Creating a Realtime script - Amazon GameLift

Creating a Realtime script

To use Realtime Servers for your game, you need to provide a script (in the form of some JavaScript code) to configure and optionally customize a fleet of Realtime Servers. This topic covers the key steps in creating a Realtime script. Once the script is ready, upload it to the Amazon GameLift service and use it to create a fleet (see Upload a Realtime Servers script to Amazon GameLift).

To prepare a script for use with Realtime Servers, add the following functionality to your Realtime script.

Manage game session life-cycle (required)

At a minimum, a Realtime script must include the Init() function, which prepares the Realtime server to start a game session. It is also highly recommended that you also provide a way to terminate game sessions, to ensure that new game sessions can continue to be started on your fleet.

The Init() callback function, when called, is passed a Realtime session object, which contains an interface for the Realtime server. See Realtime Servers interface for more details on this interface.

To gracefully end a game session, the script must also call the Realtime server's session.processEnding function. This requires some mechanism to determine when to end a session. The script example code illustrates a simple mechanism that checks for player connections and triggers game session termination when no players have been connected to the session for a specified length of time.

Realtime Servers with the most basic configuration--server process initialization and termination--essentially act as stateless relay servers. The Realtime server relays messages and game data between game clients that are connected to the game, but takes no independent action to process data or perform logic. You can optionally add game logic, triggered by game events or other mechanisms, as needed for your game.

Add server-side game logic (optional)

You can optionally add game logic to your Realtime script. For example, you might do any or all of the following. The script example code provides illustration. See Amazon GameLift Realtime Servers script reference.

Realtime Servers script example

This example illustrates a basic script needed to deploy Realtime Servers plus some custom logic. It contains the required Init() function, and uses a timer mechanism to trigger game session termination based on length of time with no player connections. It also includes some hooks for custom logic, including some callback implementations.

// Example Realtime Server Script 'use strict'; // Example override configuration const configuration = { pingIntervalTime: 30000, maxPlayers: 32 }; // Timing mechanism used to trigger end of game session. Defines how long, in milliseconds, between each tick in the example tick loop const tickTime = 1000; // Defines how to long to wait in Seconds before beginning early termination check in the example tick loop const minimumElapsedTime = 120; var session; // The Realtime server session object var logger; // Log at appropriate level via .info(), .warn(), .error(), .debug() var startTime; // Records the time the process started var activePlayers = 0; // Records the number of connected players var onProcessStartedCalled = false; // Record if onProcessStarted has been called // Example custom op codes for user-defined messages // Any positive op code number can be defined here. These should match your client code. const OP_CODE_CUSTOM_OP1 = 111; const OP_CODE_CUSTOM_OP1_REPLY = 112; const OP_CODE_PLAYER_ACCEPTED = 113; const OP_CODE_DISCONNECT_NOTIFICATION = 114; // Example groups for user-defined groups // Any positive group number can be defined here. These should match your client code. // When referring to user-defined groups, "-1" represents all groups, "0" is reserved. const RED_TEAM_GROUP = 1; const BLUE_TEAM_GROUP = 2; // Called when game server is initialized, passed server's object of current session function init(rtSession) { session = rtSession; logger = session.getLogger(); } // On Process Started is called when the process has begun and we need to perform any // bootstrapping. This is where the developer should insert any code to prepare // the process to be able to host a game session, for example load some settings or set state // // Return true if the process has been appropriately prepared and it is okay to invoke the // GameLift ProcessReady() call. function onProcessStarted(args) { onProcessStartedCalled = true;"Starting process with args: " + args);"Ready to host games..."); return true; } // Called when a new game session is started on the process function onStartGameSession(gameSession) { // Complete any game session set-up // Set up an example tick loop to perform server initiated actions startTime = getTimeInS(); tickLoop(); } // Handle process termination if the process is being terminated by GameLift // You do not need to call ProcessEnding here function onProcessTerminate() { // Perform any clean up } // Return true if the process is healthy function onHealthCheck() { return true; } // On Player Connect is called when a player has passed initial validation // Return true if player should connect, false to reject function onPlayerConnect(connectMsg) { // Perform any validation needed for connectMsg.payload, connectMsg.peerId return true; } // Called when a Player is accepted into the game function onPlayerAccepted(player) { // This player was accepted -- let's send them a message const msg = session.newTextGameMessage(OP_CODE_PLAYER_ACCEPTED, player.peerId, "Peer " + player.peerId + " accepted"); session.sendReliableMessage(msg, player.peerId); activePlayers++; } // On Player Disconnect is called when a player has left or been forcibly terminated // Is only called for players that actually connected to the server and not those rejected by validation // This is called before the player is removed from the player list function onPlayerDisconnect(peerId) { // send a message to each remaining player letting them know about the disconnect const outMessage = session.newTextGameMessage(OP_CODE_DISCONNECT_NOTIFICATION, session.getServerId(), "Peer " + peerId + " disconnected"); session.getPlayers().forEach((player, playerId) => { if (playerId != peerId) { session.sendReliableMessage(outMessage, playerId); } }); activePlayers--; } // Handle a message to the server function onMessage(gameMessage) { switch (gameMessage.opCode) { case OP_CODE_CUSTOM_OP1: { // do operation 1 with gameMessage.payload for example sendToGroup const outMessage = session.newTextGameMessage(OP_CODE_CUSTOM_OP1_REPLY, session.getServerId(), gameMessage.payload); session.sendGroupMessage(outMessage, RED_TEAM_GROUP); break; } } } // Return true if the send should be allowed function onSendToPlayer(gameMessage) { // This example rejects any payloads containing "Reject" return (!gameMessage.getPayloadAsText().includes("Reject")); } // Return true if the send to group should be allowed // Use gameMessage.getPayloadAsText() to get the message contents function onSendToGroup(gameMessage) { return true; } // Return true if the player is allowed to join the group function onPlayerJoinGroup(groupId, peerId) { return true; } // Return true if the player is allowed to leave the group function onPlayerLeaveGroup(groupId, peerId) { return true; } // A simple tick loop example // Checks to see if a minimum amount of time has passed before seeing if the game has ended async function tickLoop() { const elapsedTime = getTimeInS() - startTime;"Tick... " + elapsedTime + " activePlayers: " + activePlayers); // In Tick loop - see if all players have left early after a minimum period of time has passed // Call processEnding() to terminate the process and quit if ( (activePlayers == 0) && (elapsedTime > minimumElapsedTime)) {"All players disconnected. Ending game"); const outcome = await session.processEnding();"Completed process ending with: " + outcome); process.exit(0); } else { setTimeout(tickLoop, tickTime); } } // Calculates the current time in seconds function getTimeInS() { return Math.round(new Date().getTime()/1000); } exports.ssExports = { configuration: configuration, init: init, onProcessStarted: onProcessStarted, onMessage: onMessage, onPlayerConnect: onPlayerConnect, onPlayerAccepted: onPlayerAccepted, onPlayerDisconnect: onPlayerDisconnect, onSendToPlayer: onSendToPlayer, onSendToGroup: onSendToGroup, onPlayerJoinGroup: onPlayerJoinGroup, onPlayerLeaveGroup: onPlayerLeaveGroup, onStartGameSession: onStartGameSession, onProcessTerminate: onProcessTerminate, onHealthCheck: onHealthCheck };