multiplayer_lambda_function.py

import json
import boto3

multiplayerFleetID = "fleet-00000a00-0000-000a-0a00-0a0aaaaaa00a"
maximumPlayersBySession = 2

def lambda_handler(event, context):
    client = boto3.client('gamelift')

    try:
        # Find any sessions that have available players
        response = client.search_game_sessions(
            FleetId=multiplayerFleetID,
            FilterExpression="hasAvailablePlayerSessions=true"
        )
        game_sessions = response["GameSessions"]

        # If there are no sessions, then we need to create a game session
        if len(game_sessions) == 0:
            # No game session detected, creating a new one
            response = client.create_game_session(
                MaximumPlayerSessionCount=maximumPlayersBySession,   # only two players allowed per game
                FleetId=multiplayerFleetID
            )
            selected_game_session = response["GameSession"]
        
        else:
            # We grab the first session we find and join it
            selected_game_session = game_sessions[0]

        # There isn't a logical way selected_game_session could be null at this point
        # but it's worth checking for in case other logic is added
        if selected_game_session: 
            # Now we have a game session one way or the other, create a session for this player
            response = client.create_player_session(
                GameSessionId=selected_game_session["GameSessionId"],
                PlayerId=context.aws_request_id
            )
            response = response["PlayerSession"]
            # datetime is not JSON serializable, so we cast it manually 
            response["CreationTime"] = str(response["CreationTime"])
            return response
        
        else:
            return {
                "statusCode": 500,
                "body": "Unable to find game session, check GameLift API status"
            }
        
    except Exception as e:
        return {
            "statusCode": 500,
            "body": str(e)
        }