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From Simon Calvin <scal...@hoganassessments.com>
Subject First time building a streaming app and I need help understanding how to build out my use case
Date Fri, 07 Jun 2019 19:39:24 GMT
Hello, everyone. I feel like I have a use case that it is well suited to the Kafka streaming
paradigm, but I'm having a difficult time understanding how certain aspects will work as I'm
prototyping.

So here's my use case: Service 1 assigns a job to a user which is published as an event to
Kafka. Service 2 is a domain service that owns the definition for all jobs. In this case,
the definition boils down to a bunch of form fields that need to be filled in. As changes
are made to the definitions, the updated versions are published by Service 2 to Kafka (I think
this is a KTable?). The job from Service 1 and the definition from Service 2 get joined together
to create a "bill of materials" that the user needs to fulfill. Service 3, a REST API, needs
to pull any unfulfilled bills for a given user. Ideally we want the bill to contain the most
current version of the job definition at the point it is retrieved (vs the version at the
point that the job assignment was published). Then, as the user fulfills the items, we update
the bill with their responses. Once the bill is complete it gets pushed on to the one or more
additional services (all basic consumers).

The part I'm having the most trouble with is the retrieval of bills for a user in Service
3. I got this idea in my head that because Kafka is effectively a storage system there was
a(n at least fairly) straightforward way of querying out messages that were keyed/tagged a
certain way (i.e., with the user ID), but it's not clear to me if and how that works in practice.
I'm very new to the idea of streaming and so I think a lot of the issue is that I'm trying
to force foreign concepts (the non-streaming way I'm used to doing things) in to the streaming
paradigm. Any help is appreciated!

Thanks very much for your kind attention!

Simon Calvin

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