Spot balancing process
Amazon GameLift FleetIQ periodically balances the instances in an Auto Scaling group that has Spot Instances. This process is not active with game server groups that use the ON_DEMAND_ONLY balancing strategy or do not have any active instances.
Spot balancing has two key goals:
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To constantly refresh the group by only using Spot Instance types that are viable for game hosting.
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To use multiple viable instance types (where possible) in order to reduce the impact of unexpected game server interruptions.
Amazon GameLift FleetIQ balances by evaluating the group's instance types and removing instances that are more likely to result in game server interruptions. To avoid terminating instances with active gameplay during balancing, best practice is to turn on game server protection for a game server group that's in production.
The following example illustrates how instances in an Auto Scaling group are affected by Spot balancing.
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Step 1. Through a game server group, the linked Auto Scaling group is set up to launch instances of types m4.large, c4.large, and c5.large with game server protection enabled. The Auto Scaling group has launched a balanced collection consisting of two Spot Instances of each type. Four instances have at least one game server in UTILIZED status (shown with a dashed border), while two instances are not currently supporting gameplay.
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Step 2. Amazon GameLift FleetIQ evaluates the current game hosting viability of all three instance types. The evaluation determines that the c4.large instance type has an unacceptable potential for game server interruption. Amazon GameLift FleetIQ immediately updates the Auto Scaling group configuration to temporarily remove c4.large from the list of instance types, preventing additional c4.large instances from being launched.
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Step 3. Amazon GameLift FleetIQ identifies existing instances of type c4.large and takes actions to remove them from the group. As a first step, all game servers that are running on c4.large instances are flagged as draining. Game servers on draining instances can be claimed only as a last resort if no other game servers are available. In addition, an Auto Scaling group with draining instances is triggered to launch new instances to replace them.
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Step 4. As new viable instances come online, the Auto Scaling group terminates draining instances. This replacement ensures that the group's desired capacity is maintained. The first instance to be terminated is the c4.large instance with no utilized game servers and game server protection turned off. It is replaced with a new c5.large instance.
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Step 5. Draining instances with game server protection continue to run while their game servers are supporting gameplay. When gameplay ends, the remaining c4.large instance is terminated when a new m4.large instance has launched to take its place.
As a result of this process, the Auto Scaling group maintains its desired capacity while the group balances from using three instance types to two. Amazon GameLift FleetIQ continues to evaluate the original list of instance types for game hosting viability. When c4.large is again considered a viable instance type, the Auto Scaling group is updated to include all three instance types. The group naturally balances over time.
