Question: We are choosing a CMS platform for a big old solution. It's preferable to have site **on-premise**, not in cloud (company policy) and a lifelong license.

Does anyone have experience with building a solution with similar characteristics on **Umbraco / Episerver / Sitecore / Sitefinity:**

~ 4-20 mln visits a day (3 sites)

~ 4000 requests/sec

~ 6 mln pages of content (search is needed in admin for all pages)

It seems to me that headless solution would be the most suitable (with layers of caching in-between).

But is it possible to implement everything on-premise:

* scalable solution (horizontally)
* efficient search
* recommendation system

Answer: 
All CMS vendors mentioned support both on-premise and cloud hosting and can easily handle such loads (if properly implemented).

Episerver has sophisticated search and recommendation engines, although those rely on cloud services even if the CMS itself is hosted on-premise.

A headless approach can be great from a technical/performance standpoint, but it does come with a risk of less user-friendly content authoring depending on the implementation.
The idea is to use combine `Rich Content Management facilities provided by CMS` +
`Unlimited scaling options and performance`([Content Delivery Networks](https://en.wikipedia.org/wiki/Content_delivery_network))

Content from [Sitecore](https://www.sitecore.com/) is published to CDN via [Uniform](https://uniform.dev/).
The result - best theoretically possible performance in any region in the world.

The specific architecture/design is to be used, though ([JAM Stack](https://jamstack.org/)).