Apache Traffic Server is a fast, scalable and extensible caching proxy server that supports HTTP/1.1 and HTTP/2. The software stores frequently requested pages, images and web-service responses to reduce response times, server load and bandwidth, and adds proxy features such as keep-alive connections, content filtering and load balancing. Plug-in APIs make it possible, for example, to modify HTTP headers or add custom cache algorithms. Large CDNs and content providers use it as a building block. It is software that you install and operate yourself, not a hosted service.
Apache Traffic Server is a project of the Apache Software Foundation, a US-based foundation, and is released under the Apache License 2.0. Because you run it on your own infrastructure, you decide where traffic and cache reside, for example with a European hosting provider or in your own data centre. No vendor processes your data. For European organisations, it is therefore an open-source option where the foundation's jurisdiction says little about where the data sits, which your own deployment determines.