High Density GameServers

Depending on the setup and resource requirements of your game server process, sometimes it can be a more economical use of resources to run multiple concurrent game sessions from within a single GameServer instance.

The tradeoff here is that this requires more management on behalf of the integrated game server process and external systems, since it works around the common Kubernetes and/or Agones container lifecycle.

Utilising the new allocation gameServerState filter as well as the existing ability to edit the GameServer labels at both allocation time, and from within the game server process, via the SDK, means Agones is able to atomically remove a GameServer from the list of potentially allocatable GameServers at allocation time, and then return it back into the pool of allocatable GameServers if and when the game server process deems that is has room to host another game session.

Example GameServerAllocation

The below Allocation will first attempt to find a GameServer from the Fleet simple-udp that is already Allocated and also has the label agones.dev/sdk-gs-session-ready with the value of true.

The above condition indicates that the matching game server process behind the matched GameServer record is able to accept another game session at this time.

If an Allocated GameServer does not exist with the desired labels, then use the next selector to allocate a Ready GameServer from the simple-udp Fleet.

Whichever condition is met, once allocation is made against a GameServer, its label of agones.dev/sdk-gs-session-ready will be set to the value of false and it will no longer match the first selector, thereby removing it from any future allocations with the below schema.

It will then be up to the game server process to decide on if and when it is appropriate to set the agones.dev/sdk-gs-session-ready value back to true, thereby indicating that it can accept another concurrent gameplay session.

apiVersion: "allocation.agones.dev/v1"
kind: GameServerAllocation
spec:
  selectors:
    - matchLabels:
        agones.dev/fleet: simple-udp
        agones.dev/sdk-gs-session-ready: "true" # this is important
      gameServerState: Allocated # new state filter: allocate from Allocated servers
    - matchLabels:
        agones.dev/fleet: simple-udp
      gameServerState: Ready # Allocate out of the Ready Pool (which would be default, so backward compatible)
  metadata:
    labels:
      agones.dev/sdk-gs-session-ready: "false" # this removes it from the pool

Consistency

Agones, and Kubernetes itself are built as eventually consistent, self-healing systems. To that end, it is worth noting that there may be minor delays between each of the operations in the above flow. For example, depending on the cluster load, it may take up to a second for an SDK driven label change on a GameServer record to be visible to the Agones allocation system. We recommend building your integrations with Agones with this in mind.

Next Steps

• View the details about using the SDK to set labels on the GameServer.
• Check all the options available on GameServerAllocation.