How to Add Online Multiplayer to a Small Indie Game

Overview

Building online multiplayer for a small indie game is less about chasing a feature-rich fantasy and more about choosing a reliable, maintainable path. This guide walks you through a practical, engine-agnostic approach: selecting a networking model, designing a lean authoritative server, handling latency with prediction and interpolation, and getting your game from prototype to a launch-ready multiplayer experience.

Decide on a Networking Model

Your model shapes every other decision:

• Authoritative server (recommended for most small games)

  • A centralized server validates game state, processes inputs, and broadcasts updates.
  • Pros: cheat resistance, consistent rules, easier to balance.
  • Cons: requires server hosting and careful security.

• Listen server / host migration (simpler, but riskier)

  • One player’s machine runs the game server logic.
  • Pros: simple setup, low cost.
  • Cons: higher hosting load on the host, NAT issues, cheating risk.

• Peer-to-peer with relay (for very small, non-critical multiplayer)

  • Clients exchange state and rely on a relay for connectivity.
  • Pros: minimal backend.
  • Cons: synchronization complexity, higher cheating risk, NAT traversal burdens.

• Relayed matchmaking services (fastest path to playable)

  • Use a service to handle lobby, NAT traversal, and relay.
  • Pros: QoS, reduced maintenance.
  • Cons: ongoing service cost, potential vendor lock-in.

Recommendation: start with an authoritative server model (even a small, cost-efficient server) and add a relay or matchmaking service if you need scale or faster setup.

Core Architecture

Clarify data flow and responsibilities:

• Client

  • Collects local input and renders predicted state.
  • Sends input commands to the server at a steady tick rate.
  • Receives authoritative state updates and reconciles client state.

• Server

  • Runs the game loop at a fixed tick rate (e.g., 20–60 Hz).
  • Validates inputs, updates world state, and broadcasts state snapshots.
  • Enforces game rules and detects/mitigates cheating.

• Communications

  • Transport: UDP-based for low latency or a hybrid UDP/TCP approach (depending on engine and needs).
  • Protocol: define a small, stable set of message types (Join, Input, StateUpdate, Ping/Pong, Leave).

• Data model

  • Messages should be compact: player inputs, entity positions, actions, and timestamps.
  • Use sequence numbers and versioning to enable reconciliation and latency handling.

Implementing a Minimal, Authoritative Server

A lean blueprint you can adapt to most engines or custom stacks:

• Establish a fixed tick loop on the server.

• Every tick:

  • Apply received inputs from clients.
  • Update game state deterministically.
  • Broadcast the new authoritative state to all clients.

• Client responsibilities:

  • Send inputs each tick.
  • Render locally with prediction and later reconciliation when server state arrives.

• State updates

  • Include only necessary entities and fields (position, velocity, action states).
  • Use delta compression if possible to minimize bandwidth.

• Security basics

  • Validate every input (e.g., bounds checks, collision rules).
  • Enforce server-authoritative decisions to prevent speed hacks or teleportation.

Client-Side Prediction, Interpolation, and Reconciliation

Latency can break immersion if not handled cleanly:

• Client-side prediction
  • Apply local input immediately to keep feel responsive.
• Server reconciliation
  • When a server state arrives, compare against predicted state.
  • If mismatches occur, rewind to server state and replay queued inputs.
• Interpolation
  • Smoothly interpolate between received states to avoid jitter.
  • Maintain a small buffered delay to absorb network jitter.

Tips:

• Keep a tight tick rate and use fixed physics steps on both client and server.
• Separate input timeline from rendered frames to minimize perceived lag.

Security and Cheating Prevention

Indistinguishable from online play, but you can reduce risk:

• Enforce server authority
  • Never trust client-side physics or game rules.
• Validate all inputs on the server
  • Apply sane limits (e.g., max speed, jump cooldown) and ignore impossible commands.
• Use checksums or state validation
  • Periodically verify critical state (e.g., player health, inventory).
• Anti-tamper and obfuscation
  • Consider lightweight obfuscation or integrity checks where feasible.
• Logging and anomaly detection
  • Track suspicious patterns (impossible movement, rapid input bursts) for review.

Tools and Services to Accelerate Development

Leverage existing tools to reduce setup time:

• Networking libraries and backends
  • Low-level: ENet, RakNet, or WebSocket for Web-based games.
  • Backend services: Nakama, Colyseus, PlayFab, Photon, or a custom Node.js/Go server.
• Engine-agnostic patterns
  • Use a simple message protocol, a fixed server tick, and a clear input/state separation to stay engine-agnostic.
• Hosting options
  • Dedicated VPS or cloud instances (AWS, DigitalOcean, Linode) for the server.
  • Managed services for matchmaking or relays if you prefer not to run servers yourself.

Testing, Debugging, and Scaling

Validate multiplayer behavior early and often:

• Local hops
  • Run server and client on the same machine, then on a separate LAN machine to simulate real latency.
• Latency simulation
  • Introduce artificial latency and packet loss to observe reconciliation, prediction效果, and correction behavior.
• Automated tests
  • Create tests for input handling, state updates, and edge cases (lobby joins, disconnects, host migration).
• Profiling
  • Monitor bandwidth per client, tick time, and CPU cost of the server loop.
• Scaling plan
  • Start with a single regional server; plan for a hot-swappable region or a simple load-balanced setup as player count grows.

Deployment Roadmap

• Phase 1: Prototype
  • Build a minimal server and a basic client that can join a lobby, send inputs, and display server-corrected state.
• Phase 2: Refinement
  • Implement prediction, reconciliation, and interpolation. Harden input validation.
• Phase 3: Security and QA
  • Add basic anti-cheat measures and automated tests. Conduct internal playtests focusing on fairness and stability.
• Phase 4: Deployment
  • Launch with a single region, monitor metrics, and gradually scale or add relays/matchmaking as needed.

Common Pitfalls and How to Avoid Them

• Overcomplicating early
  • Start small: a single, authoritative server with a simple set of inputs and a fixed tick rate.
• Underestimating latency effects
  • Implement prediction and reconciliation from day one to avoid a jarring feel.
• Neglecting security
  • Favor server-side checks over client-side trust; validate everywhere.
• Burnout from maintenance
  • Use existing services where possible; design a clean protocol and modular server code to ease future changes.

Next Steps and Resources

• Pick a target engine or framework and map these concepts to its networking APIs.
• Try a small prototype with a basic arena or co-op mode to validate the flow before expanding features.
• Explore open-source backends like Nakama or Colyseus to compare workflows and integration points.
• Read up on authoritative server patterns and latency mitigation strategies to deepen the implementation.