Request Response Messaging Pattern with MassTransit

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The definition of the Request Response pattern is: "It is a message exchange pattern in which a requestor sends a request message to a replier system, which receives and processes the request, ultimately returning a message in response." In this video, I'll show you how to implement asynchronous Request Response messaging with MassTransit and RabbitMQ.
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Chapters
0:00 What are we trying to implement?
1:15 Adding the Request Response message contracts
3:12 Sending the Request message with IRequestClient
4:45 Consuming the Request and returning the Response
9:05 Refactoring Request Response messaging to a service
11:39 Returning multiple Response message types

[@MilanJovanovicTech]

Want to master Clean Architecture? Go here: bit.ly/3PupkOJ Want to unlock Modular Monoliths? Go here: bit.ly/3SXlzSt

[@dcernach]

Great video! Please consider creating a series of videos about MassTransit, with a focus on topics like State Machines, Routing Slips, and more. MassTransit is a fantastic library to be used within microservices!

[@MilanJovanovicTech]

I already have a few about MassTransit, but I'll happily do more

[@nove1398]

I would like to see these as well

[@ferdikosasih]

Hi have you ever compared with cap library? What the differences

[@rezvlt9285]

You always make the videos I most need. Thank you !

[@MilanJovanovicTech]

I have a hunch for that 😁

[@michaelreiners8437]

Thanks a lot! Exactly what I just needed :)

[@MilanJovanovicTech]

You're welcome! :)

[@GeoffSeeley]

You should probably handle timeouts for Requests as well because there is no guarantee you'll get a Response. This is one of the fun things about Event driven systems 🙂

[@MilanJovanovicTech]

The default timeout is 30s. If it takes more than that to get a response, you probably shouldn't be doing request-response anyway. But I agree that it should be handle in some way

[@mohamedalaa8212]

great video! How about making your next one on Circuit Breakers or Bulkhead pattern or more on MassTransit ? I'm sure it would be awesome

[@MilanJovanovicTech]

Great ideas!

[@KenzoArts]

Hello Milan, Would you please consider making a course about Microservices? I love so much your videos !

[@MilanJovanovicTech]

It will happen at some point :)

[@PhobiaQQ]

great video, but I could not find this pattern described in MassTransit documentation. It's a pity you missed a part how you set up a message broker here. Did you use separate queue for request/response? Also I found that request/response is async pattern for http communication, while request/reply is async messaging pattern

[@MilanJovanovicTech]

Here: masstransit.io/documentation/concepts/requests

[@renatogomes3457]

Hi Milan, awesome content as always! Is it a good practice to completely remove the use of MediatR and switch to Request/Response with MassTransit (InMemory, perhaps)? I'm a bit confused, but don't both serve the same purpose? Could you please provide some insights on this? Thank you very much.

[@MilanJovanovicTech]

Consider the ease of use with both libraries. MediatR is much simpler to configure and use than MassTransit. If all I need is an in-memory bus, MediatR is still a great choice

[@pilotboba]

imnsho Mediatr is for intraprocess messaging. Masstransit / Rebus are for interprocess messaging.

[@guilhermebley4001]

Great video. One doubt, when we use AsNoTracking in EF, we need to call it at beggining or end of query?

[@MilanJovanovicTech]

It won't matter.

[@user-fj6js6px6f]

What is benefits of using RabbitMq instead of http is this case? It looks like synchronous way of communicating

[@akashkarve1991]

Http is synchronous, rabbit mq request-response is async

[@MilanJovanovicTech]

It looks like it's synchronous because the caller has to "block" and wait for a response. But the benefit is that the services don't have to know about each other - unlike with HTTP. You need to know which API to call and where to find it.

[@musazulu7013]

Excellent video @MilanJonovicTech, is it possible to get a tutorial about Kafka

[@PhatBoyG]

I have an entire series on Kafka with MassTransit: kzbin.info/aero/PLx8uyNNs1ri0RJ3hqwcDze6yAkrmK1QI5

[@MilanJovanovicTech]

Chris stealing the show 😁

[@n.sharma5810]

Hi Milan, if possible please create a small project explains microservice architecture completely

[@MilanJovanovicTech]

A small project can't explain that

[@muhammadtariq8323]

I requested you that make a video on .NET Core, static file response compression. Pre-Compress (br / gzip) or run time by .NET Core or IIS. Which are best and how to implement

[@MilanJovanovicTech]

Ok

[@muhammadtariq8323]

@@MilanJovanovicTech thanks 👍

[@thedacian123]

How did you registered in the DI container IRequestClient?

[@MilanJovanovicTech]

You don't have to, it's automatically registered

[@user-xm7sh3vw8o]

MassTransit+RabbitMq ，The consumer fails and can be put into the standby queue. What needs to be done?

[@MilanJovanovicTech]

Handle the error on the request client side

[@nomad191]

Great Video. Where can I download the source code for this?

[@MilanJovanovicTech]

Hi, I share the source code on Patreon

[@coderider3022]

How does it correlate response properly , doesn’t seem to enable sessions on a queue?

[@MilanJovanovicTech]

Attaches a message ID

[@giorgigiorgobiani9547]

Hello Milan, i use this request/response pattern with rabbitMQ, but sometimes i have an issue: when api B is in idle state (not recieving requests) rabbitMQ connection of api B is lost and when i send reqeust from api A with requestClinet i get timeoutexception. is there some method to overcome this issue?

[@MilanJovanovicTech]

Nope. That's called temporal coupling. In request-response we assume the other side is always available. But that might not always be the case.

[@giorgigiorgobiani9547]

@@MilanJovanovicTech ok but is there a way keep other side always available..to configure rabbitMQ connection to be all the time alive while api running..do u know such thing? If not, what is solution ..

[@balajisairamnarasimhan]

Can we use mass transit if we are making this cloud native microservices ? Benefit of using mass transit ?

[@jeroen7362]

the benefit of MT is that you are decoupled from the transport/bustype. so locally you can run rabbit, or even rabbit in a docker. and in the cloud you use azure servicebus or other cloud bus. in unittest you can run in memory bus. your code is transport agnostic, only in the startup of the bus you need to start one bustype depending on an appsetting.

[@balajisairamnarasimhan]

@@jeroen7362 thanks a lot

[@MilanJovanovicTech]

You absolutely can

[@balajisairamnarasimhan]

@@MilanJovanovicTech thanks Milan so can you guide me the steps for that ? Or does it work internally as a container ?

[@makemeafirewall]

The reason you said you register the ArticleViewsService as scoped is because IRequestClient is also scoped, how is it possible to generally check by DI container and the dependency chain to make sure I don't do anything funny in the registration I wasn't supposed to do? Is there a tool to see all the DI chain or the places where things are not using the same registration type?

[@jeroen7362]

if you use the built in DI you will find out for sure without tools, when a singleton tries to use a scoped service. the other way around is perfectly fine. You can use scoped services in a singleton by creating a scope around it.

[@makemeafirewall]

@@jeroen7362 what happens when a singleton tried to use a scoped service without creating a scope? Do I get an error? Always?

[@makemeafirewall]

@@jeroen7362 we had an issue with the DB context that was used by a singleton and we changed it to be transient to solve the problem, don't exactly remember. I wanted a tool that shows me the dependency tree to find these errors if I suspect I did something wrong with the service registration.

[@jeroen7362]

@@makemeafirewall as far as i have experienced it will always throw a runtime exception like "Cannot consume scoped service from singleton" This would usually only happen during development if you even touch the appservice in your debug session.

[@makemeafirewall]

@@jeroen7362 i think it gets more complicated when a transient is injected with a scoped or the other way around. There should be a way to get the tree and search it, also it would be great to see the request pipeline because sometimes the project is already running in production and you are not always aware of the order of things, especially handlers that are used or even registered using reflection

[@GamalSherbiny]

what advantage does this solution have over http request response?

[@MilanJovanovicTech]

You don't need to know the address of the other service - only the message contract. This can be a big advantage. The downside is increased latency, as we're passing around more messages.

[@hanoguzakpinar]

is there any way to use exchange names for publisher?

[@MilanJovanovicTech]

MassTransit routes this to an exchange under the hood. I'm sure it's possible to configure it explicitly, but you should check the docs.

[@raghavendrahabbu]

Where can I get complete source code?

[@MilanJovanovicTech]

Patreon: www.patreon.com/milanjovanovic

[@BlueLabel1980]

Github for this expample?

[@MilanJovanovicTech]

I share the source code on Patreon

[@amitkumdixit]

Don't see any added benefit in this use case. One more failure point in the response cycle.

[@MilanJovanovicTech]

Anything can fail in distributed systems, I don't see that as a counter point

[@DjDanny32]

MassTransit + RabbitMQ adds many benefits. For example, imagine your dB is down. Rabbit will retry your request (within your defined parameters) for you

[@techpc5453]

[@MilanJovanovicTech]

👋

[@srik790]

But I guess the UI composition technique is better in this scenario.

[@MilanJovanovicTech]

Perhaps

[@srik790]

@@MilanJovanovicTech Any plans to cover UI composition in your videos?

[@haraheiquedossantos4283]

By the way I agree with the comment below, like using some BFF to orchestrate. And I think messaging Request-Response pattern is better suited to workflows long running business process that span multiple boundaries when we are dealing with sagas. Don't you agree?