Daikombat Server

Daikombat Server is the server code repository for a simple Doom-like online shooter game with a non-stop death-match mode. It is built using Maven, Netty, Spring, and Java 14. Client/desktop code is also publicly available on GitHub.

Prerequisites

• Java 14
• Maven 3.6.3

Architecture overview

The server opens a TCP connection and serves in-game events as protobuf messages(find .proto schema in schema module). The client publishes game commands and then subscribes to server events by collecting them in an in-memory queue that is meant to be polled during game rendering. All communications (server-to-client and client-to-server) are totally non-blocking.

Known issues

• TCP is a bad choice for fast-paced online shooter games due to head-of-line blocking. In the future, the protocol is likely to be changed to either UDP or QUIC.
• The server is totally not scalable at this moment. High availability and load balancing are not provided.
• The server is NOT authoritative
• Basic anti-cheat

Configuration

Game server can be configured using the following environment variables:

• GAME_SERVER_PORT TCP server port at which client connections are going to be accepted. Default - 7777.
• GAME_SERVER_GAMES_TO_CREATE Games to create. Default - 10.
• GAME_SERVER_MAX_PLAYERS_PER_GAME Maximum number of players to join a game. Default - 25. Total number of players on the server is GAME_SERVER_GAMES_TO_CREATE*GAME_SERVER_MAX_PLAYERS_PER_GAME.
• GAME_SERVER_MOVES_UPDATE_FREQUENCY_MLS Frequency(in milliseconds) at which server notifies players about other players' positioning on the map. Default - 50.
• GAME_SERVER_MAX_IDLE_TIME_MLS Maximum idle time(in milliseconds) for a player. "Idle" - no network activity, which includes in-game events + ping responds. For example, if player connects to a game and doesn't move but responds to PING requests, then it's NOT considered idle. This check is mostly needed when a TCP connection was closed abruptly(no FIN). Default - 10_000.
• GAME_SERVER_DEFAULT_SHOTGUN_DAMAGE Gunshot damage. Default - 20.
• GAME_SERVER_DEFAULT_PUNCH_DAMAGE Punch damage. Default - 50.
• GAME_SERVER_PIN_CODE Server access pin code(digits only, no less than 4). Used in HMAC that is appended to every message. Default - 5555.
• GAME_SERVER_FAST_TCP Enables fast TCP configurations(used mostly for testing, not recommended to be set to false in prod). Default - true.
• GAME_SERVER_FRAGS_PER_GAME Frags to win a game. Default - 25.
• GAME_SERVER_COMPRESS Turns on protobuf data compression using zlib(used mostly for testing, not recommended to be set to false in prod). Default - true. Warning. This value has to match CLIENT_COMPRESS. If client compresses data but server does not then communication will fail.
• GAME_SERVER_QUAD_DAMAGE_SPAWN_MLS Time (in millisecond) it takes to spawn a quad damage power-up orb. Default - 30_000.
• GAME_SERVER_QUAD_DAMAGE_LASTS_FOR_MLS Time (in millisecond) quad damage lasts for. Default - 10_000.
• GAME_SERVER_POWER_UPS_ENABLED Turns power-ups on and off. Default - true.
• SENTRY_DSN Sentry DSN. Not specified by default.

Game client is also configurable through environments variables:

• CLIENT_MAX_SERVER_INACTIVE_MLS Maximum server inactivity time(in milliseconds). Default - 10_000.
• CLIENT_COMPRESS Turns on protobuf data compression using zlib(used mostly for testing, not recommended to be set to false in prod). Default - true.
• CLIENT_FAST_TCP Enables fast TCP configurations(used mostly for testing, not recommended to be set to false in prod). Default - true.

Deployment and integration

Game client integration

All submodules, including network client, can be used as maven/gradle dependencies using jitpack.

Docker

Server image is deployed on every release to Github container registry. A sample docker-compose file can be found in the root folder.

Monitoring

Server monitoring

JVM metrics

Server JVM metrics can be monitored through JMX remotely. See docker-compose file. In the sample, JMX agent is running on port 9999 listening to incoming connections initiated by 127.0.0.1. If server is running in the cloud, then it's possible to port-forward JMX using the following command:

ssh -L 9999:127.0.0.1:9999 <user>@<remote_host>

Heap dumps

Apart from JMX metrics, the server is configured to drop a heap dump file on out-of-memory.

Micrometer

All command handlers publish Micrometer timer metrics through JMX. See "metrics" in Jconsole "MBeans" tab.

Sentry

All errors are automatically published to Sentry. See SENTRY_DSN env var.

Client monitoring

GameConnection.java has networkStats field that gathers basic network stats including:

• ping(current value + 50th, 75th, and 99th percentiles)
• number of sent protobuf messages
• number of received protobuf message
• total protobuf outbound payload size(uncompressed)
• total protobuf inbound payload size(uncompressed)

Development

Handy Maven commands

Here are some commands that might be useful while coding.

Update all submodules' versions

mvn versions:set -DnewVersion=<version>

Run static code analysis

mvn spotbugs:check 

Update protobuf schema

rm .\schema\src\main\java\com\beverly\hills\money\gang\proto\* 
protoc --java_out=./schema/src/main/java/ .\schema\src\main\resources\server-response.proto
protoc --java_out=./schema/src/main/java/ .\schema\src\main\resources\server-command.proto

Testing and QA

The project provides good quality of service by:

• Unit and integration testing (Junit). Minimum coverage requirements can be found in Jacoco configs.
• Static code analysis (Spotbugs)
• Dependency check (Snyk)
• Resiliency testing (ToxiProxy)
• Load testing. See com.beverly.hills.money.gang.bots.BotRunner for spawning dummy bots
• Game client manual acceptance testing is also involved in the process. Dev mode is provided for the desktop version.