Lemmy Project Structure

A link aggregator and forum for the decentralized web. A high-performance Rust application built with Actix-web and Diesel, focusing on ActivityPub federation.

Updated 2025-12-30

#lemmy #rust #actix-web #diesel #activitypub #federation #reddit-alternative

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Project Directory

lemmy/

crates/

Cargo Workspace

server/

Main Application Entry

api/

REST API Handlers (Actix)

apub/

ActivityPub Protocol

db_schema/

Diesel Schema & Types

db_views/

Postgres View definitions

migrations/

SQL Migrations (Diesel)

docker/

Deployment & Federation tests

Cargo.toml

diesel.toml

Repository Info

Repository-LemmyNet/lemmy
Stars-10k+
License-AGPL-3.0
Last Analyzed-December 2025

Tech Stack

Language-Rust
Web Framework-Actix-web
ORM-Diesel
Database-PostgreSQL
Protocol-ActivityPub
Format-JSON-LD

Architecture Notes

Lemmy is built as a modular **Cargo Workspace**. It relies heavily on **Diesel** for a type-safe interface to PostgreSQL. A distinct feature of Lemmy's architecture is its heavy use of **PostgreSQL Views** (db_views) to handle complex aggregations (like calculating hot-ranking scores or unread counts) efficiently at the database level. Federation is handled by the apub crate, which implements the ActivityPub standard.

Key Directories

crates/apub/-The federation engine. Handles sending and receiving activities (Like, Post, Follow) between Lemmy instances.
crates/db_views/-Contains definitions for materialized and non-materialized views that simplify complex queries for the API.
crates/api/-The Actix-web server implementation. It defines the JSON-RPC-like REST API that the frontend (lemmy-ui) consumes.

Why This Structure?

Lemmy is a prime example of a 'Social Systems' architecture in Rust. It shows how to combine high-performance web frameworks with a robust, type-safe database layer to build a decentralized platform.

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