This tutorial will demonstrate how you can use Corosync and Pacemaker with a Floating IP to create a high availability (HA) server infrastructure on DigitalOcean.
Corosync is an open source program that provides cluster membership and messaging capabilities, often referred to as the messaging layer, to client servers. Pacemaker is an open source cluster resource manager (CRM), a system that coordinates resources and services that are managed and made highly available by a cluster. In essence, Corosync enables servers to communicate as a cluster, while Pacemaker provides the ability to control how the cluster behaves.
When completed, the HA setup will consist of two Ubuntu 14.04 servers in an active/passive configuration. This will be accomplished by pointing a Floating IP, which is how your users will access your web service, to point to the primary (active) server unless a failure is detected. In the event that Pacemaker detects that the primary server is unavailable, the secondary (passive) server will automatically run a script that will reassign the Floating IP to itself via the DigitalOcean API. Thus, subsequent network traffic to the Floating IP will be directed to your secondary server, which will act as the active server and process the incoming traffic.
This diagram demonstrates the concept of the described setup:
Note: This tutorial only covers setting up active/passive high availability at the gateway level. That is, it includes the Floating IP, and the load balancer servers—Primary and Secondary. Furthermore, for demonstration purposes, instead of configuring reverse-proxy load balancers on each server, we will simply configure them to respond with their respective hostname and public IP address.
To achieve this goal, we will follow these steps:
- Create 2 Droplets that will receive traffic
- Create Floating IP and assign it to one of the Droplets
- Install and configure Corosync
- Install and configure Pacemaker
- Configure Floating IP Reassignment Cluster Resource
- Test failover
- Configure Nginx Cluster Resource