Web applications, a lot of that expense and effort may be related to scaling, which is the capability of a system to handle an increasing amount of work gracefully or to be readily enlarged
20. where are we it do?
1. staff can call backends as before
2. staff can call workflows via the
workflow queue
3. staff can manage workflows in
Redis
21. problem asynchronous callbacks
1. staff starts a workflow
2. staff calls some external API
3. the external API somehow notifies
us (file attachment, email, URL
callback, ...) about progress
4. staff needs to continue in the
workflow
22. how do staff correlate messages
1. the backend daemon for the
callback polls a view in
2. staff can search for any value in
the request they sent
3. staff can search for the very value
this external API uses as correlation
_id