I’m shocked at how often this one question is asked in technical interviews everywhere (Amazon, Microsoft, Google & FAANG+ companies). What happens when you type a URL into your browser? Here’s how I would answer it: 1. Browser parses the URL - The browser identifies the components: scheme (https), domain (example. com), and path (/hello-world). 2. DNS lookup - The browser checks its cache or queries a DNS resolver (ISP or public DNS like Google’s 8.8.8.8) to translate the domain name into an IP address. - If not cached, the resolver performs a recursive DNS lookup, contacting root, TLD, and authoritative name servers. 3. Establishing a connection - A TCP connection is initiated between the browser and the server at the resolved IP address. - If the URL uses HTTPS, a TLS handshake is performed to encrypt the connection. 4. Sending the HTTP request - The browser sends an HTTP request with details like method (GET/POST), headers (e.g., User-Agent), and optional body data. - Example: GET /hello-world HTTP/1.1. 5. Server processes the request - The server identifies the resource from the request path and processes it. - For dynamic content, the server might query a database, run application logic, and generate the response on the fly. 6. Returning the response - The server responds with: - Status Line: Indicates success or failure (e.g., 200 OK, 404 Not Found). - Headers: Metadata like Content-Type (e.g., text/html) and caching instructions. - Body: The requested content (e.g., HTML, JSON, or image data). 7. Browser renders the content - The browser parses the HTML and makes additional requests for linked resources (e.g., CSS, JS, images). - Resources are rendered progressively, and JavaScript is executed to enhance interactivity. 8. Caching and Optimization - Browsers cache resources based on headers like Cache-Control. - CDNs (Content Delivery Networks) and edge servers may serve static content to reduce latency. Key Points for additional benefit: - Mention DNS caching at various layers (browser, OS, ISP). - Highlight the TLS handshake and its role in securing HTTPS connections. - Discuss CDNs and how they improve performance. - Touch on asynchronous resource loading (e.g., defer or async for scripts). - Bring up response codes and their significance (e.g., '200', '301', '503'). References for answer in the comments below.
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That is a really simple question that can get really messy, really quickly! I got this question once, but the interviewer asked to get into each aspect I was taking about, so ..network, bandwidth, tcp headers, so... DNS lookup! That is just the title, explain how it works, types of records, etc. Then explain both, tcp and TLS handshakes, what info is there, how CAs work.... All the way to getting your cat meme - encoding and compression included, the decomposition can get a bit brutal.
Nice article! Extending the design for further scalability, after the ip is resolved, you could be redirected to the cloudfront instead of pointing directly to origin servers. The cloud front may redirect you to the reverse proxy servers that may perform some validations like filter out ip addresses etc, and then finally based on specific route, the request is routed to your website servers. And there could be load balancers sitting on top of your cdn / reverse proxy servers.
I love this question as there is something every software engineer can demonstrate their expertise on whatever their role has been and you could fill a whole interview without getting much further than discussing the typing and letters appearing on the screen.
And before you even press the Enter key, there's a lot going on to facilitate Search, Auto-complete and checks against your browser history. It's a great question to hear how an engineer thinks through an end-to-end system. Thanks for sharing!
Your breakdown of the URL loading process is spot on and incredibly informative for anyone preparing for technical interviews! I have written a detailed article on the same topic - https://oxyprogrammer.com/demystifying-dns-understanding-domain-name-resolution
Great! Just to avoid a blind spot: in frontend-heavy roles, they might want to hear about rendering, in infrastructure, you might talk about OSI layers.
To ur step 3, a lot goes in. Complete PKI comes into play, and OSI of course.
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1wReferences for answer: https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/welcome-dns-service.html https://aws.amazon.com/blogs/mobile/what-happens-when-you-type-a-url-into-your-browser/