This repo is meant to be an example of how to easily set up an arbitrary-sized cluster of CentOS 7 machines running Apache's httpd servers with web traffic "load-balanced" by HAProxy on AWS, automated with some shell scripting and Terraform. It's purposefully not using containers, service discovery, auto-scaling, etc, so no scary bleeding-edge DevOps* here.

By default, this demo sets up one t2.micro AWS instance running HAProxy as a "load-balancer", which we'll call instance "A". Note: you'd never want to actually use a micro instance for load-balancing, this is for demo purposes only! The point of "A" is to, as the term implies, balance the load of incoming web traffic for the four t2.micro AWS instances that will be running httpd (i.e. responding to web requests) and answering all queries to the /helloz endpoint with their respective names of "B", "C", "D", and "E". Requests will roundrobin, so refreshing the "A" /helloz endpoint should show an equal amount of responses from "B", "C", "D", and "E". If you're clever, you may figure out why roundrobin may actually not be all that smart in some situations :)

If any of the web instances are turned off they will return to serving traffic once online again (the load-balancer will also resume its job if rebooted). For example, if "C" is experiencing some technical difficulty, and "D" has for some reason had to completely restart, web requests won't be directed at "D" since it's offline. By the way, for this demo, HAProxy's admin interface is exposed at /stats for convenience and testing purposes.

* if further automating SysAdmin-like tasks is the kinda thing you're into, feel free to check out my couchbase-sync-gateway-terraform repo.

Once you're set up, launching entire clusters is as simple as typing ./run.sh, no need for manual SSHing and configuration, and no need to waste time in the AWS dashboard either. Similarly, destroying an entire cluster is as easy as typing terraform destroy -force.

First you need to make sure you have the following command line tools locally installed:

• terraform: infrastructure configuration and launch tool which is provider-agnostic
• awscli: Amazon's unified tool to manage AWS services
• jq: like sed for JSON

If you don't have them and are running OS X (and already have homebrew), running brew install ____ will get any of them on your system.

Clone this repo with git clone https://github.com/PaulCapestany/centos-haproxy-terraform.git and cd to the project. In the main project directory, you'll see the terraform.tfvars-example file, make a copy of it, naming it terraform.tfvars and adding your personal info to it. You should make sure you never check this file into git/Github.

Next, take a look at the variables.tf file. You don't need to change any of them, but if you wanted to change the number of web servers that get deployed, that's where you'd do so. Part of the point of terraform is to keep infrastructure configuration changes under version control (for example, you'd want to make commits after any terraform apply or terraform destroy actions). It might help to read Introduction to Terraform to learn more, but you shouldn't need to in order to run this demo.

Last but not least, execute your deployment with ./run.sh and sit back and relax... you're done! The run.sh shell script basically just runs terraform apply for you, as well as some extra post-launch tasks, such as getting the IPs of the web servers to automatically add them to HAProxy's configuration file, and then restarting the service for you via ssh.

When everything is done launching (which in my testing can take up to 10 minutes), you should see something similar to this:

SUCCESS: Deploy went flawlessly!

Here's how you can find everything:

Instance "B" is at http://52.87.205.58/helloz
Instance "C" is at http://52.201.225.41/helloz
Instance "D" is at http://54.88.147.244/helloz
Instance "E" is at http://52.207.254.31/helloz

Instance "A" (load-balancer) is live at: http://52.23.181.242/helloz
HAProxy Stats can be found at: http://52.23.181.242/stats

Note that /stats is not secured for the purposes of this demo, and allows anyone to easily take backends down/up/etc via the admin panel. You probably wouldn't want to do this otherwise, but it's a quick and straightforward way to test whether your HAProxy load-balancer is really working properly.

IMPORTANT: to completely destroy the cluster, run terraform destroy -force within the project directory, otherwise you might get an unexpectedly more expensive AWS bill.