Elastic-Load-Balancing

Update May 2011: Now that AWS Route 53 can be used to allow an ELB to host a domain zone apex, the technique described here is no longer necessary. Cool, but not necessary. Someone really has to implement this. I’ve had this draft sitting around ever since AWS announced support for improved CloudWatch alerts and AutoScaling policies (August 2010), but I haven’t yet turned it into a clear set of commands to follow. If you do, please comment. ...

This is one of the coolest uses of Amazon’s ELB I’ve seen yet. Check out James Elwood’s article. You may know that you can’t serve more than one SSL-enabled domain on a single EC2 instance. Okay, you can but only via a wildcard certificate (limited) or a multi-domain certificate (hard to maintain). So you really can’t do it properly. Serving multiple SSL domains is one of the main use cases behind the popular request to support multiple IP addresses per instance. ...

Help! My ELB isn’t serving files! Whoa! My back-end instances work but not the ELB! Hey! I can’t get the ELB to work! These are among the most common Elastic Load Balancer problems raised on the Amazon EC2 Discussion Forums. Inspired by Eric Hammond’s indispensible article Solving “I can’t connect to my server on Amazon EC2”, here is a helpful guide to debugging these common ELB issues, as well as a utility to perform sanity tests on your own ELBs. ...

If you use AWS’s Elastic Load Balancer to allow your EC2 application to scale, like I do, then you’ll want to know about this gotcha recently reported in the AWS forums. By all appearances, it looks like something that should be fixed by Amazon. Until it is, you can reduce (but not eliminate) your exposure to this problem by keeping a small TTL for your ELB’s DNS CNAME entry. Read on for details. ...

I discovered an interesting feature of Amazon EC2 Elastic Load Balancing today: you can add an EC2 instance to more than one ELB virtual appliance. Below I demonstrate the steps I took to set up two ELBs each containing the same instance, and afterward I explain how this technique can be used to deliver different classes of service. How to Set Up One Instance Belonging to Multiple ELBs I set this up using the standard EC2 API and EC2 ELB command-line tools. First I launched an instance. I used my favorite Alestic image, the Ubuntu 8.04 Hardy Server AMI: ...

Update March 2012: Amazon published their own official guide to ELB’s architecture and building and testing applications that use it. The official material is very consistent with the presentation offered here, more than two and a half years prior. Elastic Load Balancing is a long-anticipated AWS feature that aims to ease the deployment of highly-scalable web applications. Let’s take a look at how it achieves elasticity, based on experience and based on the information available in the AWS forums (mainly this thread). The goal is to understand how to design and test ELB deployments properly. ...