Delay node, with rate limit: how to check if every single message reached "the end" of the flow

[Colin]

Do you mean that, ideally, you want to not release the next message until the previous one has completed? If so then the current beta version of node red (v3.0 beta 4) has a fix to the delay node that allows you to feedback when the flow has completed to release the next one from the delay node. See Wait for payload to finish flow before passing another payload - #33 by Colin for a flow that works in the beta version (it didn't at the time of the post). Set the delay node to rate limit with a large timeout so it only releases messages if a message gets lost. Otherwise the next one will be released as soon as the previous one says it is complete. Note that the message sent back must be an empty message except for msg.flush.