Its mentioned that spot instances can be used for urgent capacity. My question is if there is an urgency then how spot can help? Because the user has to wait for that specific price spot before the instances can be allocated.
The lecture states spot instances are not good candidates for persistent workloads, critical jobs and databases, so I wouldn’t use spot instances for urgent tasks.
You are correct in that there may not even be the type or quantity of spot instances you want at a price you are willing to pay. Spot Fleets can help you get a pool of instances and even mix on demand instances with spot instances. You can also set strategies to look for available instance types and AZs.
In addition you can use Spot Blocking to delay termination of running instances if the spot prices goes above your bid price.
It could refer to using a fleet of Spot Instances for web applications and servers during peak traffic for lower costs. Your website could be experiencing a surge of traffic and you need instances quickly, but want low cost. Source: https://aws.amazon.com/ec2/spot/getting-started/#WebApplicationsandServicesonSpotInstances