Cool, that all sounds perfectly doable with OCaml. The opam package index is your friend, search for mq, kafka, and so on.
With Scala if you want specialized streaming support, there are several good libraries to choose from, especially fs2. In OCaml we have the similar streaming library: [ANN] First release of streaming
If you want an HTTP server check Dream — Tidy, feature-complete web framework , it’s still unpublished, but very promising. For HTTP client use opam - piaf –it’s modern, pure OCaml, and should integrate well with Dream.