Setting up a two-node ethernet cluster

In this post I would like to share on how to set up a two-node cluster.

First: Configuring the ethernet connection

For every node, we have to configure the network script for the ethernet card, /etc/hosts, /etc/hostname, /etc/resolv.conf, /etc/hosts.allow (and /etc/hosts.deny), and the iptables. The goal is the following:

• Assign private static IPs to every node.
• Assign hostnames to every node.
• Assign a virtual gateway and nameserver
• Allowing communication between the nodes through iptables (if applicable) and hosts.allow.

Let's say we have two nodes and we would like to name them node1 (head node) and node2.

Note: On node1 (chosen as the head node), enp3s0f0 is connected to the internet. So I used enp3s0f1 for the local network.

Sample configuration for node1

$ cat /etc/sysconfig/network-scripts/ifcfg-enp3s0f1

TYPE=Ethernet
BOOTPROTO=none
IPADDR=192.168.1.2 #private IP for node1
NETMASK=255.255.255.0
GATEWAY=192.168.1.1
BROADCAST=192.168.1.255
NETWORK=192.168.1.0
HOSTNAME=node1
DEFROUTE=yes
PEERDNS=yes
PEERROUTES=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=yes
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_PEERDNS=yes
IPV6_PEERROUTES=yes
IPV6_FAILURE_FATAL=no
NAME=enp3s0f1
ONBOOT=yes 
NM_CONTROLLED=no 

Leave /etc/sysconfig/network untouched. 

$ cat /etc/hosts 

192.168.1.1 router 

192.168.1.2 node1 

127.0.0.1 localhost 

192.168.1.3 node2 

$ cat /etc/hostname 

node1 

$ cat /etc/resolv.conf 

nameserver 192.168.1.1 

$ cat /etc/hosts.allow 

ALL+

Configuration for node2 is similar.

The following may be needed at the appropriate line in iptables
-A INPUT -s 192.168.1.0/24 -m state --state NEW,ESTABLISHED -j ACCEPT

The following commands may be required for the changes to take effect:
$ service NetworkManager restart
$ service network restart

Second: Set up passwordless ssh between nodes

For every user, do the following:

# On node1, Generates public and private key pair

$ ssh-keygen -t rsa

#Copy the public key pair to node2. This will also create known_hosts on ~/.ssh

$ scp .ssh/id_rsa.pub node2:~/.ssh/authorized_keys

On node2, do the same (generates key pair and copy the public key to node1).

Easier way

On node1, simply do
$ ssh-copy-id node2

On node2, simpy do
$ ssh-copy-id node1

Third: Set up NFS

Suppose I have /apps directory on node1 that I would like to share with the other node. In this case NFS would be handy.

Important files to configure:

• On NFS server: /etc/exports
• On NFS client: /etc/fstab

On NFS server, to export the directory to be shared

$ cat /etc/exports

/apps    node2(rw,sync,no_root_squash)

On NFS client, to automate the NFS mount on boot

$ cat /etc/fstab

node1:/apps    /apps      nfs    defaults     0 0

Check whether export is successful on the server side by doing the following on the client

$ showmount -e node1

After exporting on the server side, NFS can be mounted on the client side by

$ mount -t nfs node1:/apps /apps

The following command may be required for the changes to take effect:

$ service nfs restart