How do you put up a maintenance page for AWS when your instances are behind an ELB?

Question

How do you put up a maintenance page in AWS when you want to deploy new versions of your application behind an ELB? We want to have the ELB route traffic to the maintenance instance while the new auto-scaled instances are coming up, and only "flip over" to the new instances once they're fully up. We use auto-scaling to bring existing instances down and new instances, which have the new code, up.

The scenario we're trying to avoid is having the ELB serve both traffic to new EC2 instances while also serving up the maintenance page. Since we dont have sticky sessions enabled, we want to prevent the user from being flipped back and forth between the maintenance-mode page and the application deployed in an EC2 instance. We also can't just scale up (say from 2 to 4 instances and then back to 2) to introduce the new instances because the code changes might involve database changes which would be breaking changes for the old code.

Answer 1

I realise this is an old question but after facing the same problem today (December 2018), it looks like there is another way to solve this problem.

Earlier this year, AWS introduced support for redirects and fixed responses to Application Load Balancers. In a nutshell:

• Locate your ELB in the console.
• View the rules for the appropriate listener.
• Add a fixed 503 response rule for your application's host name.
• Optionally provide a text/plain or text/html response (i.e. your maintenance page HTML).
• Save changes.

Once the rule propagates to the ELB (took ~30 seconds for me), when you try to visit your host in your browser, you'll be shown the 503 maintenance page.

When your deployment completes, simply remove the rule you added.

Answer 2

The simplest way on AWS is to use Route 53, their DNS service.

You can use the feature of Weighted Round Robin.

"You can use WRR to bring servers into production, perform A/B testing, or balance your traffic across regions or data centers of varying sizes."

More information in AWS documentations on this feature

EDIT: Route 53 recently added a new feature that allows DNS Failover to S3. Check their documentation for more details: http://docs.aws.amazon.com/Route53/latest/DeveloperGuide/dns-failover.html