Domain sharding is a front-end optimization (FEO) technique that distributes website resources (such as images, scripts, and stylesheets) across multiple subdomains. Web browsers limit the number of concurrent connections to a single hostname (typically 6-8). By using multiple subdomains, domain sharding circumvents this limitation, allowing the browser to open more parallel connections and download more resources simultaneously. This directly addresses the scenario's requirement to overcome connection limitations and improve page-rendering time by increasing parallel downloads.

A. HTML comments removal: This technique reduces the size of the HTML file by stripping out comments, which can slightly speed up its download, but it does not affect the browser's concurrent connection limit.

B. Image lazy loading: This defers the loading of images that are not in the initial viewport. It improves perceived performance by reducing the initial payload, not by increasing the number of simultaneous connections.

C. CSS import to link: This converts @import rules to tags, which allows CSS files to be downloaded in parallel rather than sequentially. While it improves parallelism, it is specific to CSS and does not solve the overall browser connection limit for all resources like domain sharding does.

1. Citrix ADC 13.1 Product Documentation: In the section on Front End Optimization

the feature is explicitly defined.

Source: Citrix ADC 13.1 > Optimization > Front End Optimization > "Configure a front end optimization action"

Quote/Reference: "Domain sharding. A web browser limits the number of connections to a domain. You can use domain sharding to increase the number of connections. You can specify up to four domain names." This directly confirms that domain sharding is the feature used to overcome browser connection limits.

2. Citrix ADC 13.0 Product Documentation: The purpose of other FEO features is also clearly defined

showing why they are incorrect for this specific scenario.

Source: Citrix ADC 13.0 > Optimization > Front End Optimization > "Front end optimization"

Quote/Reference: The documentation describes "Remove HTML comments" as a technique to reduce file size and "Lazy load images" as a method to defer loading of images until they are needed

distinguishing their purpose from that of domain sharding.