Auto Scaling - Across regions?

Question

I hope you can provide a quick response to my question.

Is it possible to create auto scaling group which spans across regions ? Consider this scenario - Lets say all the availability zones in west are unavailabe. Can we configure auto scaling so that if the instance in US.West are down, create an instance in east zone ?

I dont think it is possible, because we need to specify the region for AWS_AUTO_SCALING_URL while using Command line scripts, which restricts the creation of launch configs, auto scaling group within that region only.

So we can only hope all the AZ's in that region are not down or move to VPC is that right ?

Answer 1

Elastic load balancing and Elastic IP are both region specific, I would assume that auto scaling is region specific and only between the availability zones in that region. The white paper on building fault tolerant applications doesn't explicitly state that you could auto-scale across regions but it does say that you can across zones.

"Auto Scaling can work across multiple Availability Zones in an AWS Region, making it easier to automate increasing and decreasing of capacity."

I would believe if they supported multi-region, they would explicitly say so.

Thinking about this further, I'm not so sure it's even a good idea to auto-scale across regions. Auto-scale is more geared for a specific tier of your application.

For example, if a region was to go down, you would not want some of your web servers to use services across a slow link to another region (potentially) across the country.

Instead you would want route 53 to route the traffic to an autonomous stack running it's own auto-scaled layers in a separate region.

see this hosting chart everything from ELB down is region specific.

Answer 2

An Auto Scaling group can contain EC2 instances from multiple Availability Zones within the same region. However, an Auto Scaling group can't contain EC2 instances from multiple regions.

Read Note in this AWS Document