How can I configure an automatic timeout for an Elastic Load Balancer?

Question

Does anyone know of a way to make Amazon's Elastic Load Balancers timeout if an HTTP response has not been received from upstream in a set timeframe?

Occasionally Amazon's Elastic Beanstalk will fail an update and any requests to the specified resource (running Nginx + Node if tht's any use) will hang any request pages whilst the resource attempts to load.

I'd like to keep the request timeout under 2s, and if the upstream server has no response by then, to automatically fail over to a default 503 response.

Is this possible with ELB?

Cheers

Answer 1

You can Configure Health Check Settings for Elastic Load Balancing to achieve this:

Elastic Load Balancing routinely checks the health of each registered Amazon EC2 instance based on the configurations that you specify. If Elastic Load Balancing finds an unhealthy instance, it stops sending traffic to the instance and reroutes traffic to healthy instances. For more information on configuring health check, see Health Check.

For example, you simply need to specify an appropriate Ping Path for the HTTP health check, a Response Timeout of 2 seconds and an UnhealthyThreshold of 1 to approximate your specification.

• See my answer to What does the Amazon ELB automatic health check do and what does it expect? for more details on how the ELB health check system work.

Answer 2

TLDR - Set your timeout in Nginx.

Let's see if we can walkthrough the issues.

Problem: The client should be presented with something quickly. It's okay if it's a 500 page. However, the ELB currently waits 60 seconds until giving up (https://forums.aws.amazon.com/thread.jspa?messageID=382182) which means it takes a minute before the user is shown anything.

Solutions:

1. Change the timeout of the ELB Looks like AWS support will help increase the timeout (https://forums.aws.amazon.com/thread.jspa?messageID=382182) so I imagine that you'll be able to ask for the reverse. Thus, we can see that it's not user/api tunable and requires you to interact with support. This takes a bit of lead time and more importantly, seems like an odd dial to tune when future developers working on this project will be surprised by such a short timeout.

2. Change the timeout of the nginx server This seems like the right level of change. You can use proxy_read_timeout (http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_read_timeout) to do what you're looking for. Tune it to something small (and in particular, you can set it for a particular location if you would like).

3. Change the way the request happens. It may be beneficial to change how your client code works. You could imagine shipping a really simple html/js page that 1. pings to see if the job is done and 2. keeps the user updated on the progress. This takes a bit more work then just throwing the 500 page.

Answer 3

Recently, AWS added a way to configure timeouts for ELB. See this blog post:

http://aws.amazon.com/blogs/aws/elb-idle-timeout-control/