README.md

Rusty Mailer

A simple but fault-tolerant and well-tested email delivery service.

About The Project

Rusty Mailer is a practice project using Rust, it's a simple email newsletter delivery service where users can publish newsletter issues to their subscribers. It features some degree of fault-tolerance and well-tested codebase. Built using Rust and Actix Web, it was a project from the book Zero to Production in Rust.

To achieve fault-tolerance, email newsletter deliveries are done asynchronously by queueing the delivery in the database, then background workers will dequeue it periodically.

The following is the diagram:

sequenceDiagram
    participant User
    participant Rusty Mailer
    participant Database
    participant Background Worker 1
    participant Background Worker 2
    participant Postmark
    
    User->>+Rusty Mailer: Publish new newsletter issue
    Rusty Mailer-)Database: Queue the newsletter deliveries
    Rusty Mailer->>-User: "Success, newsletters will go out shortly"
    loop Email Newsletter Delivery
      par
        Background Worker 1->>Database: Dequeue
        Background Worker 1->>Postmark: Send email newsletter
      and
        Background Worker 2->>Database: Dequeue
        Background Worker 2->>Postmark: Send email newsletter
      end
    end

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PostgreSQL table is utilized as the queue, background workers will pick 1 row to process everytime it does dequeue operation and then delete the row immediately after it succeeded processing. PostgreSQL's row-level locking is utilized to prevent multiple background workers from processing the same row, thus preventing duplicate email delivery.

The following diagram illustrates what would happen when there are 2 rows (row A and row B) in the table and two workers do dequeue operation concurrently:

sequenceDiagram
    participant Worker 1
    participant Worker 2
    participant Database
    
    par Worker 1 tries to process row A
      rect rgb(180, 150, 50)
        alt Row A is not locked
          Worker 1->>Database: Processes row A
        else Row A is locked
          Worker 1->>Database: Processes row B
        end
      end
    and Worker 2 tries to process row A
      rect rgb(50, 50, 50)
        alt Row A is not locked
          Worker 2->>Database: Processes row A
        else Row A is locked
          Worker 2->>Database: Processes row B
        end
      end
    end

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Built With

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Getting Started

Prerequisites

• Docker;
• Rust;
• SQLX-cli, install using cargo install sqlx-cli;
• PostgreSQL.

Running Locally

1. Clone the repo and cd into the directory;
2. Run the following command:

scripts/init_db.sh && scripts/init_redis.sh

3. Run cargo run
4. The web can be accessed at localhost:8081;
5. Go to localhost:8081/login to login, use "admin" for username, and "everythinghastostartsomewhere" for the password.

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Roadmap

• Deploy to a cloud provider
• Create automated deployment pipeline
• API docs (Swagger)
• Revamp UI

See the open issues for a full list of proposed features (and known issues).

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License

Distributed under the MIT License. See LICENSE for more information.

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Contact

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Acknowledgments

Much thanks to these people/organizations/resources that made this project possible to be as it is now!

• Zero 2 Production in Rust Book
• Luca Palmieri (Author of zero2prod.com)
• Rust Programming Language
• PostgreSQL
• Redis
• Actix Web
• Postmark
• OWASP Cheat Sheet Series
• Img Shields

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