This guide is 3rd part of Apache High Availability Cluster Configuration series; you can browse other articles using below links:

  • Part 1: Basic Concepts of High Availability Cluster
  • Part 2: Apache High Availability LAB Initial Setup & Configuration
  • Part 3: iSCSI Storage Server & Initiator Configuration
  • Part 4: Configure Apache & Cluster Resources for High Availability

    • Part 3: iSCSI Storage Server & Initiator Configuration

    Storage Server Configuration (iSCSI Target):

    A shared storage solution is an important component of high availability cluster. All cluster members must have access to centralized shared storage, it contains running application data so it can ensure all members of cluster are accessing same data. To provide shared storage solution for cluster we will configure iSCSI shared storage (Storage Area Network) on our storage server. Remember storage server is already up in our network. (storage.broexperts.com : 10.0.0.90)

    • iSCSI protocol is used to provide Storage Area Network (SAN) over Ethernet connection.

    Step 1: Install Required Packages

    Install iSCSI shared storage rpm using following command.

    yum install targetcli -y

    Step 2: Prepare LVMs

    I have one separate disk (/dev/sdb) size of 20GB attached with storage server. I will create two LVMs, one for Fencing and second for Apache Server data directory. Using following command and see command output in screen shot below: 

    fdisk -luc | grep sd

    disk-for-iscsi-storage

    Partitioning 

    [root@storage ~]# fdisk /dev/sdb

    linux-parititioning

    Create physical volume

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

    Creating volume group named cluster_vg

    [root@storage ~]# vgcreate cluster_vg /dev/sdb1
  Volume group "cluster_vg" successfully created

    Create logical volume for fencing device named fence_lvsize 1GB

    [root@storage ~]#  lvcreate -L 1G -n fence_lv cluster_vg
  Logical volume "fence_lv" created.

    Finally create logical volume named data_lv for apache server data directory and assign all free space left on (/dev/sdb)

    [root@storage ~]# lvcreate -l 100%FREE -n data_lv cluster_vg
  Logical volume "data_lv" created.
[root@storage ~]#

    Step 3: Create iSCSI targets

    Before we jump into iSCSI configuration, let’s be comfortable with few terms that i will be using for configuring iSCSI target.

    1. iqn stands for iSCSI Qualified Name, it has mandatory naming format as follows:
      Naming Format: iqn.yyyy.mm.com.domain:optional-string
    2. target: Actually a storage resource made available by iSCSI server to iSCSI clients
    3. LUN: Logical Unit Number, A LUN represents an individually addressable (logical) SCSI device that is part of a physical SCSI device (target).

    As earlier in step 1 we installed targetcli package to configure iSCSI target, now let’s use targetcli command to create storage that will be used shared storage for both nodes in cluster.

    targetcli

    Above command will open command line interface to manage iSCSI targets. Copy and paste below lines in targetcli shell.

    cd /backstores/block
create ap_dir /dev/mapper/cluster_vg-data_lv
create fence_dev /dev/mapper/cluster_vg-fence_lv
cd /iscsi
create iqn.2016-10.com.broexperts:storage
cd iqn.2016-10.com.broexperts:storage/tpg1/acls
create iqn.2016-10.com.broexperts:node1
create iqn.2016-10.com.broexperts:node2
create iqn.2016-10.com.broexperts:node3
cd /iscsi/iqn.2016-10.com.broexperts:storage/tpg1/
set attribute authentication=0
cd /iscsi/iqn.2016-10.com.broexperts:storage/tpg1/luns
create /backstores/block/ap_dir
create /backstores/block/fence_dev
cd /
saveconfig
exit

    Step 4: Start and enable the target service on startup.

    systemctl start target
systemctl enable target

    Step 5: Configure the firewall to allow iSCSI traffic.

    firewall-cmd --permanent --add-port=3260/tcp
firewall-cmd --reload

    Configure Initiators

    After we set all for storage server now it’s time to prepare all nodes for connecting iSCSI targets over the network.

    Step 1: Install Required Package

    yum install iscsi-initiator-utils -y

    Step 2: Discover Exported Targets by Server

    iscsiadm -m discovery -t st -p 10.0.0.90

    Step 3: Edit initiator name file and update initiatorname on both nodes accordingly.

    Node1:

    vi /etc/iscsi/initiatorname.iscsi
InitiatorName=iqn.2016-10.com.broexperts:node1

    Node2:

    vi /etc/iscsi/initiatorname.iscsi
InitiatorName=iqn.2016-10.com.broexperts:node2

    Node3:

    vi /etc/iscsi/initiatorname.iscsi
InitiatorName=iqn.2016-10.com.broexperts:node3

    Step 4: Restart and enable on startup iscsid daemon on all nodes

    systemctl restart iscsid
systemctl enable iscsid

    Step 5: Add iscsi targets on both nodes

    To add iscsi targets on all three nodes enter below command 

    iscsiadm -m node -T iqn.2016-10.com.broexperts:storage -p 10.0.0.90 -l

    iSCSI Shared Storage
    iSCSI Shared Storage