Q1. What is idempotency and which HTTP methods are idempotent?
An operation is idempotent when performing it multiple times produces the same server state as performing it once. - GET, HEAD, PUT and DELETE are idempotent by HTTP sema...
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Q2. What happens when you type a URL into a browser?
The browser parses the URL, then finds the server's IP: it checks its cache, the OS cache, `/etc/hosts`, then asks a resolver, which recurses from the root servers throug...
Q3. What is the difference between HTTP 401 and 403?
401 Unauthorized means the request lacks valid authentication credentials. The client should authenticate and retry, and the response should include a `WWW-Authenticate` ...
Q4. What does a CDN cache and how does it help?
A content delivery network caches content on edge servers close to users. It serves static assets such as images, CSS, JavaScript and fonts, and can cache dynamic respons...
Q5. Explain the TLS handshake and what it protects.
TLS provides confidentiality, integrity and authentication for a connection. In TLS 1.3 the handshake is one round trip before application data. 1. The client sends a Cli...
Q6. When should you use PUT, PATCH or POST?
- POST creates a subordinate resource or triggers a non-idempotent action. The server assigns the identifier and returns 201 with a `Location` header. - PUT replaces the ...
Q7. Which HTTP status codes should a REST API return?
Group them by intent and be consistent: - 2xx success: 200 OK, 201 Created (with `Location`), 202 Accepted for async work, 204 No Content after DELETE. - 3xx: 301/308 for...
Q8. How do HTTP caching and CDNs improve performance?
Caching avoids re-downloading assets and is one of the cheapest performance wins. Use content-hashed filenames with a long Cache-Control: public, max-age=31536000, immuta...
Q9. How does HTTP caching work with Cache-Control and ETag?
HTTP caching lets browsers and proxies reuse responses. `Cache-Control` sets the policy: - `max-age=300`: fresh for 300 seconds; no revalidation needed. - `s-maxage`: ove...