What is the advantage of using Spot Fleet Autoscaling instead of AutoScaling Groups with a Spot Price?

Question

Recently Amazon AWS released Auto Scaling for Spot Fleets (https://aws.amazon.com/blogs/aws/new-auto-scaling-for-ec2-spot-fleets/). Auto Scaling groups already allowed you to set a Spot Price to get Spot Instances at a discount instead of Reserved Instances.

As far as I could see Spot Fleets allow you to define the fleet capacity in terms of vCPU, mixing different instance types to achieve this. I don't think this can be done using Auto Scaling as far as I know.

My use case is pretty simple: use Spot Fleets (or Auto Scaling with Spot instances) to increase the capacity of my cluster at a reduced price while keeping the minimum required Reserved Instances just in case. I could duplicate my ASG, set a spot price and I'd be done, but apparently this functionality now also exists as part of Spot Fleets.

What is the advantage of one over the other? Are there any major reasons to switch?

Answer 1

I might've found a valid reason to keep using Auto Scaling Groups with Spot Instances: you can attach those to a load balancer / target group, while spot fleets can't do that as of now.

Not that it matters too much for my use case any way as my cluster is an ECS cluster and instances will get registered in target groups automatically when launching containers, but it's good to know anyway.

Edit: Apparently Spot Fleets do not support CreationPolicies either, so you're either left to use ASGs or have some fun with WaitConditions if that is needed.

Answer 2

The major advantage of Spot Fleet is that it re-balances instances across availability zones if an AZ is experiencing a price spike. In contrast, ASG would leave you with fewer running instances than you requested.

This, along with the ability to balance across instance types and not just availability zones, makes Spot Fleets much more reliable for maintaining a target capacity than ASG. They come at an opportune time, since spot prices are seeing ever greater volatility.

That said, Spot Fleet currently is missing a lot of features afforded by ASG, as Ruben mentioned.