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Questions tagged [event]

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Dispatching an event in the decorator or use some other design pattern entirely?

Disclaimer: before explaining the problem here I am aware that the answer to the question might be a subject of an opinion. The reason I am asking this question is because I still believe that there ...
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0 votes
2 answers
52 views

How do event sourcing services recreate the state of an entity?

I'm reading about event sourcing and have a question regarding the recreation of an entity state. For a simple scenario, lets say we have Order events such as OrderCreated / OrderUpdated / ...
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1 vote
1 answer
140 views

Event bus vs PubSub

I have been using queues and PubSub patterns for years but never really came across the terminology "event bus". After some googling I didn't really find a clear distinction between "...
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3 answers
179 views

Should I send the current or previous state with my state changed event?

I have an event that is raised when my job objects change state (e.g. initializing, running, complete, etc). The event is to be invoked from my set method in the State property, but before I make it ...
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7 votes
3 answers
2k views

How do desktop applications get notified of events over the internet?

I would like to display something on my desktop by tapping a button on my mobile app. For example, there is a "show cat" button on my mobile app. When I tap that button, a new window should ...
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3 votes
4 answers
456 views

C# How to avoid memory leak in this case

I've got a Window, which gets a viewmodel instance injected into its constructor. The window sets its DataContext to that viewmodel. The viewmodel contains a command to "submit" the window ...
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0 votes
2 answers
90 views

Scaled services and order of events sent as messages (using a broker)

How would you go about making sure that "events" sent as messages to any sort of broker (Kafka, RabbitMQ etc) from multiple instances of the same service (load balanced) are actually added ...
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  • 193
0 votes
1 answer
53 views

Long-running jobs in an event-driven environment with constrained max-execution-duration

Hello we have an async event-driven system (kotlin, spring cloud stream, rabbitmq) where there might be an event FooPayloadArrived, published by an ingress rest-controller. Processing this ...
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  • 115
-1 votes
2 answers
55 views

Applications interested to the same event and concurrency

I have an event pubblished in a bus(rabbit) and two application that are subscribed to this Event. public class CreationEvent { public int CreationEventID {get; set; } ... other properties } ...
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-2 votes
1 answer
39 views

What is the proper diagram to describe an event subscriber final graph?

I'm working on a microservice application and I need to describe the complete execution graph of a specific event being published, where each node in the graph is a specific microservice subscription ...
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3 votes
3 answers
151 views

Coping with lack of infinite retention event broker in event driven architecture

I am reading “Building Event Driven Microservices”. It states a requirement of the event broker is: Infinite retention: Event streams must be able to retain events for an infinite period of time. ...
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  • 109
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3 answers
194 views

Ingest data from our partener : API POST vs Event Driven Architecture

I am in the process of carrying out a software architecture for my client, in fact THE HISTORY OF THE REQUIREMENT : MY PARTNER SEND cvs files via MFT to MY CLIENT , many times a day . MY CLIENT has a ...
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1 vote
1 answer
109 views

Eventing: Determine if Set of Messages has been Processed

Given a Set of messages sent to a Queue, what are good ways to determine all of the messages have been processed? Constraints: Large number of messages Other messages besides those in the Set will be ...
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  • 109
6 votes
1 answer
466 views

How to represent a loop in Event Storming?

I recently ran an Event Storming session and a scenario came up where we needed to represent a loop within the process. The events and commands needed to happen iteratively until a condition is meant ...
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0 votes
1 answer
105 views

How to deal with massively concurrent events?

I got the following interview question: Say the company has this event, where we will create a button on a website and only the first ten clicks will be accepted and win a prize. Assume that there a ...
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1 vote
1 answer
108 views

What are the best way to publish application event in a spring boot application?

My goal is to collect/publish different types of information from the application. We use Kafka for the event bus. Consider the following sample code. class UserService { public User ...
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-1 votes
1 answer
100 views

How to subscribe to collection edits happening in a different thread?

I'll be using C# for my example since this is what I am using, but the problem is sort of generic. My app code takes a collection of Foos (externally populated and edited) to do some processing, and ...
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0 votes
3 answers
700 views

How to handle data inconsistency in microservice architecture?

Let's assume we have two services - user and auth with a message broker in between. user service handles CRUD action on user entity and auth service handles authentication. When a user is created/...
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-4 votes
1 answer
198 views

How to create an Event-Driven Architecture with many external sources

I work for this Accounting company - as a Product Owner - that uses several external services (one for Contract management, another one for Accounting Demands management, a third one for Financial ...
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0 answers
51 views

Experiences with coarse grained and fine grained message designs in an ECST pattern

I am currently facing a dilemma in the design of a message oriented distributed system following an Event Carried State Transfer pattern. This is essentially a "near real time ETL" used to ...
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2 votes
1 answer
88 views

Ops in event-driven paradigm

TL;DR event-driven system seems to focus on a highlevel view of the system ("error rate is 0.5%"). How are IT operations supposed to locate and remedy individual issues in such systems? In ...
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0 answers
144 views

WPF MVVM EventAggregator Cons?

We have a wpf mvvm application with a lot of "panes". Just like the draggable panes in visual studio for example. All of these are individual usercontrols with their own viewmodels and im trying to ...
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2 votes
1 answer
1k views

When to publish domain events when handling transactions in the application service

This is something that has been bothering me for quite some time, I tried different approaches over the past year but I always come back to reflect on this, so I'll throw myself out here ! So, first ...
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  • 427
0 votes
1 answer
207 views

Message bus: should an event handler trigger other commands?

Given I have a message bus that can handle commands and events. A command handler can dispatch an event. But should an event handler be able to dispatch another command? Or should event handlers only ...
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-2 votes
2 answers
80 views

How to call the API once per event-message?

I have X number of servers in NLB listening to an event that gets published by a backend system. I am planning to develop a windows service that listens to the event and then calls an internal API. ...
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0 votes
3 answers
214 views

How to implement a chain of events on a tree's CRUD operations?

I am working on a project in which I have a tree with 4 layers and the hierarchy is like this. Customer -> Site -> Location -> Guardroom In DB each entity has its own table and the child ...
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3 votes
5 answers
1k views

How to resolve cyclic dependencies in Event-driven systems?

Consider two services (bounded contexts by DDD): Sales Billing Sales is responsible for creating orders and Billing for handling payments. Sales tracks orders and Billing holds payments: Sales ...
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2 votes
1 answer
58 views

Remove unwanted parameter from event

I've run into a common annoyance where I'll have an event that sends a parameter, but some consumers of the event don't need the parameter at all. So I wrap it in another function that decouples the ...
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0 votes
1 answer
197 views

What are differences in application architecture in frontend and backend applications?

I'm pretty experienced with developing both frontend as well as backend applications, with a variety of programming languages and frameworks. I know the problem space and concepts involved in both ...
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  • 9
5 votes
2 answers
1k views

Handle failures in Event Driven Architecture

Suppose you have a bounded context with ~30 business events and, for simplicity sake, the same number of commands like ChangeUserEmailCommand -> UserEmailChangedEvent initiated from a web UI. ...
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2 votes
2 answers
616 views

Aggregation and storage system design for user event processing?

I have a eCommerce like system which produces 5000 user events (of different kind like product search/product view/profile view) per second Now for reporting business users would like to view the ...
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  • 257
2 votes
2 answers
524 views

Error handling in an event driven system

The context I have two components A & B, which communicate through events . Components B is responsible for long running background processes and it listens to the following event: ...
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0 votes
2 answers
884 views

How to send queue messages to one queue in rabbitmq?

I want to use rabbitmq to share domains events between microservices. Due to the fact that queues are round-robin, I need to define one queue per event source and event consumer. For example, cars-ms ...
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-1 votes
2 answers
702 views

How to ensure persistence in an event-driven microservice architecture?

Right now we have a set of micro services with a client-facing gateway responsible for authentication and routing. MySQL database and RabbitMQ for the message queue. Internal services may queue up ...
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4 votes
3 answers
409 views

How to model User behaviour that can be shared between microservices in Event Driven architecture?

I have an Event Sourced system that has 3 micro services (simplified): User management - Registering a user, change password etc User account - manages debiting/crediting of the user account balance ...
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42 votes
10 answers
6k views

Applicability of Single Responsibility Principle

I recently came by a seemingly trivial architectural problem. I had a simple repository in my code that was called like this (code is in C#): var user = /* create user somehow */; _userRepository.Add(...
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  • 1,534
2 votes
1 answer
50 views

Where does the responsibility for clearing higher-level caches lie in a pyrimidal calculation system with caching at multiple levels?

I'm working on system that analyses non-trivial amounts of data. The analysis is pyramidal, in that various combine to make intermediate values, which in turn combine with each other and more inputs ...
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-3 votes
1 answer
123 views

How does event.target return the DOM object?

I read through documentation and searched on google, but couldn't find a specific answer. Currently, I have an object that subscribes to a click event. I am trying to understand how a view that ...
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0 votes
2 answers
149 views

Microservice /Soa : how to fire notification depending on the caller?

I have this two use cases in a user registration process : Case 1 : the user register an account online and the system should send him an email notification in order to confirm that his account has ...
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  • 221
2 votes
2 answers
1k views

How to deal with an event if the domain aggregate was not yet persisted?

When I call paid() on my aggregate it sets all the properties internally that need to be changed based on this action. But at this time the change has not been saved to the DB, so I can't reliably ...
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  • 461
1 vote
1 answer
72 views

Publish / Subscribe Paradigm Implementation Problems

Reading the final chapter 6 of the paper "The Many Faces of Publish/Subscribe" I stumbled across: Decoupling is a desirable property because it enforces scalability at the abstraction level,...
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  • 119
5 votes
2 answers
756 views

How can we keep sight of business flows in event driven architectures?

I am planning to set up an event driven architecture using Spring Boot apps that publish and read messages from a Kafka broker. Let's suppose it were an e-commerce application with the usual events (...
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2 votes
3 answers
211 views

How are new bounded contexts deployed, and bugs fixed, in message-driven "autonomous" microservice architectures?

I'm coming from the monolith background, using a single large relational database. From my research, many proponents of the microservice architecture favor the event-driven rather than REST driven ...
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  • 199
1 vote
1 answer
235 views

Alarming on event driven systemev

How to define overall monitoring of event-driven architecture? Each component talk to other component via events. Consumer(s) react to events within minutes to days based on use case. Each component ...
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1 vote
2 answers
1k views

Designing events in an event-driven (event sourced) architecture and managing duplication

I have been creating a POC for a part of our system but I'm finding some trouble communicating some of the ideas behind it. This takes ideas from Event Sourcing and Event Driven Architecture but ...
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  • 321
2 votes
1 answer
150 views

Unit testing EventArgs - will there be timing issues?

I am writing a small game library. I capsule the logic in my model named Block. My model Block communicates only via events to it's clients (Is this a good thing to do!?). I wrote a simple unit test ...
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2 votes
3 answers
1k views

What should a method which creates conditionally self-unsubscribing event-handlers be named?

I develop/maintain an in-house library in a growing company with about 12 other developers that write code. This library is mostly used for scripting game behavior and we have many different projects ...
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1 vote
1 answer
230 views

In microservices architecture, is it reasonable that service which emits event also listens to it?

We have a complex app which built by using multiple microservices. At a runtime, one of the microservices emits an event to initialize some maintenance process in another microservices, it's ok. But ...
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  • 208
1 vote
2 answers
294 views

Was including a keyword for events a mistake in C#?

C# has events built in with a keyword. So if you want to declare an event, you write: public event MyEventHandler SomethingHappened; It is convenient, as it does allow you to add multiple event ...
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  • 7,602
1 vote
1 answer
478 views

How to write integration tests for a distributed system highly dependant on current date and flow of time?

My team and I are trying to set up some integration tests of a distributed system that is highly dependant on the flow of time and events coming from external sources. Just to give you an idea about ...
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  • 241