Load Balancing and High Availability Computing

Matt VarnellCameron Adkins

Jeremy Landes

Load Balancing: Overview

Load balancing is the process of distributing a workload evenly throughout a group or cluster of computers to maximize throughput.

This means that workload on individual nodes is reduced, and multiple nodes work together to complete tasks.

Load Balancing: Diagram

High Availability: Overview

High availability clusters allow systems to run continuously even if an error occurs on one ore more nodes.

This works by having multiple redundant nodes in a cluster, each monitoring another with Heartbeat to detect failures, and ready to deploy at any time.

High Availability: Applications

High availability is implemented in almost all cluster systems today.

Most useful in the following systems:› Critical Databases› E-commerce Websites› Network File Sharing

In all of the above systems, any downtime or loss of data is a major problem for business or security.

High Availability: Diagram

Apache: Overview

Apache (or Apache 2.0 for this project) is an open-source, web server software maintained by an open community of web developers.

We chose Apache for ease of use and its readily available packages and support for our heartbeat and high availability on our Unix based system.

The Project

Our goal for this project was to create a load balanced, high availability Apache cluster with the following software:› Ultra Monkey› Heartbeat› Apache 2.0

This was set up on a four-node cluster with all computers running Ubuntu 8.04

Cluster Configuration

Apache node 1: IP address: 190.111.50.201; Apache document root: /var/www Apache node 2: IP address: 190.111.50.202; Apache document root: /var/www Load Balancer node 1: IP address: 190.111.50.203 Load Balancer node 2: IP address: 190.111.50.204 Virtual IP Address: 190.111.50.205 (used for incoming requests)

Apache Configuration

After installing Ubuntu 8.04 on all of the nodes, we had to set up the two Apache nodes:› Installing the proper packages.› Setting up the ethernet configurations in

/etc/init.d/network› Configuring the web page in the proper

directory› Creating and ensuring redundancy

between the two individual Apache server nodes.

Next Step: Load Balance Configuration

Once the Apache nodes were set up, we configured the load balancing nodes with Ultra Monkey.

Most of the issues encountered during configuration occurred during this step.

Ultra Monkey: Background

Our load balancing system uses the Linux based project, Ultra Monkey.

We chose this software as it is freeware, able to run on any size cluster that is needed, and able to run on any OS.

Ultra Monkey also includes the package for Heartbeat protocol, which sends scheduled messages through the system and listens for replies, to check for downed nodes.

If a node is found to be down, due to lack of Heartbeat response, the node assumes the other has failed and takes action.

Load Balance Configuration

The following steps were used to configure load balancing on our nodes:› Installing proper packages› Setting up ethernet configurations in

/etc/init.d/network› Installing and configuring Ultra Monkey› Setting up Heartbeat

Problems Encountered

Some of the major issues encountered during this project involved the Ultra Monkey configuration.

Was mainly trial and error during configuration due to lack of documentation some places and poor or incorrect documentation others.

Did intensive testing and studying to find the correct commands and protocol for setting up the system.

Problems Encountered (cont.)

A problem which stalled our project for a long period of time was the firewall.› Not thought to be an issue at all.› After working for hours trying to find out

why our setup wasn’t connecting between nodes, we disabled.

› Project worked perfectly after this.

Testing the Configuration

In order to test our four-node system, we sequentially cut off machines, both load balancing nodes and Apache nodes in order to see if the system would stay up and online.

The load balancing service was maintained through this process, and the secondary Apache server was able to flawlessly step in when the other was brought down without interrupting service.

Conclusion

It’s easy to see how this project is easily applicable to real world scenarios, as most companies will implement this technology for their cluster systems.

Our setup was for a small cluster, and we didn’t do much optimization; but with the customization options available, load balancing can greatly optimize a system’s capacity.