[buro9]

* ESI support is really nice (if you're an API designer, you can really go nuts on this and make a super simple API do some very complex things or expressive composition from lots of simple calls)

* More fine-grained control of your caching is possible

* Easier to express normalisation of requests (increase your cache hit rate and protect your underlying origin from malicious requests by discarding cache busters)

* Inline C means you can do things like move your authentication to the edge

* In theory if you have enough RAM you can go faster than nginx's on-disk... in practice the sweet spot for the gain is small and they're both on par

But then... it comes with disadvantages too. Like most Varnish services would never let you do the nice Inline C stuff because no-one in their right mind would run untrusted code in their environment where it could impact another customer. If you see a provider do this (at any price point), avoid them.

[ruben_varnish]

Since 3.0 you have VMODs, to counter for the well-founded lack of Inline C support around. These Varnish modules will extend VCL with C, C++ or even Rust libraries on a safer manner: https://varnish-cache.org/vmods/

If you make your own VMOD(can take from a few hours to days), make sure to send a PR and add it to the directory above (IOW: share it) :)

[jimjag]

"In theory if you have enough RAM you can go faster than nginx's on-disk... in practice the sweet spot for the gain is small and they're both on par"

Not in theory, but in reality. Even if you don't, varnish's file on-disk implementation is just as good as nginx's if not better.

The idea behind a cache is to increase performance. If that is the priority then you would pick a design and implementation geared towards that problem set. Sure you can say "Well, nginx or httpd is 'good enough'" and that would be right. But when nginx or httpd aren't good enough, you need varnish. And even when you don't need varnish, it is often a better architectural design to break out specific functionality (best of breed).

[tomschlick]

Thanks for the detailed list! ESI looks pretty sweet so I'll have to take a look at that as we scale out our API in the coming months.