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What is the difference between MVC, MVP, MVI, MVVM, MVVM-C, and VIPER architecture patterns?
This week’s issue brings to you the following:
MVC, MVP, MVI, MVVM, and VIPER architecture patterns
How Shopify Builds a Resilient Payment System
How Does OAuth 2.0 Work
Bonus: Cloud Databases Cheat Sheet
So, let’s dive in.
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Architecture patterns are blueprints for structuring software applications. They abstract solutions to common issues, ensuring efficiency, scalability, and maintainability.
Here is the list of the most essential architectural patterns:
It is one of the earliest and most adopted design patterns. Its primary goal is to separate the application's data, user interface, and control logic into three interconnected components.
Here, the Model manages data and logic, the View displays the information, and the controller connects the Model and View, handling user input.
Usage: For Web applications with a clear separation between data handling and UI.
The pattern evolved from MVC, aiming to address its shortcomings in event-driven environments by decoupling the View from the Model, with the Presenter acting as a middleman.
Here, the Model manages data, views display data, and sends user commands to the Presenter, while the Presenter retrieves data from the Model and presents it to the View.
Usage: Applications emphasizing testing and UI logic, such as Android apps.
MVI is a reactive architecture embracing unidirectional data flow, ensuring that, given a state, the UI remains consistent.
Here, the Model represents the state, View reflects the state, while intent represents user actions that change the state.
Usage: Reactive applications or frameworks like RxJava with a focus on state consistency.
MVVM arose to address complexities in UI development, promoting a decoupled approach with the ViewModel handling view logic without knowing the UI components.
Here, the Model manages and displays data, while ViewModel holds and contains UI-related data.
Usage: UI-rich applications or platforms with data-binding, such as WPF or Android with LiveData.
MVVM-C (MVVM with Coordinator)
MVVM-C builds upon MVVM, introducing the Coordinator to handle navigation, decoupling it from View and ViewModel.
Usage: larger applications, especially iOS, where complex navigation needs separation from view logic.
VIPER is a modular architecture akin to Clean Architecture. It emphasizes testability and the Single Responsibility Principle by breaking down application logic into distinct components.
Here, the View displays what the Presenter sends, the interactor contains business logic per use case, the Presenter contains view logic for preparing content, the entity includes a primary model object, and the router contains navigation logic.
Usage: Complex applications, especially iOS, need modularity, testability, and clarity.
Building a Resilient Payment System by Shopify
The recent article by Shopify Engineering explained the top 10 most valuable tips and tricks for building resilient payment systems.
Here is the list:
Lower your timeouts
They suggest investigating and setting low timeouts everywhere possible. For instance, Ruby's built-in Net::HTTP client has a default timeout of 60 seconds to open a connection, write data, and read a response. This is too long for online applications where a user is waiting. The author suggests an open timeout of one second with a write and read or query timeout of five seconds as a starting point.
Install Circuit Breakers
Circuit breakers, like Shopify's Semian, protect services by raising an exception once a service is detected as being down. This saves resources by not waiting for another timeout. Semian protects Net::HTTP, MySQL, Redis, and gRPC services with a circuit breaker in Ruby.
The author discusses Little's Law, which states that the average number of customers in a system equals their average arrival rate multiplied by their average time. Understanding this relationship between queue size, throughput, and latency can help design systems that can handle load efficiently.
Add Monitoring and Alerting
Google's site reliability engineering (SRE) book lists four golden signals a user-facing system should be monitored for latency, traffic, errors, and saturation. Monitoring these metrics can help identify when a system is at risk of going down due to overload.
Implement Structured Logging
They recommend using structured logging in a machine-readable format, like key=value pairs or JSON, which allows log aggregation systems to parse and index the data. Passing along a correlation identifier to understand what happened inside a single web request or background job is beneficial in distributed systems.
Use Idempotency Keys
To ensure payment or refund happens precisely once, they recommend using Idempotency keys, which track attempts and provide only a single request sent to financial partners. This can be achieved by sending a unique idempotency key for each shot.
Be Consistent With Reconciliation
Reconciliation ensures that records are consistent with those of financial partners. Any discrepancies are recorded and automatically remediated where possible. This process helps maintain accurate records for tax purposes and generate accurate merchant reports.
Incorporate Load Testing
Regular load testing helps test systems' limits and protection mechanisms by simulating large-volume flash sales. Shopify uses scriptable load balancers to throttle the number of checkouts happening at any time.
Get on Top of Incident Management
Shopify uses a Slack bot to manage incidents, with roles for coordinating the incident, public communication, and restoring stability. This process starts when the on-call service owners get paged, either by an automatic alert based on monitoring or by hand, if someone notices a problem.
Organize Incident Retrospectives
Retrospective meetings are held within a week after an incident to understand what happened, correct incorrect assumptions, and prevent the same thing from happening again. This is a crucial step in learning from failures and improving system resilience.
How Does OAuth 2.0 Work
OAuth 2.0 is an authorization framework that standardizes the process for third-party applications to securely get access to an HTTP service on behalf of a user.
The framework defines four roles:
Client: The application requesting access to resources.
Resource Owner: The user who can grant or deny access to their data.
Resource Server: Houses the protected user data. The client wants data from here.
Authorization Server: Authenticates the resource owner, then issues access tokens to the client.
The process usually goes like this:
1. The user wants to access some resources in the app
2. The app requests authorization
3. User input credentials
4. App transfer credentials with OAuth keys to the Authorization Server
5. The authorization server returns the Access token
6. The app sends the access token to the resource server
7. The resource server serves the resource to the application
8. The app returns info to the user that the app is accessible
OAuth allows different flows (processes), such as:
Authorization Code Flow - To be used for server-side applications, it acquires an authorization code to exchange for an access token, ensuring the client never exposes the tokens to the user-agent.
Implicit Flow - Previously used for client-side applications like SPAs, it directly returns an access token upon authorization but lacks refresh tokens and is less recommended due to security issues. It is deprecated due to security weaknesses.
Resource Owner Password Credentials Flow - This flow allows the client to use the resource owner's username and password directly, suitable for highly trusted or legacy applications, but is discouraged due to security risks.
Client Credentials Flow - For server-to-server authentication, a client can use its credentials instead of impersonating a user to obtain an access token.
Refresh Token Flow - When an access token expires, the client can obtain a new token using a refresh token without requiring user interaction.
Device Code Flow - Designed for devices with limited input capabilities, it involves the user authorizing the device on a secondary device, following which the primary device gets the access token.
Extension Flow - A catch-all for custom flows, allowing for adaptations of the OAuth 2.0 protocol to cater to specific needs or scenarios not covered by other predefined flows.
Usually, use cases for OAuth 2.0 usage are:
Third-Party Access - Users can grant third-party applications limited access to their resources without sharing their credentials, like allowing a photo printing service access to photos stored in a cloud service.
For example, A user allows a scheduling app to access their Google Calendar to automatically set up meetings without sharing their Google credentials.
Single Sign-On (SSO) - It facilitates Single Sign-On (SSO), where users can log in to multiple services using a single ID, streamlining the authentication process across platforms and services.
For example, An employee logs into their corporate network and can access different departmental applications like email, HR system, and project management tool without logging in again.
Mobile Applications - OAuth 2.0 provides a framework for mobile apps to obtain the necessary tokens for accessing protected resources, ensuring secure operations.
For example, A user downloads a fitness app which, upon authorization via OAuth 2.0, accesses their Spotify playlists to play music during workouts without requiring separate logins.
This approach has some cons, too. Implementing OAuth 2.0 can be complex, especially for developers unfamiliar with its concepts and flows. While OAuth 2.0 is designed for authorization, it’s sometimes mistaken for an authentication protocol, which it's not. This misconception can lead to improper implementations and potential security risks. Also, the specification leaves room for interpretation, leading to inconsistent implementations across different service providers, which can cause interoperability issues.
Bonus: Cloud Databases Cheat Sheet
Check out this helpful cheat sheet for different kinds of database types:
Relational - Traditional applications, ERP, CRM, e-commerce.
Key-Value - High-traffic web applications, e-commerce systems, and gaming applications.
In-memory - Caching, session management, gaming leaderboards, geospatial applications.
Document - Content management, catalogs, user profiles.
Wide-column - High-scale industrial applications for equipment maintenance, fleet management, and route optimization.
Graph - Fraud detection, social networking, recommendation engines.
Time-series - Internet of Things (IoT) applications, DevOps, industrial telemetry.
Download the cheat sheet in the PDF version.
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