Tutorial Build and Run a Simple Gameserver (C++)

This tutorial describes how to use the Agones C++ SDK in a simple C++ gameserver.

Objectives

  • Run a simple gameserver
  • Understand how the simple gameserver uses the Agones C++ SDK
  • Build a customized version of the simple gameserver
  • Run your customized simple gameserver

Prerequisites

  1. Docker
  2. Agones installed on GKE
  3. kubectl properly configured
  4. A local copy of the Agones repository
  5. A repository for Docker images, such as Docker Hub or GC Container Registry

To install on GKE, follow the install instructions (if you haven’t already) at Setting up a Google Kubernetes Engine (GKE) cluster. Also complete the “Installing Agones” instructions on the same page.

While not required, you may wish to review the Create a Game Server, Create a Game Server Fleet, and/or Edit a Game Server quickstarts.

1. Run the simple gameserver

First, run the pre-built version of the simple gameserver and take note of the name that was created:

$ kubectl create -f https://raw.githubusercontent.com/googleforgames/agones/release-0.12.0/examples/cpp-simple/gameserver.yaml
$ GAMESERVER_NAME=$(kubectl get gs -o go-template --template '{{range .items}}{{.metadata.name}}{{"\n"}}{{end}}')

The game server sets up the Agones SDK, calls SDK::Ready() to inform Agones that it is ready to serve traffic, prints a message every 10 seconds, and then calls SDK::Shutdown() after a minute to indicate that the gameserver is going to exit.

You can follow along with the lifecycle of the gameserver by running

$ kubectl logs ${GAMESERVER_NAME} cpp-simple -f

which should produce output similar to

C++ Game Server has started!
Getting the instance of the SDK!
Attempting to connect...
...handshake complete.
Setting a label
Starting to watch GameServer updates...
Health ping sent
Setting an annotation
Marking server as ready...
...marked Ready
Getting GameServer details...
GameServer name: cpp-simple-tlgzp
Running for 0 seconds !
GameServer Update:
	name: cpp-simple-tlgzp
	state: Scheduled
GameServer Update:
	name: cpp-simple-tlgzp
	state: RequestReady
GameServer Update:
	name: cpp-simple-tlgzp
	state: RequestReady
GameServer Update:
	name: cpp-simple-tlgzp
	state: Ready
Health ping sent
Health ping sent
Health ping sent
Health ping sent
Health ping sent
Running for 10 seconds !
Health ping sent
...
GameServer Update:
	name: cpp-simple-2mtdc
	state: Ready
Shutting down after 60 seconds...
...marked for Shutdown
Running for 60 seconds !
Health ping sent
GameServer Update:
	name: cpp-simple-2mtdc
	state: Shutdown
GameServer Update:
	name: cpp-simple-2mtdc
	state: Shutdown
Health ping failed
Health ping failed
Health ping failed
Health ping failed
Running for 70 seconds !
Health ping failed
Health ping failed
Health ping failed
Health ping failed
Health ping failed
Running for 80 seconds !
Health ping failed
Health ping failed
Health ping failed
Health ping failed
Health ping failed

If everything goes as expected, the gameserver will exit automatically after about a minute.

In some cases, the gameserver goes into an unhealthy state, in which case it will be restarted indefinitely. If this happens, you can manually remove it by running

$ kubectl delete gs ${GAMESERVER_NAME}

2. Run a fleet of simple gameservers

Next, run a fleet of gameservers

$ kubectl create -f https://raw.githubusercontent.com/googleforgames/agones/release-0.12.0/examples/cpp-simple/fleet.yaml
$ FLEET_NAME=$(kubectl get fleets -o go-template --template '{{range .items}}{{.metadata.name}}{{"\n"}}{{end}}')

You can again inspect the output of an individual gameserver (which will look the same as above), but what is more interesting is to watch the set of all gameservers over time. Each gameserver exits after about a minute, but a fleet is responsible for keeping a sufficient number of gameservers in the Ready state. So as each gameserver exits, it is replaced by a new one. You can see this in action by running

$ watch "kubectl get gameservers"

which should show how gameservers are constantly transitioning from Scheduled to Ready to Shutdown before disappearing.

When you are finished watching the fleet produce new gameservers you should remove the fleet by running

$ kubectl delete fleet ${FLEET_NAME}

3. Build a simple gameserver

Change directories to your local agones/examples/cpp-simple directory. To experiment with the SDK, open up server.cc in your favorite editor and change the interval at which the gameserver calls SDK::Health from 2 seconds to 20 seconds by modifying the line in DoHealth to be

std::this_thread::sleep_for(std::chrono::seconds(20));

Next build a new docker image by running

$ cd examples/cpp-simple
$ REPOSITORY=<your-repository> # e.g. gcr.io/agones-images
$ make build REPOSITORY=${REPOSITORY}

The multi-stage Dockerfile will pull down all of the dependencies needed to build the image. Note that it is normal for this to take several minutes to complete.

Once the container has been built, push it to your repository

$ docker push ${REPOSITORY}/cpp-simple-server:0.6

4. Run the customized gameserver

Now it is time to deploy your newly created gameserver container into your Agones cluster.

First, you need to edit examples/cpp-simple/gameserver.yaml to point to your new image:

containers:
- name: cpp-simple
  image: $(REPOSITORY)/cpp-simple-server:0.6
  imagePullPolicy: Always # add for development

Then, deploy your gameserver

$ kubectl create -f gameserver.yaml
$ GAMESERVER_NAME=$(kubectl get gs -o go-template --template '{{range .items}}{{.metadata.name}}{{"\n"}}{{end}}')

Again, follow along with the lifecycle of the gameserver by running

$ kubectl logs ${GAMESERVER_NAME} cpp-simple -f

which should produce output similar to

C++ Game Server has started!
Getting the instance of the SDK!
Attempting to connect...
...handshake complete.
Setting a label
Health ping sent
Starting to watch GameServer updates...
Setting an annotation
Marking server as ready...
...marked Ready
Getting GameServer details...
GameServer name: cpp-simple-f255n
Running for 0 seconds !
GameServer Update:
	name: cpp-simple-f255n
	state: Scheduled
GameServer Update:
	name: cpp-simple-f255n
	state: Scheduled
GameServer Update:
	name: cpp-simple-f255n
	state: RequestReady
GameServer Update:
	name: cpp-simple-f255n
	state: Ready
Running for 10 seconds !
GameServer Update:
	name: cpp-simple-f255n
	state: Unhealthy
Health ping sent
Running for 20 seconds !
GameServer Update:
	name: cpp-simple-f255n
	state: Unhealthy
Running for 30 seconds !
Health ping sent
Running for 40 seconds !
Running for 50 seconds !
GameServer Update:
	name: cpp-simple-f255n
	state: Unhealthy
Health ping sent
Shutting down after 60 seconds...
...marked for Shutdown
Running for 60 seconds !
Running for 70 seconds !
Health ping sent
Running for 80 seconds !
GameServer Update:
	name: cpp-simple-f255n
	state: Unhealthy
Running for 90 seconds !
Health ping sent

with the slower healthcheck interval, the gameserver gets automatically marked an Unhealthy by Agones.

To finish, clean up the gameserver by manually removing it

$ kubectl delete gs ${GAMESERVER_NAME}