It depends on the case, but an easy way to emit progress indicators in our system is to make the long-running service a generator. It looks like this:

    g = wym('/email') #=> Generator(id=<...>)
    g.on('value', (v) ->
        ...
    )

and /email looks like:

    function next(inp) { ... }
    return generator(next);

Sending values in uses a slightly different syntax, and manually walks the generator through. :)

A more trivial way is to pass in a callback for the service (we call them routes) to send its updates back to, but this requires more code to send values in.

Edit: to be clear, using a Generator as above isn't very microservice-ey and will trigger our framework to start tracking local state to keep the generator around, which it will auto-free when it believes it can. This is a necessary evil with any long-running code, though. Better is to break up the code so that it may be called multiple times to progress state and returning generator('/someRoute') if possible. :P