Varnish ESI Theme Context for Magento 2

Ensures correct theme context and cache segmentation for Varnish ESI block requests in multi-theme Magento setups.

Problem

When Varnish fetches ESI blocks via /page_cache/block/esi, the request does not carry any theme context. In a multi-theme store (e.g. Vendor/base and Venor/balckfriday), ESI blocks may be rendered and cached using the wrong theme, causing incorrect markup or broken styles.

Additionally, blocks with ttl are rendered inline during full-page generation even though they will be replaced by <esi:include> tags — wasting server resources.

Solution

This module solves both issues with three components:

1. Observer: ProcessLayoutRenderElement

Replaces the core Magento\PageCache\Observer\ProcessLayoutRenderElement (disabled in frontend scope). Adds an esi_theme parameter directly to the ESI URL during <esi:include> tag generation, so the theme path is carried through to the ESI request.

2. Plugin: RestoreEsiContextPlugin

Before plugin on Magento\PageCache\Controller\Block\Esi::execute(). Reads esi_theme from the request, sets the design theme via DesignInterface::setDesignTheme(), and adds a layout cache key (esi_theme_{path}) so layout cache is segmented per theme.

3. Plugin: SkipRenderLayoutElementPlugin

Around plugin on Magento\Framework\View\Layout::renderNonCachedElement(). When Varnish full-page cache is active and the page is cacheable, blocks with a TTL are skipped (return empty string) since they will be served via ESI includes instead.

Known Issues with Third-Party Modules

Amasty: Incorrect Entity-Specific Handle Registration

Warning: Avoid using Amasty modules if you want your site to be solid and have good performance.

Amasty modules (amasty/module-shop-by-brand, amasty/shopby) have a bug in their category controllers where they call addPageLayoutHandles() with both type and id parameters in a single call without setting $entitySpecific = false:

// Amasty (BROKEN) — marks ALL handles as entity-specific, including page-type handles
$page->addPageLayoutHandles(['type' => $type, 'id' => $category->getId()], 'catalog_category_view');

Magento core does this correctly with separate calls:

// Magento core (CORRECT) — type handles are NOT entity-specific, only id handles are
$page->addPageLayoutHandles(['type' => $pageType], null, false);
$page->addPageLayoutHandles(['id' => $category->getId()]);

This causes catalog_category_view_type_layered to be registered as an entity-specific handle. Magento's ProcessLayoutRenderElement observer then strips it from ESI URLs via array_diff(), so when Varnish fetches the ESI block, the layout is loaded without the layered navigation handle, resulting in broken block rendering on category and brand pages.

Installation

composer require hryvinskyi/magento2-esi-page-layout
bin/magento module:enable Hryvinskyi_EsiPageLayout
bin/magento setup:di:compile
bin/magento cache:flush

Configuration

No configuration required. The module activates automatically when Varnish full-page cache is enabled.

Requirements

• Magento 2.4.x
• PHP 8.1+