Edge Side Includes

<h2 id="syntax">Syntax</h2>
<p>ESI element tags are inserted into HTML or other text based content during creation. Instead of being displayed to viewers, these ESI tags are directives that instruct an ESI processor to take some action. The <a href="/facts/XML/clNgUfWk">XML</a> based ESI tags indicate to the edge-side processing agent the action that needs to be taken to complete the page's assembly. One simple example of an ESI element is the include tag which is used to include content external to the page. An ESI include tag placed in-line within an HTML document would look like:<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a>
</p>
<esi:include src="http://example.com/1.html" alt="http://bak.example.com/2.html" onerror="continue"/>

<p>In this case the ESI processor would retrieve the src URL, or failing that the alt URL, or if that failed do nothing. The ESI system is usually a caching proxy server so it may have a local copy of these files which it can insert without going back to the server. Alternatively the whole page with the ESI tags may be cached, and only the ESI requests may be made to the origin server. This allows different caching times for different parts of the page, or different degrees of personalisation.
</p>
<h2 id="features">Features</h2>
<p>There are four main features in ESI:<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> 
</p>
<ul><li><i>inclusion</i> of page fragments, as illustrated above;</li>
<li><i>variables</i> which can be set from <a href="/facts/HTTP_cookie/o1laXyng">cookies</a> or <a href="/facts/HTTP_header/hEkcQe2f">HTTP headers</a> and then used in other ESI statements or written into markup;</li>
<li><i>conditions</i> so that different markup can be used based on variables, for example if a cookie is set or not;</li>
<li><i>error handling</i>, so that a <a href="/facts/Failover/Lw0rXfv9">failover</a> can be used if an origin server is unavailable.</li></ul>
<h2 id="alternatives">Alternatives</h2>
<p>The main alternatives to ESI are 
</p>
<ul><li>to do assembly on the <a href="/facts/Web_server/A4GS6thA">origin server</a> using <a href="/facts/Server_Side_Includes/389lK6mQ">Server Side Includes</a> and many types of <a href="/facts/Server-side_scripting/JnLx8FnL">server-side scripting</a>.</li>
<li>to use <a href="/facts/Client-side_scripting/psjqGKBx">client-side scripting</a> and techniques collectively known as <a href="/facts/Ajax_(programming)/cS0P0whT">Ajax</a> (see: <a href="/facts/Dynamic_web_page/psjqGKBx">Dynamic web page</a>) in the <a href="/facts/Web_browser/2pfyymLs">browser</a></li>
<li>to establish a protocol between origin and edge such that recurring content will be included on the edge automatically, as with Cloudflare's Railgun protocol <a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a></li>
<li>to do assembly in the browser using <a href="/facts/Web_components/zQzBNnef">web components</a>.</li></ul>

<h2 id="external-links">External links</h2>
<ul><li><a href="http://www.akamai.com/html/support/esi.html">Akamai's ESI developer resources</a></li>
<li><a href="http://www.w3.org/TR/esi-lang">W3C Note "ESI Language Specification 1.0"</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Mark Tsimelzon; Bill Weihl; Joseph Chung; Dan Frantz; John Brasso; Chris Newton; Mark Hale; Larry Jacobs; Conleth O'Connell (2001-08-04). "ESI Language Specification 1.0". W3C. Retrieved 2008-11-10. <a href="http://www.w3.org/TR/esi-lang" target="_blank">http://www.w3.org/TR/esi-lang</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Mark Tsimelzon; Bill Weihl; Joseph Chung; Dan Frantz; John Brasso; Chris Newton; Mark Hale; Larry Jacobs; Conleth O'Connell (2001-08-04). "ESI Language Specification 1.0". W3C. Retrieved 2008-11-10. <a href="http://www.w3.org/TR/esi-lang" target="_blank">http://www.w3.org/TR/esi-lang</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>"Mongrel ESI". <a href="https://code.google.com/p/mongrel-esi/" target="_blank">https://code.google.com/p/mongrel-esi/</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>"Varnish ESI features". Retrieved 2011-04-07. <a href="http://www.varnish-cache.org/trac/wiki/ESIfeatures" target="_blank">http://www.varnish-cache.org/trac/wiki/ESIfeatures</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>"EdgeSuite 5.0 ESI Extensions to the ESI 1.0 Specification" (PDF). Retrieved 2011-04-07. <a href="http://www.akamai.com/dl/technical_publications/akamai_esi_extensions.pdf" target="_blank">http://www.akamai.com/dl/technical_publications/akamai_esi_extensions.pdf</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>Mark Tsimelzon; Bill Weihl; Joseph Chung; Dan Frantz; John Brasso; Chris Newton; Mark Hale; Larry Jacobs; Conleth O'Connell (2001-08-04). "ESI Language Specification 1.0". W3C. Retrieved 2008-11-10. <a href="http://www.w3.org/TR/esi-lang" target="_blank">http://www.w3.org/TR/esi-lang</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>Mark Tsimelzon; Bill Weihl; Joseph Chung; Dan Frantz; John Brasso; Chris Newton; Mark Hale; Larry Jacobs; Conleth O'Connell (2001-08-04). "ESI Language Specification 1.0". W3C. Retrieved 2008-11-10. <a href="http://www.w3.org/TR/esi-lang" target="_blank">http://www.w3.org/TR/esi-lang</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
<li id="fn:8"><p>"Railgun™". June 2023. <a href="https://www.cloudflare.com/railgun/" target="_blank">https://www.cloudflare.com/railgun/</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li>
</ol>

Edge Side Includes open-in-new

Edge Side Includes