HAProxy and Keepalived Demo

Demo showing how to setup redundant HAProxy servers to load-balance traffic between web servers.

Most of the setup is based on this blog post: HAProxy and Keepalived: Example Configuration

Pre-requisites:

• Vagrant - 1.6.5+
• vagrant-cachier plugin (optional install)
  • vagrant plugin install vagrant-cachier

Setup:

There will be two load-balancer servers running HAProxy and keepalived.

• LB1 will have VRRP priority 101 and is the master load-balancer
• LB2 will have VRRP priority 100 and is the backup load-balancer

Both LBs use round-robin algorithm to route traffic to Web1 and Web2 servers which run Nginx on port 80.

Steps:

Create the 4 VMs:

vagrant up

Test it out:

# Hit web1-box directly
curl http://192.168.33.68

# Hit web2-box directly
curl http://192.168.33.68

# Hit vip
curl http://192.168.33.84

See the HAProxy stats:

LB 1: http://192.168.33.80/stats
LB 2: http://192.168.33.81/stats

In one terminal:

while true; do curl -sI http://192.168.33.84 | head -n 1; sleep 1; done
# ==> HTTP/1.1 200 OK

In a second terminal:

vagrant ssh lb-box1
sudo tcpdump -i eth1

# Look for VRRP advertisements.
# Press CTRL+C

sudo su
watch -n 2 "echo show stat | socat /var/lib/haproxy/stats.sock stdio | grep http,BACKEND"

# Observe the http backend bytes out (column 10)
# It should be going up

In a third terminal:

vagrant ssh lb-box2
sudo tcpdump -i eth1

# Look for VRRP advertisements.
# Press CTRL+C

sudo su
watch -n 2 "echo show stat | socat /var/lib/haproxy/stats.sock stdio | grep http,BACKEND"

# Observe the http backend bytes out (column 10)
# It should be going not be going up

In a fourth terminal:

vagrant halt lb-box1

The curl requests should continue via the vip but be routed to LB2.

Observe the http backend bytes out (column 10) in third terminal (lb-box2) - it should now be going up.

vagrant up lb-box1

The curl requests should continue via the vip but be routed back to LB1.

Learning Resources:

• HAProxy and Keepalived: Example Configuration
• Keepalived and HAProxy in AWS: An Exploratory Guide
• Making HAProxy High Available For MySQL Galera Cluster
• Redundant Load Balancers – HAProxy and Keepalived
• How To Use HAProxy to Set Up HTTP Load Balancing on an Ubuntu VPS
• Virtual Router Redundancy Protocol (VRRP)
• HAProxy Architecture Guide
• keepalived User Guide [PDF]