What is Varnish?
Varnish is an HTTP reverse proxy that sits in front of your web server and serves a full-page cache. When a page can be cached, Varnish stores the rendered HTML in memory and serves subsequent requests directly - without ever touching PHP or the database. This reduces response times and server load on read-heavy sites.
For storefronts such as Magento, Shopware and WooCommerce, this keeps the site fast under heavy traffic, which matters most during campaigns and sales peaks.
Because Varnish caches whole pages, it is most effective for storefronts where many visitors see the same anonymous pages (product and category listings, the home page). It uses a configuration language called VCL to decide what to cache, what to bypass, and when to purge.
On TurboStack
Varnish is provided as a per-application technology with broker-level tuning at the host.
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You enable Varnish for an application in the application configuration. TurboStack then provisions and manages it for that site.
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Varnish listens on port 6081 by default. Requests reach Varnish first, and it serves them from cache or forwards them to the web server behind it.
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TurboStack ships an app-aware VCL tuned for PHP storefronts: it bypasses the admin and cart, keeps logged-in and checkout traffic dynamic, and supports cache purging from the application.
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It is intended for PHP storefronts - primarily Magento and Shopware, and optionally WordPress.
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Host-level tuning lives under Advanced > Varnish Options, where you can set the cache size (auto-sized), provide custom VCL, and choose the Varnish type (OpenSource or Enterprise).
Warning
Do not put Varnish in front of Node.js applications or Odoo. Its full-page caching is built for PHP storefronts and will break apps that expect every request to reach the backend.
Best practices
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Use Varnish for high-traffic, read-heavy PHP storefronts where anonymous visitors see the same pages.
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Rely on the TurboStack app-aware VCL rather than hand-writing rules - it already bypasses admin and cart and supports purging.
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Make sure your application issues cache purges on content changes so visitors do not see stale pages.
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Leave the cache size auto-sized unless you have a clear reason to override it.
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Only reach for custom VCL when you have an expert use case; mistakes there can cache the wrong content.