Which front-end optimization technique allows parallel downloads of resources from different domains to improve page rendering time?

Which front-end optimization technique allows parallel downloads of resources from different domains to improve page rendering time?

• A. HTML minification
• B. Domain sharding
• C. Image compression
• D. Cache busting

Answer: (B)

Domain sharding enables parallel downloads by serving resources from multiple domains, taking advantage of per-domain connection limits in browsers. Since browsers restrict how many simultaneous connections they open to a single domain, splitting assets across several domains lets the browser open more connections at once and fetch resources in parallel, which can speed up page rendering on HTTP/1.1. This technique was commonly used in the past to reduce latency for many small assets. However, with HTTP/2 and HTTP/3, multiplexed connections diminish the benefit of sharding, and the extra DNS lookups and TLS handshakes can offset gains. The other techniques—minifying HTML, compressing images, and cache busting—affect payload size or cache behavior, not the parallelism of downloads across domains.

Domain sharding enables parallel downloads by serving resources from multiple domains, taking advantage of per-domain connection limits in browsers. Since browsers restrict how many simultaneous connections they open to a single domain, splitting assets across several domains lets the browser open more connections at once and fetch resources in parallel, which can speed up page rendering on HTTP/1.1. This technique was commonly used in the past to reduce latency for many small assets. However, with HTTP/2 and HTTP/3, multiplexed connections diminish the benefit of sharding, and the extra DNS lookups and TLS handshakes can offset gains. The other techniques—minifying HTML, compressing images, and cache busting—affect payload size or cache behavior, not the parallelism of downloads across domains.