DEV Community: Joshua

Why static diagrams fail: simulating an e-commerce checkout flow in Robust Design

Joshua — Tue, 23 Dec 2025 14:44:58 +0000

It’s time we move on from static diagrams as the primary reference for demonstrating system design concepts. Sure, it makes sense to use it as a rapid proof of concept, but it fails when you genuinely want to understand how the system behaves. We have online resources to help you run and simulate code and provide concrete proof that it works, and it’s time we have one for system design. You could draw a diagram with a line to the load balancer, another to the server, and another to the database, but it doesn’t fully show what’s happening. We should be able to simulate, verify, and debug the system with minimal effort before we build it. It doesn’t make sense to create a system solely from a diagram.

As coding becomes more accessible, the shift will move toward system design. Entry-level roles will now be required more often to understand system design concepts and build systems. Being able to code alone is not enough; we also need tools that help those who are just starting to understand the ins and outs of a system entirely.

Robust Design solves this problem for both experienced and entry-level engineers. With Robust Design, you’ll be able to fully design the flow of how a system should behave and the flow of requests. After creating your system, you can simulate it to obtain real-time results rather than drawing a diagram. Worried about load during traffic hours? Add a load balancer and simulate it. Want to see how async request works with a server? Add a message queue and see how it affects the response time.
Here’s an example of Robust Design applied to a simple e-commerce system design flow.

To first design this system, we need to define the process.
First, we have three requests:

We need to allow users to check their inventory -> /inventory/check
We need to allow users to order and check out an item -> /orders/checkout
We need to allow users to pay for items -> /payments/process

Next, we need to route each request to the appropriate service. We route these requests through a load balancer using path-based routing. Finally, each request is saved to the database, or we retrieve data from it if the request is GET.

Now comes the fun part, simulating it. We can simulate each request individually by connecting it to the load balancer and clicking Run Simulation; we’ll then see the request flow. We’ll do that for all three and confirm that the design actually works and is valid. After this, we’ll then proceed to build the system. Diagrams alone cannot give you this confirmation. It’s time we innovate and develop better methods for designing systems.

robustdesign.io

Creating a simplified LinkedIn-style social architecture

Joshua — Tue, 16 Dec 2025 14:17:37 +0000

Two weeks ago, I launched my platform, which helps anyone learning system design or preparing for system design interviews simulate and validate their systems.

I created this platform because I've always been awful at system design interviews. I remember interviewing at LinkedIn and failing the system design interview, which was to design a URL shortener, probably the most straightforward system design interview question anyone can get.

Using my platform, it's helped me better understand system design than ever, and I've used it to create a simplified LinkedIn-style social architecture.

It has the same functionality as:
Creating a profile
Adding a connection
Sending a message
Commenting on a post
Liking a post

It also uses message queues, which I simplified in my platform, to handle background tasks such as notifications and analytics.

I created this platform using ReactJS for the frontend, Flask for the backend, and Judge0 for the code execution. My goal is to move from Flask to Go eventually. I'd like to hear your feedback on this.

Do you think there needs to be a change in how system design interviews are conducted?

Also, here is a demo of the platform simulating a simple Netflix architecture: https://www.youtube.com/watch?v=n1KDZoS--yw

Design and Simulate System Architecture before building

Joshua — Mon, 01 Dec 2025 13:28:02 +0000

I've built a platform that lets you design, simulate, and validate your system architecture before you write a single line of production code.

What I built

Robust Design An interactive canvas for designing and simulating system design architecture

The Story

After leaving Microsoft in May for a mental break, the thought of future interviews brought back a familiar dread: system design. I've always struggled with these interviews, and I've never found a resource that went beyond lectures or courses. I actually needed an interactive platform to design and test the systems I created.

So, I built Robust Design.

Right now, it's the ultimate tool for interview preparation. However, my long-term vision is to transform it into the Figma for System Architecture—a collaborative platform essential for every engineering team.

Current features

Drag-and-Drop Canvas: Easily assemble components (User Requests, APIs, Load Balancers, Databases).
Visual Connectivity: Define component relationships with clear, visual connections.
Real Code Simulation: Inject real Python code to model business logic and API behavior.
Run Simulations: Instantly test your designs under various conditions.
Instant Feedback: Get immediate validation on whether your architecture performs as expected.

Tech Stack

Frontend: Nextjs + React + Typescripts
Backend: Flask + Firebase
Hosting: Vercel + Railway

Try It Now & Give Feedback

I have a two-minute tutorial you can try for free, no sign-up required.

If you want to unlock all features, including the ability to simulate an API design with your own Python code fully, you can sign up for free.

I am actively building and expanding this project, and your feedback is invaluable. Don't hold back! Whether you hate the UI colors, think a feature is missing, or have ideas for team collaboration, please let me know.

Link: Robust Design
Docs: https://docs.robustdesign.io

LinkedIn: https://www.linkedin.com/in/youngjoshuaa/