How Amazon GameLift Servers Realtime servers work
A Realtime server acts as a stateless relay server, where the server relays packets of messages and game data between the game clients that are connected to the game. The Realtime server doesn't evaluate messages, process data, or perform any gameplay logic. Each game client maintains its own view of the game state and provides updates to other players through the relay server. Each game client is responsible for incorporating these updates and reconciling its own game state.
You set up Realtime servers by uploading a Realtime servers script to Amazon GameLift Servers and deploying it to a managed EC2 hosting fleet. The Realtime script is a custom configuration for your game. Amazon GameLift Servers uses the script's instructions to manage the tasks of setting up and running game servers for your players.
The default Realtime script is a set of JavaScript code. You configuration it for use with your game client. Amazon GameLift Servers defines a set of server-side callbacks for Realtime scripts. Implement these callbacks to add event-driven functionality to your server. For example, you can:
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Authenticate a player when a game client tries to connect to the server.
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Validate whether a player can join a group upon request.
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Determine when to deliver messages from a certain player or to a target player, or perform additional processing in response.
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Notify all players when a player leaves a group or disconnects from the server.
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View the content of game session objects or message objects, and use the data.
You can add custom logic for game session management by building it into the Realtime script. You can write code to access server-specific objects, add event-driven logic using callbacks, or add logic based on non-event scenarios. For example, you might add game logic to build a stateful game with a server-authoritative view of the game state.
A key advantage of Amazon GameLift Servers Realtime is the ability to update your scripts at any time. When you update a script, Amazon GameLift Servers distributes the new version to all hosting resources within minutes. After Amazon GameLift Servers deploys the new script, all new game sessions created after that point will use the new script version. (Existing game sessions will continue to use the original version.)
How Realtime clients and servers interact
During a game session, game clients interact by sending messages to the Realtime server through a backend service. The backend service then relays the messages among connected game clients to exchange activity, game state, and relevant game data. If you've added custom game logic to the Realtime script, a Realtime server might implement callbacks to start event-driven responses.
Communication protocol
Realtime servers and connected game clients communicate through two channels: a TCP connection for reliable delivery, and a UDP channel for fast delivery. When creating messages, game clients choose which protocol to use depending on the nature of the message. Message delivery is set to UDP by default. If a UDP channel isn't available, Amazon GameLift Servers sends messages using TCP as a fallback.
Message content
Message content consists of two elements: a required operation code (opCode) and an optional payload. A message's opCode identifies a particular player activity or game event, and the payload provides additional data related to the operation code. Both of these elements are developer-defined. Your game client acts based on the opCodes in the messages that it receives.
Player groups
Amazon GameLift Servers Realtime provides functionality to manage groups of players. By default, Amazon GameLift Servers places all players who connect to a game session into an "all players" group. In addition, developers can set up other groups for their games, and players can be members of multiple groups simultaneously. Group members can send messages and share game data with all players in the group. For example, if your gameplay relies on teams, you can use player groups to enable communication within team members as well as game-wide.