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Varnish ESI block

Edge Side Includes (ESI) are special directives that you can use to include web pages in other web pages.

An example:

<div>
  <esi:include src="http://domain.com/index.php/page_cache/block/esi/blocks"/>
</div>

Varnish fetches content from http://domain.com/index.php/page_cache/block/esi/blocks and replace the <esi> tag with it.

Commerce and Varnish ESI

The Commerce framework creates an ESI tag when the following conditions are met:

Example

cms_index_index.xml:

  <referenceContainer name="content">
      <block class="Magento\Framework\View\Element\Template" template="Magento_Paypal::esi.phtml" ttl="30"/>
   </referenceContainer>

In the example above, the block element adds content from the esi.phtml template to a homepage and Varnish automatically updates it every 30 seconds.

Limitations

Currently, Varnish does not support ESI over HTTPS so it automatically switches to HTTP.

Magento\PageCache\Observer\ProcessLayoutRenderElement:

    private function _wrapEsi(
        \Magento\Framework\View\Element\AbstractBlock $block,
        \Magento\Framework\View\Layout $layout
    ) {
    ....
        // Varnish does not support ESI over HTTPS must change to HTTP
        $url = substr($url, 0, 5) === 'https' ? 'http' . substr($url, 5) : $url;
        return sprintf('<esi:include src="%s" />', $url);
    }