Ask HN: How to backup mysql and hadoop and mongodb in a consistent way?

A client asked me to take over that task. I'm searching for new inspirations / ideas of achieving this task without having a downtime. They're data is a mess, they have relations over all 3 database systems and need a consistent backup. Currently there's no backup at all :) Ofc i can shut them all down and then run a backup...

Any ideas for new approaches?

btw: It's hosted on aws instances (not aws managed stuff)