(FleetCapacityExceededException) when calling the CreateGameSession operation

In this case, you'll want to take a look at how many game sessions you are trying to create/support simultaneously. Even if your fleet is active and healthy, each instance will have a limited capacity for how many sessions it can support. Typically, if you spin up a lot of game sessions at once, or if you have long running sessions, you can fill up your capacity and encounter this exception.

Things to check:

• What size are your instances?
• How many instances do you have?
• How many game sessions do you have?
• Given your instance size/count, can you support your current/expected game sessions?

You can also take a look at the number of processes per instance. This will also affect your game session capacity. You can find more details about fleet processes in these docs: https://docs.aws.amazon.com/gamelift/latest/developerguide/fleets-multiprocess.html