We use a process called replication in order to keep all of our game’s data synchronized with all of our players.

A simple example of replication is Roblox’s character system. Whenever a player moves around, their movements are sent from their client to the game’s server and then the server will send that data to all other players. This allows each player to see each other’s movements in real-time!

Examples of Replication

We can look at a few systems in Roblox which automatically handle replication for us to better understand this concept.

Leaderstats

Do you know that little leaderboard you see at the top right corner of many games? That’s referred to as the leaderstats.

The process of adding a Player to the leaderstats goes as follows:

1. Create a Folder named “leaderstats” and parent it to the Player
2. Create a NumberValue, give it a name, and parent it to the leaderstats Folder

Once you’ve done this, you can change the value of the NumberValue at any time, and that will be replicated to all players. See, you’re not handling the replication, you’re just modifying the value of an object and Roblox handles the rest.

Workspace

Whenever a player joins the game, all the contents of the Workspace are replicated to the player. If you make any changes to the Workspace from the server, such as deleting or adding an object, these changes will automatically be replicated to all current and future players.

Services

Many Services will instantly replicate their contents to the player upon joining and continue replicating to them as well.

• Workspace
• Players
• Lighting
• ReplicatedFirst
• ReplicatedStorage
• StarterGui
• StarterPack
• StarterPlayer
• SoundService
• Chat

How to Replicate Data

First, let’s quickly lay out the basics of networking on Roblox. If you want a more thorough explanation, you can check out this networking article!

Roblox has two remote objects which enable communication between the Client (Player) & Server (Game):

• RemoteEvent: Server -> Client | Client -> Server
• RemoteFunction: Server -> Client -> Server | Client -> Server -> Client

Now that we understand the basics, let’s create a scenario that would require replication.

Replication Usage Scenario

Let’s say we have a Wave Defense game and we want to display the current wave to every player. For further clarification, we want to also notify the player of the current wave, each time it increases.

Currently, only the Server knows what the current wave is because it’s stored and handled within a script there.

Let’s say the script below is a current example of our script which handles the waves.

local wave = 1

while true do
    wave += 1
    task.wait(5)
end

This example shows that every 5 seconds the wave will increase by 1.

If we want to replicate the wave to each player, we must use a Remote Event. Using the Remote Event we can notify all players of the current wave, each time it increases. And upon a player joining, we want to notify them of the current wave as well.

local Players = game:GetService("Players")

local WaveRemote = ReplicatedStorage.Remotes.WaveRemote

local wave = 1

while true do
    wave += 1
    WaveRemote:FireAllClients(wave)
    task.wait(5)
end

Players.PlayerAdded:Connect(function(player)
    WaveRemote:FireClient(player, wave)
end)

From the client, we must then listen to the Remote Event and we’ll be notified each time the wave has been changed.

Conclusion

Replication is a relatively simple concept to understand once have you a good understanding of networking. You’ve likely already done some form of replicating but didn’t realize it was even called something specific.

When I first began fully understanding replication was when I began using ProfileService. This naturally stores each player’s data inside a table, rather than the NumberValue or other Value Objects I was using. It opened my eyes to realizing what Roblox automatically does for me.