EC2 Spot Instances & Fleet
Links: 101 AWS SAA Index
- 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 →
no of instances,
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 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.
- 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.
- Spot fleet allows us to automatically request instances with the lowest price.
- 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.
- 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: 2022-05-02