2. Installation
2.1. Install CentOS Stream 8
2.1.1. Boot the Install Image
Download the latest CentOS Stream 8 DVD ISO by navigating to the CentOS Mirrors List [http://isoredirect.centos.org/centos/8-stream/isos/x86_64/], selecting a download mirror which is close to you, and finally selecting the .iso file that has “dvd” in its name. Use the image to boot a virtual machine, or burn it to a DVD or USB drive and boot a physical server from that.
After starting the installation, select your language and keyboard layout at the welcome screen.
CentOS Stream 8 Installation Welcome Screen
2.1.2. Installation Options
At this point, you get a chance to tweak the default installation options.
CentOS Stream 8 Installation Summary Screen
Click on the SOFTWARE SELECTION section (try saying that 10 times quickly). The default environment, Server with GUI, does have add-ons with much of the software we need, but we will change the environment to a Minimal Install here, so that we can see exactly what software is required later, and press Done.
CentOS Stream 8 Software Selection Screen
2.1.3. Configure Network
In the NETWORK & HOSTNAME section:
- Edit Host Name: as desired. For this example, we will use pcmk-1.localdomain and then press Apply.
- Select your network device, press Configure..., and use the Manual method to assign a fixed IP address. For this example, we’ll use 192.168.122.101 under IPv4 Settings (with an appropriate netmask, gateway and DNS server).
- Press Save.
- Flip the switch to turn your network device on, and press Done.
CentOS Stream 8 Network Interface Screen
Important
Do not accept the default network settings. Cluster machines should never obtain an IP address via DHCP, because DHCP’s periodic address renewal will interfere with corosync.
2.1.4. Configure Disk
By default, the installer’s automatic partitioning will use LVM (which allows us to dynamically change the amount of space allocated to a given partition). However, it allocates all free space to the / (aka. root) partition, which cannot be reduced in size later (dynamic increases are fine).
In order to follow the DRBD and GFS2 portions of this guide, we need to reserve space on each machine for a replicated volume.
Enter the INSTALLATION DESTINATION section, ensure the hard drive you want to install to is selected, select Custom to be the Storage Configuration, and press Done.
In the MANUAL PARTITIONING screen that comes next, click the option to create mountpoints automatically. Select the / mountpoint, and reduce the desired capacity by 3GiB or so. Select Modify... by the volume group name, and change the Size policy: to As large as possible, to make the reclaimed space available inside the LVM volume group. We’ll add the additional volume later.
CentOS Stream 8 Manual Partitioning Screen
Press Done, then Accept changes.
2.1.5. Configure Time Synchronization
It is highly recommended to enable NTP on your cluster nodes. Doing so ensures all nodes agree on the current time and makes reading log files significantly easier.
CentOS Stream will enable NTP automatically. If you want to change any time-related settings (such as time zone or NTP server), you can do this in the TIME & DATE section.
2.1.6. Root Password
In order to continue to the next step, a Root Password must be set.
CentOS Stream 8 Root Password Screen
Press Done (depending on the password you chose, you may need to do so twice).
2.1.7. Finish Install
Select Begin Installation. Once it completes, Reboot System as instructed. After the node reboots, you’ll see a login prompt on the console. Login using root and the password you created earlier.
CentOS Stream 8 Console Prompt
Note
From here on, we’re going to be working exclusively from the terminal.
2.2. Configure the OS
2.2.1. Verify Networking
Ensure that the machine has the static IP address you configured earlier.
[root@pcmk-1 ~]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 52:54:00:32:cf:a9 brd ff:ff:ff:ff:ff:ff
inet 192.168.122.101/24 brd 192.168.122.255 scope global noprefixroute enp1s0
valid_lft forever preferred_lft forever
inet6 fe80::c3e1:3ba:959:fa96/64 scope link noprefixroute
valid_lft forever preferred_lft forever
Note
If you ever need to change the node’s IP address from the command line, follow these instructions, replacing ${device} with the name of your network device:
[root@pcmk-1 ~]# vi /etc/sysconfig/network-scripts/ifcfg-${device} # manually edit as desired
[root@pcmk-1 ~]# nmcli dev disconnect ${device}
[root@pcmk-1 ~]# nmcli con reload ${device}
[root@pcmk-1 ~]# nmcli con up ${device}
This makes NetworkManager aware that a change was made on the config file.
Next, ensure that the routes are as expected:
[root@pcmk-1 ~]# ip route
default via 192.168.122.1 dev enp1s0 proto static metric 100
192.168.122.0/24 dev enp1s0 proto kernel scope link src 192.168.122.101 metric 100
If there is no line beginning with default via, then you may need to add a line such as
GATEWAY="192.168.122.1"
to the device configuration using the same process as described above for changing the IP address.
Now, check for connectivity to the outside world. Start small by testing whether we can reach the gateway we configured.
[root@pcmk-1 ~]# ping -c 1 192.168.122.1
PING 192.168.122.1 (192.168.122.1) 56(84) bytes of data.
64 bytes from 192.168.122.1: icmp_seq=1 ttl=64 time=0.492 ms
--- 192.168.122.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.492/0.492/0.492/0.000 ms
Now try something external; choose a location you know should be available.
[root@pcmk-1 ~]# ping -c 1 www.clusterlabs.org
PING mx1.clusterlabs.org (95.217.104.78) 56(84) bytes of data.
64 bytes from mx1.clusterlabs.org (95.217.104.78): icmp_seq=1 ttl=54 time=134 ms
--- mx1.clusterlabs.org ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 133.987/133.987/133.987/0.000 ms
2.2.2. Login Remotely
The console isn’t a very friendly place to work from, so we will now switch to accessing the machine remotely via SSH where we can use copy and paste, etc.
From another host, check whether we can see the new host at all:
[gchin@gchin ~]$ ping -c 1 192.168.122.101
PING 192.168.122.101 (192.168.122.101) 56(84) bytes of data.
64 bytes from 192.168.122.101: icmp_seq=1 ttl=64 time=0.344 ms
--- 192.168.122.101 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.344/0.344/0.344/0.000 ms
Next, login as root via SSH.
[gchin@gchin ~]$ ssh root@192.168.122.101
The authenticity of host '192.168.122.101 (192.168.122.101)' can't be established.
ECDSA key fingerprint is SHA256:NBvcRrPDLIt39Rf0Tz4/f2Rd/FA5wUiDOd9bZ9QWWjo.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '192.168.122.101' (ECDSA) to the list of known hosts.
root@192.168.122.101's password:
Last login: Tue Jan 10 20:46:30 2021
[root@pcmk-1 ~]#
2.2.3. Apply Updates
Apply any package updates released since your installation image was created:
[root@pcmk-1 ~]# yum update
2.2.4. Use Short Node Names
During installation, we filled in the machine’s fully qualified domain name (FQDN), which can be rather long when it appears in cluster logs and status output. See for yourself how the machine identifies itself:
[root@pcmk-1 ~]# uname -n
pcmk-1.localdomain
We can use the hostnamectl tool to strip off the domain name:
[root@pcmk-1 ~]# hostnamectl set-hostname $(uname -n | sed s/\\..*//)
Now, check that the machine is using the correct name:
[root@pcmk-1 ~]# uname -n
pcmk-1
You may want to reboot to ensure all updates take effect.
2.3. Repeat for Second Node
Repeat the Installation steps so far, so that you have two nodes ready to have the cluster software installed.
For the purposes of this document, the additional node is called pcmk-2 with address 192.168.122.102.
2.4. Configure Communication Between Nodes
2.4.1. Configure Host Name Resolution
Confirm that you can communicate between the two new nodes:
[root@pcmk-1 ~]# ping -c 3 192.168.122.102
PING 192.168.122.102 (192.168.122.102) 56(84) bytes of data.
64 bytes from 192.168.122.102: icmp_seq=1 ttl=64 time=1.22 ms
64 bytes from 192.168.122.102: icmp_seq=2 ttl=64 time=0.795 ms
64 bytes from 192.168.122.102: icmp_seq=3 ttl=64 time=0.751 ms
--- 192.168.122.102 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2054ms
rtt min/avg/max/mdev = 0.751/0.923/1.224/0.214 ms
Now we need to make sure we can communicate with the machines by their name. If you have a DNS server, add additional entries for the two machines. Otherwise, you’ll need to add the machines to /etc/hosts on both nodes. Below are the entries for my cluster nodes:
[root@pcmk-1 ~]# grep pcmk /etc/hosts
192.168.122.101 pcmk-1.clusterlabs.org pcmk-1
192.168.122.102 pcmk-2.clusterlabs.org pcmk-2
We can now verify the setup by again using ping:
[root@pcmk-1 ~]# ping -c 3 pcmk-2
PING pcmk-2.clusterlabs.org (192.168.122.102) 56(84) bytes of data.
64 bytes from pcmk-2.clusterlabs.org (192.168.122.102): icmp_seq=1 ttl=64 time=0.295 ms
64 bytes from pcmk-2.clusterlabs.org (192.168.122.102): icmp_seq=2 ttl=64 time=0.616 ms
64 bytes from pcmk-2.clusterlabs.org (192.168.122.102): icmp_seq=3 ttl=64 time=0.809 ms
--- pcmk-2.clusterlabs.org ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2043ms
rtt min/avg/max/mdev = 0.295/0.573/0.809/0.212 ms
2.4.2. Configure SSH
SSH is a convenient and secure way to copy files and perform commands remotely. For the purposes of this guide, we will create a key without a password (using the -N option) so that we can perform remote actions without being prompted.
Warning
Unprotected SSH keys (those without a password) are not recommended for servers exposed to the outside world. We use them here only to simplify the demo.
Create a new key and allow anyone with that key to log in:
Creating and Activating a new SSH Key
[root@pcmk-1 ~]# ssh-keygen -t dsa -f ~/.ssh/id_dsa -N ""
Generating public/private dsa key pair.
Created directory '/root/.ssh'.
Your identification has been saved in /root/.ssh/id_dsa.
Your public key has been saved in /root/.ssh/id_dsa.pub.
The key fingerprint is:
SHA256:ehR595AVLAVpvFgqYXiayds2qx8emkvnHmfQZMTZ4jM root@pcmk-1
The key's randomart image is:
+---[DSA 1024]----+
| . ..+.=+. |
| . +o+ Bo. |
| . *oo+*+o |
| = .*E..o |
| oS..o . |
| .o+. |
| o.*oo |
| . B.* |
| === |
+----[SHA256]-----+
[root@pcmk-1 ~]# cp ~/.ssh/id_dsa.pub ~/.ssh/authorized_keys
Install the key on the other node:
[root@pcmk-1 ~]# scp -r ~/.ssh pcmk-2:
The authenticity of host 'pcmk-2 (192.168.122.102)' can't be established.
ECDSA key fingerprint is SHA256:FQ4sVubTiHdQ6IetbN96fixoTVx/LuQUV8qoyiywnfs.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added 'pcmk-2,192.168.122.102' (ECDSA) to the list of known hosts.
root@pcmk-2's password:
id_dsa 100% 1385 1.6MB/s 00:00
id_dsa.pub 100% 601 1.0MB/s 00:00
authorized_keys 100% 601 1.3MB/s 00:00
known_hosts 100% 184 389.2KB/s 00:00
Test that you can now run commands remotely, without being prompted:
[root@pcmk-1 ~]# ssh pcmk-2 -- uname -n
root@pcmk-2's password:
pcmk-2