Just as a heads up when you're writing your own VCL, we don't allow
vcl_pipe in customer uploaded VCL.
The reason why:
vcl_pipe opens a raw TCP socket in the network, and that's not ideal when building a high scale CDN
The good news is that we've gotten really good at helping customers achieve their intended goals without using
vcl_pipe -- let us know what you're using pipe for now, and we can help implement the logic in some other way.