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health_checking.md

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GameServer Health Checking

Health checking exists to track the overall healthy state of the GameServer, such that action can be taken when a something goes wrong or a GameServer drops into an Unhealthy state

Disabling Health Checking

By default, health checking is enabled, but it can be turned off by setting the health > disabled property to true

SDK API

The Health() function on the SDK object needs to be called at an interval less than the health > periodSeconds threshold time to be considered before it will be considered a failure.

The health check will also need to have not been called a consecutive number of times (health > failureTheshold), giving it a chance to heal if it there is an issue.

Health Failure Strategy

The following is the process for what happens to a GameServer when it is unhealthy.

  1. If any of the GameServer container fails health checking, or exits before the GameServer moves to Ready then, it is restart as per the restartPolicy (which defaults to "Always")
  2. If the GameServer container fails healthy checking after the Ready state, then it doesn't restart, but moves the GameServer to an Unhealthy state.
  3. If the GameServer container exits while in Ready state, it will restart as per the restartPolicy (which defaults to "Always", since RestartPolicy is a Pod wide setting), but will immediately move to an Unhealthy state.
  4. If the SDK sidecar fails, then it wiil restarted, assuming the RestartPolicy is Always/OnFailure.

Reference

  # Health checking for the running game server
  health:
    # Disable health checking. defaults to false, but can be set to true
    disabled: false
    # Number of seconds after the container has started before health check is initiated. Defaults to 5 seconds
    initialDelaySeconds: 5
    # If the `Health()` function doesn't get called at least once every period (seconds), then
    # the game server is not healthy. Defaults to 5
    periodSeconds: 5
    # Minimum consecutive failures for the health probe to be considered failed after having succeeded.
    # Defaults to 3. Minimum value is 1
    failureThreshold: 3

See the full GameServer example for more details

Example

C++

For a configuration that requires a health ping every 5 seconds, the example below sends a request every 2 seconds to be sure that the GameServer is under the threshold.

void doHealth(agones::SDK *sdk) {
    while (true) {
        if (!sdk->Health()) {
            std::cout << "Health ping failed" << std::endl;
        } else {
            std::cout << "Health ping sent" << std::endl;
        }
        std::this_thread::sleep_for(std::chrono::seconds(2));
    }
}

int main() {
    agones::SDK *sdk = new agones::SDK();
    bool connected = sdk->Connect();
    if (!connected) {
        return -1;
    }
    std::thread health (doHealth, sdk);

    // ...  run the game server code

}

Full Game Server

Also look in the examples directory.