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EC2 Spot Instances & Fleet

Links: 101 AWS SAA Index

Actions on a Spot Instance

  • We can hibernate, stop and terminate a spot instance.
  • We CANNOT reboot a spot instance.

Spot Request

  • To get a spot instance we create a Spot Request.
  • The spot request can be one time or persistent.
  • A spot request has the following required parameters defined by us → max price, no of instances, request type, valid from to valid until(can be infinite), launch specification (ami)

The difference between one time and persistent request

  • One Time request → once the request is fulfilled instances are launched and the spot request will go away.
  • Persistent → we want x number of instances from the spot request as long as the spot request is valid (valid from → valid until).
    • If the instances are interrupted because current spot price > max price then the spot request will go back into action and will restart the instances when spot price < max price.
    • If you stop the instances then the instances will not be started automatically.
Cancelling a spot request does not terminate the instances. So it is our responsibility to terminate the running instances.
How to terminate instances in a persistent request?

To terminate all the spot instances in a persistent request you must first cancel the spot request and then terminate the instances. Since in a persistent request if you terminate the spot instances first then the feedback loop will see that x number of instances were needed but there are 0 now so it will start them again.

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Spot Fleets

  • Set of spot instances + optional on demand instances.
  • We define launch pools.
  • Spot fleet stops when maximum capacity is reached or maximum cost defined by us is reached.
  • By default, Spot Fleets are set to maintain target capacity by launching replacement instances after Spot Instances in the fleet are terminated.
  • Strategies to launch spot instances:
    • lowestPrice: short workloads
    • diversified: long workloads
    • capacityOptimised: optimal capacity
Spot fleet allows us to automatically request instances with the lowest price if we use the lowestPrice strategy.
  • The main difference between a spot request and a spot fleet is that in a spot request we know exactly the type of instance we want whereas in spot fleet handles the selection of instance based on the strategy.

Spot Block (Deprecated)

  • Might still be asked in exam.
  • Spot blocks are designed not to be interrupted and will run continuously for the duration you select (1 to 6 hours), independent of the Spot market price.
  • Only in rare situations, spot blocks may be interrupted due to Amazon EC2 capacity needs.

Last updated: 2023-03-24