Is it secure?
Are spot instances risky to use?
Why not just use Reserved Instances?
Reserved instances are a great way to save money on your AWS bill if you can predict your instance type usage levels reasonably well into the future. AutoScalr can still help you save more though, since spot prices are typically significantly below the reserved instance price for the same instance type, and do not require a significant up front commitment like reserved instances do. They are two independent strategies that can help you reduce cost, and you should apply both if you can. As far as working together, AutoScalr will work seamlessly with your reserved instances, using them instead of on demand instances when they are available.
What factors are considered when scaling up or down?
Is my application at risk if the AutoScalr service goes down?
Does AutoScalr support Terraform?
Does AutoScalr support CloudFormation?
Does AutoScalr support Chef / Puppet based deployments?
How does AutoScalr differ from Spot Fleet?
Spot Fleet and AutoScalr both provide diversification across many Spot markets by supporting multiple instance types. Spot Fleet does not provide diversification over a percentage of On-Demand as a guaranteed safety net. Every instance will always be a spot instance of some kind. If your application's availability requirements can tolerate that level of risk, Spot Fleet is a good choice. If giving up a few percentage points of cost savings for an On-Demand safety net sounds appealing, then AutoScalr would be a better choice. A second difference is that Spot Fleet does not natively integrate with the AutoScalingGroup construct widely used in many existing deployments. It does have an AutoScaling capability recently launched, but it must be setup and managed separately, and requires making code changes to the application to get new instances to register with an existing AutoScalingGroup and/or ELB. If you have an existing stack using AutoScalingGroup, you can leverage AutoScalr immediately, Spot Fleet will require some development work. In addition, AutoScalr provides additional cost-saving features that Spot Fleet does not, such as constantly rebalancing instances as prices fluctuate, and maximizing overall compute by never scaling an instance down until it is close to its next hourly billing time. The end result is AutoScalr typically manages clusters at a lower price point than Spot Fleet does.