How to create Floating IP and use it to configure HAProxy

Question

I have recently tried to load balance my application using HAProxy and was able to do it successfully. Later, I have come across a concept called Floating IP, which can be used along with keepalived to make the load balancer highly available. I wasn't able to understand how to create the floating Ip though. How can I create Floating IP and use it to configure HAProxy? Thanks.

Answer 1

Assumptions:

• This works on Ubuntu 14.04
• haproxy-primary IP: 198.51.100.10
• haproxy-secondary IP: 198.51.100.20
• shared IP: 198.51.100.50
• Any DNS rules should point to the shared IP (198.51.100.50)

Steps:

1. Add a firewall rule for keepalived # 224.0.0.18 is the keepalived multicast address
   1. sudo ufw allow in from 198.51.100.20 to 224.0.0.18 # on 198.51.100.10
   2. sudo ufw allow in from 198.51.100.10 to 224.0.0.18 # on 198.51.100.20
2. Allow access to a shared IP address
   1. edit /etc/sysctl.conf
   2. set net.ipv4.ip_nonlocal_bind=1
   3. sudo sysctl -p # reload config change
3. Install keepalived
   1. sudo apt-get install keepalived
4. Configure keepalived on both servers
   1. Edit/create /etc/keepalived/keepalived.conf
   2. See example file below # the priority MUST be different on the primary and secondary servers!
5. Restart keepalived
   1. sudo service keepalived restart
6. Listen on the shared IP address
   1. Edit /etc/haproxy/haproxy.cfg
   2. bind 198.51.100.50:80
7. Restart haproxy (on both haproxy servers)
   1. sudo service haproxy restart
8. Verify proper failover
   1. primary: sudo ip addr show | grep eth0 # should list the shared IP
   2. secondary: sudo ip addr show | grep eth0 # should NOT list the shared IP
   3. primary: sudo service haproxy stop
   4. primary: sudo ip addr show | grep eth0 # should NOT list the shared IP
   5. secondary: sudo ip addr show | grep eth0 # should list the shared IP
   6. primary: sudo service haproxy start
   7. primary: sudo ip addr show | grep eth0 # should list the shared IP
   8. secondary: sudo ip addr show | grep eth0 # should NOT list the shared IP

/etc/keepalived/keepalived.conf

     vrrp_script chk_haproxy {      # Requires keepalived-1.1.13
       script "killall -0 haproxy"  # cheaper than pidof
       interval 2 # check every 2 seconds
       weight 2 # add 2 points of priority if OK
     }
     vrrp_instance VI_1 {
       interface eth0
       state MASTER
       virtual_router_id 51
       priority 101 # 101 on primary, 100 on secondary
       virtual_ipaddress {
         198.51.100.50
       }
       track_script {
         chk_haproxy
       }
     }

Answer 2

The answer from Matt Rice is excellent, but be aware that if you're running SELinux enforcing on Red Hat EL 7, you'll need

sudo setsebool haproxy_connect_any on

...or haproxy will fail to start on the system that does not currently have the virtual ipaddress, with a complaint that it can't bind.