Sagas: Event Choreography & Orchestration (NServiceBus) 

It's not an either/or with Choreography & Orchestration. You can use both in your system in different places. Where do you use Choreography & Orchestration?

I had to deal with this a while ago. We had a critical choreography process a while ago that was giving us headaches. We managed to catch fresh hair and caught up to business demands, so we had time to refactor. We ditched the choreography for an orchestrator because it was becoming too difficult having to add new consumers if anything new came up, our new orchestration (or orchestrator) is the AWS Step Functions service. Night and day.

I think this is first video I came across which kind of explained the difference between command & events so beautifully. thanks !!

Thanks for the video! I would add that BPMN-based orchestrators can significantly help in complex business scenarios despite of they introduce some sort of coupling. Being able to see what's going on in the system from one central perspective is very helpful.

HI Derek. I am watching all your videos, thanks a lot to share this with us. Kind Regards from Argentina, Buenos Aires !!

Tremendous video! Very well explained! Thanks!

Clear explanation. Thanks

Thank you alot!

Would love to get your take on routing slip choreography with MassTransit and/or NServiceBus. Keep up the great work.

Hello, very informative and clean video, especially for beginners. Although I have stumped upon a problem, comparing to scenario from video (I like the last mixed approach very much, so let's focus on that): Let's say there is an Order Delete command (not the NServiceBus one) genereted by the user, order get's deleted which is an aggregate, order deleted event added to the queue with an outbox pattern, context is saved and order deleted event is published (the bussines logic doesnt makes sens in this example, but just hipoteticly). Then billing reacts with deleting some data in it's own context, which is succesfull and some blilling deleted event is published, but warehause buisness logic would result in publishing compensating event. Yet there is no way of restoring a deleted aggregate from Sales or changes made by performing a delete in billing context, because I have only some minor data in the events which are POCO objects or just only the ids. What to do in is this kind of situation, is there other way to approach this then 2PC? I thought about setting some flag IsDeleted, global filters and some background service to delete those with a flag once in a while, but what if the background service will performe cleanup when the order delete workflow is being processed? and also this seems like a overcomplicated solution and whatever approach I pick results in inconsistent data needing manual intervention. Would be very gratefull for any guidelines, thanks in advance.

Thanks for video. What do you think about workflow tools , for example using temporal.io or AWS step functions to orchestrate business processes?

Very useful piece. Thank you.👍

when would you use choreography vs orchestration? and how do they relate to the "saga"?

If the user should receive a notification or email for one or more of the events, would this be the place to also initiate sending such messages?

Cool, good to know that orchestrator that I found in project isn't doing what it's supposed to be doin.

Do you sometimes store the current state in a database? I'm not using .net so I don't know if changing `Data` does something behind the scenes. Thank you for all your videos

Great tutorial ! Do you have a playlist of all the microservices related stuff ?

Hi Derek, thank you very much for this video! Have some questions, would be great if you can answer. What you think about totally separated Orchestration in separated service (not "coupled" to Order Service side)? Would be that a good approach? Another thing, if we are using Orchestration with the NServiceBus and for example, Bill Service "calls" Warehouse Service (via commands through Orchestrator), what happens if Warehouse Service is down or something similiar? How should we handle this situation? Thank you!

Can you explain the distinct differences between a Saga Orchestrator and a Process Manager? I am confused by how similar they seem to be and how different people whose articles/videos I am watching define them differently. Does a Process Manager , itself , manage the state of the service , whereas as an Orchestrator merely manage which messages to respond to a service based on the message it receives from a specific service? Basically, Stateful (Process Manager) vs Stateless (Saga)? As well would a Saga Orchestrator be asynchronous vs a Process Manager which would be synchronous?

Awesome article! To keep it simple In orchestration approach, Is it ok to not to use/publish message/events to invoke subsequent services instead make a http calls. Would you mind to guide the pros and cons of it!

Let's say we have orchestration with five events/commands. On initial command, we want to pass data that's required by last one. Basically, we have to drag data through all events until it reaches last event. How would you solve this issue? Maybe storing data somewhere else instead of passing through each event?

Hello, Thanks for the video! I am wondering if the Events Handled by Saga are created only for the Saga Orchestration purpose. IE: Suppose that, in your example, we have received a CreateShippingLabel event from other part of our application (that is not the saga), How saga should ignore this event?

Do Micoservices have a get request? Cause if they do its not autonomy. I created a order sage to create a order but what if the customer needs to retrieve that order after creating it. 🤷🏾‍♂️ should I create a different service to aggregate customer orders. Whats your opinion thank you.

An orchestrator is nothing but a good ol'' Actor model. TIL.

In orchestration case, event and command triggered by same event will usually have same attributes. Take OrderPlaced event BillOrder command as example. They both have OrderId integer. Now imaging there are more attributes, you'd have to literaly copy-paste objects all the time. Any suggestions how to overcome that?

Im quite confused about async way of sending events. which means one event can be sent without waiting for the other events to complete? or async in relation to other codes that are being processed, since it's not logical to process shipping when billing is not done yet. what does it mean Derek? thanks

Hi, I would like to know if makes sense to use Saga with Kafka. The idea is to create a topic to getting all streams named as topic_orchestrator and one consumer to deal with Saga. I would like to get your opinion.

Is the advantage of Orchestration that now services don't have to listen to both Events _and_ Commands? (like the [Sales] services is having to do in the Choreography example) I.e. *Choreography* Services: Events + Commands in, Events out *Orchestration* Services: Commands in, Events out Orchestrator: Events in, Commands out *Edit:* How would either pattern handle commands that require a response. E.g. A `ViewOrder` command?

after complete process how to send response to users? it's async but user need to get response after request.

Can you do it with masstransit?

Thanks for sharing. I can't see how Choreography-based saga is decoupled, let me explain. Event based communication is decoupled because when Order Service publishes OrderCreated event, it has no expectation about any of it's listener, it doesn't even care if there is any listener at all, that is fundamental property of decoupled communication. With Choreography-based saga, you DO EXPECT a response from an event which you published (Either success event, like ShippingLabelCreated, or failure event, like BillingFailed). That is not a decoupled communication by any definition i'm aware of, that is just Request/Response (not the HTTP based, but message based via Reply of NSB for example) model done via events. Business transaction by definition implies the coupling between the participants, because of atomicity, you want all of them or none of them, this coupling cannot be hidden or eliminated and Orchestation-based saga is a clear example of that, it's just playing with word "Event".

What happens if the warehouse throws an exception