Verify that the LVM system ID on the node matches the uname for the node.

      # lvm systemid
        system ID: z1.example.com
      # uname -n
        z1.example.com

2. Create the LVM volume and create an XFS file system on that volume. Since the /dev/sdb1 partition is storage that is shared, you perform this part of the procedure on one node only.

   Note

   If your LVM volume group contains one or more physical volumes that reside on remote block storage, such as an iSCSI target, Red Hat recommends that you ensure that the service starts before Pacemaker starts. For information about configuring startup order for a remote physical volume used by a Pacemaker cluster, see Configuring startup order for resource dependencies not managed by Pacemaker.

   1. Create an LVM physical volume on partition /dev/sdb1.

      [root@z1 ~]# pvcreate /dev/sdb1
        Physical volume "/dev/sdb1" successfully created

      Note

      If your LVM volume group contains one or more physical volumes that reside on remote block storage, such as an iSCSI target, Red Hat recommends that you ensure that the service starts before Pacemaker starts. For information about configuring startup order for a remote physical volume used by a Pacemaker cluster, see Configuring startup order for resource dependencies not managed by Pacemaker.

   2. Create the volume group my_vg that consists of the physical volume /dev/sdb1.

      For RHEL 8.5 and later, specify the --setautoactivation n flag to ensure that volume groups managed by Pacemaker in a cluster will not be automatically activated on startup. If you are using an existing volume group for the LVM volume you are creating, you can reset this flag with the vgchange --setautoactivation n command for the volume group.

      [root@z1 ~]# vgcreate --setautoactivation n my_vg /dev/sdb1
        Volume group "my_vg" successfully created

      For RHEL 8.4 and earlier, create the volume group with the following command.

      [root@z1 ~]# vgcreate my_vg /dev/sdb1
        Volume group "my_vg" successfully created

      For information on ensuring that volume groups managed by Pacemaker in a cluster will not be automatically activated on startup for RHEL 8.4 and earlier, see Ensuring a volume group is not activated on multiple cluster nodes.

   3. Verify that the new volume group has the system ID of the node on which you are running and from which you created the volume group.

      [root@z1 ~]# vgs -o+systemid
        VG    #PV #LV #SN Attr   VSize  VFree  System ID
        my_vg   1   0   0 wz--n- <1.82t <1.82t z1.example.com

   4. Create a logical volume using the volume group my_vg.

      [root@z1 ~]# lvcreate -L450 -n my_lv my_vg
        Rounding up size to full physical extent 452.00 MiB
        Logical volume "my_lv" created

      You can use the lvs command to display the logical volume.

      [root@z1 ~]# lvs
        LV      VG      Attr      LSize   Pool Origin Data%  Move Log Copy%  Convert
        my_lv   my_vg   -wi-a---- 452.00m
        ...

   5. Create an XFS file system on the logical volume my_lv.

      [root@z1 ~]# mkfs.xfs /dev/my_vg/my_lv
      meta-data=/dev/my_vg/my_lv       isize=512    agcount=4, agsize=28928 blks
               =                       sectsz=512   attr=2, projid32bit=1
      ...

3. If you are using an LVM devices file, supported in RHEL 8.5 and later, add the shared device to the devices file on the second node of the cluster.

   [root@z2 ~]# lvmdevices --adddev /dev/sdb1

1. Determine which volume groups are currently configured on your local storage with the following command. This will output a list of the currently-configured volume groups. If you have space allocated in separate volume groups for root and for your home directory on this node, you will see those volumes in the output, as in this example.

   # vgs --noheadings -o vg_name
     my_vg
     rhel_home
     rhel_root

2. Add the volume groups other than my_vg (the volume group you have just defined for the cluster) as entries to auto_activation_volume_list in the /etc/lvm/lvm.conf configuration file.

   For example, if you have space allocated in separate volume groups for root and for your home directory, you would uncomment the auto_activation_volume_list line of the lvm.conf file and add these volume groups as entries to auto_activation_volume_list as follows. Note that the volume group you have just defined for the cluster (my_vg in this example) is not in this list.

   auto_activation_volume_list = [ "rhel_root", "rhel_home" ]

   Note

   If no local volume groups are present on a node to be activated outside of the cluster manager, you must still initialize the auto_activation_volume_list entry as auto_activation_volume_list = [].

3. Rebuild the initramfs boot image to guarantee that the boot image will not try to activate a volume group controlled by the cluster. Update the initramfs device with the following command. This command may take up to a minute to complete.

   # dracut -H -f /boot/initramfs-$(uname -r).img $(uname -r)

4. Reboot the node.

   Note

   If you have installed a new Linux kernel since booting the node on which you created the boot image, the new initrd image will be for the kernel that was running when you created it and not for the new kernel that is running when you reboot the node. You can ensure that the correct initrd device is in use by running the uname -r command before and after the reboot to determine the kernel release that is running. If the releases are not the same, update the initrd file after rebooting with the new kernel and then reboot the node.

5. When the node has rebooted, check whether the cluster services have started up again on that node by executing the pcs cluster status command on that node. If this yields the message Error: cluster is not currently running on this node then enter the following command.

   # pcs cluster start

   Alternately, you can wait until you have rebooted each node in the cluster and start cluster services on all of the nodes in the cluster with the following command.

   # pcs cluster start --all

Procedure

1. Ensure that the Apache HTTP Server is installed on each node in the cluster. You also need the wget tool installed on the cluster to be able to check the status of the Apache HTTP Server.

   On each node, execute the following command.

   # yum install -y httpd wget

   If you are running the firewalld daemon, on each node in the cluster enable the ports that are required by the Red Hat High Availability Add-On and enable the ports you will require for running httpd. This example enables the httpd ports for public access, but the specific ports to enable for httpd may vary for production use.

   # firewall-cmd --permanent --add-service=http
   # firewall-cmd --permanent --zone=public --add-service=http
   # firewall-cmd --reload

2. In order for the Apache resource agent to get the status of Apache, on each node in the cluster create the following addition to the existing configuration to enable the status server URL.

   # cat <<-END > /etc/httpd/conf.d/status.conf
   <Location /server-status>
       SetHandler server-status
       Require local
   </Location>
   END

3. When you use the apache resource agent to manage Apache, it does not use systemd. Because of this, you must edit the logrotate script supplied with Apache so that it does not use systemctl to reload Apache.

   Remove the following line in the /etc/logrotate.d/httpd file on each node in the cluster.

   /bin/systemctl reload httpd.service > /dev/null 2>/dev/null || true

   Replace the line you removed with the following three lines.

   /usr/bin/test -f /run/httpd.pid >/dev/null 2>/dev/null &&
   /usr/bin/ps -q $(/usr/bin/cat /run/httpd.pid) >/dev/null 2>/dev/null &&
   /usr/sbin/httpd -f /etc/httpd/conf/httpd.conf \
   -c "PidFile /run/httpd.pid" -k graceful > /dev/null 2>/dev/null || true

4. Create a web page for Apache to serve up.

   On one node in the cluster, ensure that the logical volume you created in Configuring an LVM volume with an XFS file system is activated, mount the file system that you created on that logical volume, create the file index.html on that file system, and then unmount the file system.

   # lvchange -ay my_vg/my_lv
   # mount /dev/my_vg/my_lv /var/www/
   # mkdir /var/www/html
   # mkdir /var/www/cgi-bin
   # mkdir /var/www/error
   # restorecon -R /var/www
   # cat <<-END >/var/www/html/index.html
   <html>
   <body>Hello</body>
   </html>
   END
   # umount /var/www

1. An LVM-activate resource named my_lvm that uses the LVM volume group you created in Configuring an LVM volume with an XFS file system.
2. A Filesystem resource named my_fs, that uses the file system device /dev/my_vg/my_lv you created in Configuring an LVM volume with an XFS file system.
3. An IPaddr2 resource, which is a floating IP address for the apachegroup resource group. The IP address must not be one already associated with a physical node. If the IPaddr2 resource’s NIC device is not specified, the floating IP must reside on the same network as one of the node’s statically assigned IP addresses, otherwise the NIC device to assign the floating IP address cannot be properly detected.
4. An apache resource named Website that uses the index.html file and the Apache configuration you defined in Configuring an Apache HTTP server.

Procedure

1. The following command creates the LVM-activate resource my_lvm. Because the resource group apachegroup does not yet exist, this command creates the resource group.

   Note

   Do not configure more than one LVM-activate resource that uses the same LVM volume group in an active/passive HA configuration, as this could cause data corruption. Additionally, do not configure an LVM-activate resource as a clone resource in an active/passive HA configuration.

   [root@z1 ~]# pcs resource create my_lvm ocf:heartbeat:LVM-activate vgname=my_vg vg_access_mode=system_id --group apachegroup

   When you create a resource, the resource is started automatically. You can use the following command to confirm that the resource was created and has started.

   # pcs resource status
    Resource Group: apachegroup
        my_lvm	(ocf::heartbeat:LVM-activate):	Started

   You can manually stop and start an individual resource with the pcs resource disable and pcs resource enable commands.

2. The following commands create the remaining resources for the configuration, adding them to the existing resource group apachegroup.

   [root@z1 ~]# pcs resource create my_fs Filesystem device="/dev/my_vg/my_lv" directory="/var/www" fstype="xfs" --group apachegroup
   
   [root@z1 ~]# pcs resource create VirtualIP IPaddr2 ip=198.51.100.3 cidr_netmask=24 --group apachegroup
   
   [root@z1 ~]# pcs resource create Website apache configfile="/etc/httpd/conf/httpd.conf" statusurl="http://127.0.0.1/server-status" --group apachegroup

3. After creating the resources and the resource group that contains them, you can check the status of the cluster. Note that all four resources are running on the same node.

   [root@z1 ~]# pcs status
   Cluster name: my_cluster
   Last updated: Wed Jul 31 16:38:51 2013
   Last change: Wed Jul 31 16:42:14 2013 via crm_attribute on z1.example.com
   Stack: corosync
   Current DC: z2.example.com (2) - partition with quorum
   Version: 1.1.10-5.el7-9abe687
   2 Nodes configured
   6 Resources configured
   
   Online: [ z1.example.com z2.example.com ]
   
   Full list of resources:
    myapc	(stonith:fence_apc_snmp):	Started z1.example.com
    Resource Group: apachegroup
        my_lvm	(ocf::heartbeat:LVM-activate):	Started z1.example.com
        my_fs	(ocf::heartbeat:Filesystem):	Started z1.example.com
        VirtualIP	(ocf::heartbeat:IPaddr2):	Started z1.example.com
        Website	(ocf::heartbeat:apache):	Started z1.example.com

   Note that if you have not configured a fencing device for your cluster, by default the resources do not start.

4. Once the cluster is up and running, you can point a browser to the IP address you defined as the IPaddr2 resource to view the sample display, consisting of the simple word "Hello".

   Hello

   If you find that the resources you configured are not running, you can run the pcs resource debug-start resource command to test the resource configuration.

Procedure

1. The following command puts node z1.example.com in standby mode.

   [root@z1 ~]# pcs node standby z1.example.com

2. After putting node z1 in standby mode, check the cluster status. Note that the resources should now all be running on z2.

   [root@z1 ~]# pcs status
   Cluster name: my_cluster
   Last updated: Wed Jul 31 17:16:17 2013
   Last change: Wed Jul 31 17:18:34 2013 via crm_attribute on z1.example.com
   Stack: corosync
   Current DC: z2.example.com (2) - partition with quorum
   Version: 1.1.10-5.el7-9abe687
   2 Nodes configured
   6 Resources configured
   
   Node z1.example.com (1): standby
   Online: [ z2.example.com ]
   
   Full list of resources:
   
    myapc	(stonith:fence_apc_snmp):	Started z1.example.com
    Resource Group: apachegroup
        my_lvm	(ocf::heartbeat:LVM-activate):	Started z2.example.com
        my_fs	(ocf::heartbeat:Filesystem):	Started z2.example.com
        VirtualIP	(ocf::heartbeat:IPaddr2):	Started z2.example.com
        Website	(ocf::heartbeat:apache):	Started z2.example.com

   The web site at the defined IP address should still display, without interruption.

3. To remove z1 from standby mode, enter the following command.

   [root@z1 ~]# pcs node unstandby z1.example.com

   Note

   Removing a node from standby mode does not in itself cause the resources to fail back over to that node. This will depend on the resource-stickiness value for the resources. For information on the resource-stickiness meta attribute, see Configuring a resource to prefer its current node.