Questions tagged [event]

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77 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 ...
4
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2answers
357 views

Domain Events Grouping/Buffering

Suppose I have 3 domain events, Event1 Event2 and Event3. When command arrives at my Service Layer, I can rise 2 commands at the same time - e.g. Event1 and Event2. One Class has event listener for ...
2
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2answers
303 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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3answers
157 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 ...
0
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1answer
566 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 ...
1
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1answer
70 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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3answers
152 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 ...
5
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1answer
257 views

Event Storming: How to represent a loop?

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 ...
1
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1answer
208 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 ...
0
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1answer
84 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 ...
2
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1answer
71 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 ...
5
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4answers
44k views

Detect or Prevent Screen Capture Applications

I am building an app that displays very sensitive information and as such, I want to be able to either Disable the ability to capture the screen Redact the portion of my app that is on the screen ...
1
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1answer
142 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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3answers
402 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/...
-4
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1answer
116 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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0answers
29 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 ...
2
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1answer
79 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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0answers
107 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 ...
2
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1answer
609 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 ...
0
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1answer
102 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 ...
4
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2answers
772 views

Data persistence for transactional customer emails

I'm developing a system to handle sending transactional emails to our customers. This is how it works: An event occurs during the order's life cycle, for example 'shipped' This event will trigger ...
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2answers
77 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. ...
3
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4answers
627 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 ...
2
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1answer
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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1answer
110 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 ...
5
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2answers
991 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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2answers
648 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 ...
2
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2answers
403 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: ...
4
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3answers
344 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 ...
42
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10answers
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(...
2
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1answer
49 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 ...
2
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2answers
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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1answer
93 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 ...
2
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3answers
942 views

Performance increase by only attach onblur handler inside of onfocus handler?

Given a web page with input fields, does it have a performance difference whether or not you assign the onblur handler inside of the onfocus handler like so: var inputFields = document....
0
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2answers
134 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 ...
1
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1answer
68 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,...
5
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2answers
629 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 (...
2
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3answers
195 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 ...
3
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2answers
3k views

Combining asynchronous and synchronous programming

I've got trouble wrapping my head around a certain problem: In my data-flow app (a visual editor), I have both autonomous objects which communicate though ports via unordered simultaneous messages ...
22
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3answers
13k views

DDD: Where to place domain event handlers?

Could you tell me your opinion that which layer is the right one to place domain event handlers in DDD? For example, I have application service to add a new contract and I'd like to send an email ...
2
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3answers
807 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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2answers
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 ...
20
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3answers
7k views

API Gateway (REST) + Event-Driven Microservices

I have a bunch of microservices whose functionality I expose through a REST API according to the API Gateway pattern. As these microservices are Spring Boot applications, I am using Spring AMQP to ...
1
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1answer
216 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 ...
1
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2answers
281 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 ...
1
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1answer
437 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 ...
1
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1answer
2k views

Event Sourcing and cross Aggregate validation

I am looking into Event Sourcing (ES) and having a play around with some code Greg Young put together (Greg Young Git Repo). I like what ES offers in terms of functionality, but I am trying to apply ...
3
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2answers
157 views

Is avoiding raising an event when it is not needed considered premature optimisation?

I have a custom TextBox that validates its input. Whenever the validity of the input changes, a ValidityChanged event is raised and the user is informed about the validation results. My question is ...
2
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2answers
1k views

How chose a design for an event system

I'm working on a Entity Component System for learning purpose. I made major changes with my design so I was wondering if I could pick a better design for my event system. The purpose of the event ...
0
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1answer
167 views

For what reasons would you use AngularJS expression (&) binding instead of using events?

Like the title asks, for what reasons would you use the ampersand binding in AngularJS instead of utilizing an event system--especially in a case where your application already uses events for some ...