Feedback: 'Unobtrusive Mode Messages'

[ddonabedian]

Feedback for 'Unobtrusive Mode Messages' https://docs.particular.net/nservicebus/messaging/unobtrusive-mode

Location in GitHub: https://github.com/Particular/docs.particular.net/blob/master/nservicebus/messaging/unobtrusive-mode.md

"This is not a big deal for commands because they are always used within the boundary of a single service, and it's fair to require a service to use the same version of NServiceBus."

This remark seems to contradict this page http://docs.particular.net/tutorials/nservicebus-step-by-step/4-publishing-events/

Commands : Logical Senders = One or more

[ngallegos]

Hi @ddonabedian,

We took a look at this and do not think there is a contradiction.

The first article about unobtrusive mode refers to a logical service, or a group of endpoints.

The second article about publishing events refers to the fact that a command can be sent from one or more logical senders.

[ddonabedian]

Hi Nick,
Your reply actually confirms the contradiction.
You say "a command can be sent from one or more logical senders" but the unobtrusive mode article states commands are always used within the boundary of a single service. These two statements cannot both be true.
If multiple logical senders from different services can send the same command, then the version coupling problem exists for commands just as it does for events.

[bording]

Hi @ddonabedian,

If multiple logical senders from different services can send the same command,

That's not what the documentation is trying to say. It's saying that you can have multiple senders from within the same service, not from different services.

When talking about services design and service boundaries, commands are only sent to endpoints within a service boundary, not between services. Events are what are used to communicate between services.

The idea being conveyed in the Unobtrusive Mode page is that a single service is composed of multiple endpoints, and all of those would be maintained and deployed as single unit, where the idea of needing the same NServiceBus version would be a reasonable requirement.

We do have a free course that covers these design concepts if you want to learn more about it: https://learn.particular.net/courses/distributed-systems-design-fundamentals-online

[ddonabedian]

Hi,
Thanks for the clarification on the intended meaning. However, the tutorial itself contradicts that interpretation.
The step-by-step tutorial (Part 4) states explicitly: "A command can be sent from anywhere", and the comparison table lists "One or more" logical senders for commands with no mention of a service boundary constraint.
The example given in the tutorial is a website UI sending PlaceOrder, which is typically a separate deployable service from the Sales endpoint that handles it.
If the intent is that all command senders must reside within the same service boundary, the tutorial should say so explicitly. As written, it actively suggests the opposite.

[bording]

The tutorial is intended to teach how to use NServiceBus in an easy to follow manner. It's not trying to teach proper service oriented design concepts. That would be way too much to introduce while also learning NServiceBus.

We'll take your feedback in mind when we consider future work on the tutorial.