Quickstart: Create a Fleet Autoscaler

Prerequisites

It is assumed that you have followed the instructions to Create a Game Server Fleet and you have a running fleet of game servers.

Objectives

• Create a Fleet Autoscaler in Kubernetes using Agones custom resource.
• Watch the Fleet scale up when allocating GameServers
• Watch the Fleet scale down when shutting down allocated GameServers
• Edit the autoscaler specification to apply live changes

1. Create a Fleet Autoscaler

Let’s create a Fleet Autoscaler using the following command :

kubectl apply -f https://raw.githubusercontent.com/googleforgames/agones/release-1.49.0/examples/simple-game-server/fleetautoscaler.yaml

You should see a successful output similar to this :

This has created a FleetAutoscaler record inside Kubernetes.

2. See the autoscaler status.

kubectl describe fleetautoscaler simple-game-server-autoscaler

It should look something like this:

You can see the status (able to scale, not limited), the last time the fleet was scaled (nil for never) and the current and desired fleet size.

The autoscaler works by changing the desired size, and the fleet creates/deletes game server instances to achieve that number. The convergence is achieved in time, which is usually measured in seconds.

3. Allocate a Game Server from the Fleet

If you’re interested in more details for game server allocation, you should consult the Create a Game Server Fleet page. In here we are only interested in triggering allocations to see the autoscaler in action.

kubectl create -f https://raw.githubusercontent.com/googleforgames/agones/release-1.49.0/examples/simple-game-server/gameserverallocation.yaml -o yaml

You should get in return the allocated game server details, which should end with something like:

Note the address and port, you might need them later to connect to the server.

4. See the autoscaler in action

Now let’s wait a few seconds to allow the autoscaler to detect the change in the fleet and check again its status

kubectl describe fleetautoscaler simple-game-server-autoscaler

The last part should look something like this:

You can see that the fleet size has increased, the autoscaler having compensated for the allocated instance. Last Scale Time has been updated, and a scaling event has been logged.

Double-check the actual number of game server instances and status by running

kubectl get gs

This will get you a list of all the current GameServers and their Status > State.

5. Shut the allocated instance down

Since we’ve only got one allocation, we’ll just grab the details of the IP and port of the only allocated GameServer:

kubectl get gameservers | grep Allocated | awk '{print $3":"$4 }'

This should output your Game Server IP address and port. (eg 10.130.65.208:7936)

You can now communicate with the GameServer:

You can finally type EXIT which tells the SDK to run the Shutdown command, and therefore shuts down the GameServer.

6. See the fleet scaling down

Now let’s wait a few seconds to allow the autoscaler to detect the change in the fleet and check again its status

kubectl describe fleetautoscaler simple-game-server-autoscaler

It should look something like this:

You can see that the fleet size has decreased, the autoscaler adjusting to game server instance being de-allocated, the Last Scale Time and the events have been updated. Note that simple-game-server game server instance you just closed earlier might stay a bit in ‘Unhealthy’ state (and its pod in ‘Terminating’ until it gets removed.

Double-check the actual number of game server instances and status by running

kubectl get gs

This will get you a list of all the current GameServers and their Status > State.

7. Change autoscaling parameters

We can also change the configuration of the FleetAutoscaler of the running Fleet, and have the changes applied live, without interruptions of service.

Run kubectl edit fleetautoscaler simple-game-server-autoscaler and set the bufferSize field to 5.

Let’s look at the list of game servers again. Run watch kubectl get gs until you can see that are 5 ready server instances:

Next Steps

Read the advanced Scheduling and Autoscaling guide, for more details on autoscaling.

If you want to use your own GameServer container make sure you have properly integrated the Agones SDK.