Centos 6, Corosync and Pacemaker for a simple Active/Passive cluster

Just playing with Corosync so I thought I would include a simple howto. For examples sake, we will setup an OpenVPN server with a fail-over.

I set this up on 2 KVM guests using the default network configuration. In the examples I will use the ip addresses of my guests, change them to match your setup.

host1: 192.168.122.20
host2: 192.168.122.21
Clustered IP:  192.168.122.23

1. Prerequisites

Software Packages

You will need the EPEL repository setup.

# yum install http://mirror.iprimus.com.au/epel/6/i386/epel-release-6-7.noarch.rpm

Install the required packages on both machines.

# yum install corosync pacemaker openvpn

You should set corosync to run on startup. But do not set openvpn to run. Pacemaker will start OpenVPN when required.

# chkconfig corosync on

Firewall

If your lazy you can disable the firewall but I would suggest opening the required ports. For corosync, use the following filtering. Port 5405 is used to receive multicast traffic.

iptables -I INPUT -p udp -m state --state NEW -m multiport --dports 5404,5405 -j ACCEPT

If you are installing OpenVPN allow udp traffic on 1194.

2. Configure Corsync

On our first host.

Setup the corosync authkey

# corosync-keygen
Press keys on your keyboard to generate entropy.
Press keys on your keyboard to generate entropy (bits = 160).

Note. If you are remotely logged in, no amount of key bashing will work. You need to be connected to console for key-smashing to result in entropy. One novel suggestion for generating IO I found on a forum, was to download the latest kernel source, untar and then run a find over the resulting directory tree.

Copy the file “/etc/corosync/authkey” to the other host. Set the permission to “0400”.

corosync.conf

We will use the example config included. Copy this file and edit it.

cp /etc/corosync/corosync.conf.example /etc/corosync/corosync.conf

We need to set bindnetaddr to our local subnet:

bindnetaddr: 192.168.122.0

And we need corosync to start pacemaker. Add the following to the end of the file

service {
	# Load the Pacemaker Cluster Resource Manager
	name: pacemaker
	ver: 0
}

Start Corosync

# service corosync start

Once corosync has started successfully on the first host:

# ssh 192.168.122.21 -- service corosync start

Run “crm_mon” you should see that corosync is running on 2 nodes.

Setting up Active/Passive Cluster

Disable Stonith:

crm configure property stonith-enabled=false

Add a cluster IP

crm configure primitive ClusterIP ocf:heartbeat:IPaddr2 params ip=172.25.3.20 cidr_netmask=21 op monitor interval=30s

Disable Failback (there is no need to failback in this case)

crm configure rsc_defaults resource-stickiness=100

With 2 nodes we cannot attain a quorum

crm configure property no-quorum-policy=ignore

Print the current config

crm configure show

You should now be able to ping you new cluster IP address 192.168.122.23. This ip address should remain available if you turn off corosync on the first host, or even shut it down.

Adding a service

Configure OpenVPN

This is not a post about setting up openvpn. I wrote about that previously, though the post is specific to Debian. I have included my config file though.

Once configured copy the entire directory structure “/etc/openvppn” to the second host.

$ cat /etc/openvpn/openvpn.conf

# This is the clustered IP
local 192.168.122.23

dev tun
proto udp 
port 1194 

ca /etc/openvpn/easy-rsa/2.0/keys/ca.crt
cert /etc/openvpn/easy-rsa/2.0/keys/centosvm.crt
key /etc/openvpn/easy-rsa/2.0/keys/centosvm.key
dh /etc/openvpn/easy-rsa/2.0/keys/dh1024.pem

user openvpn
group openvpn
## You can make this any private subnet you like
server 192.168.123.0 255.255.255.0

persist-key
persist-tun

client-to-client

## make this connection the default gateway for network traffic
push "redirect-gateway def1"
push "dhcp-option DNS 192.168.122.1"
    
log-append /var/log/openvpn

plugin /usr/lib64/openvpn/plugin/lib/openvpn-auth-pam.so system-auth
client-cert-not-required
username-as-common-name

Add Pacemaker rules

# crm configure primitive p_openvpn ocf:heartbeat:anything params binfile="/usr/sbin/openvpn" cmdline_options="--writepid /var/run/openvpn.pid --config /etc/openvpn/openvpn.conf --cd /etc/openvpn --daemon" pidfile="/var/run/openvpn.pid" op start timeout="20" op stop timeout="30" op monitor interval="20"
# crm configure commit

If all of this has worked you should now have an Active/Passive OpenVPN cluster.

3 thoughts on “Centos 6, Corosync and Pacemaker for a simple Active/Passive cluster”

  1. Awesome! Great thanks for this guide!
    The only comment I have – in section “Add a cluster IP”, obviously the Cluster ip should be used, which is in your case “192.168.122.23”, not “192.168.122.20”.

  2. What is keeping the vpn and cluster ip running on the same node. Or from running on different nodes.
    I think you need a ‘group cluster p_openvpn ClusterIP meta target-role=”Started”‘

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