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LUC #49: Unpacking Vertical Slice Architecture: Principles, Practices, and Potential

Plus, API security best practices, how terraform works, and ACID properties explained

This week’s issue brings you:


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Unpacking Vertical Slice Architecture

For many software systems, layered architectures are the foundation, organizing the system around technical layers.

However, this organization often results in low cohesion between these layers, making system enhancements and maintenance challenging.

Instead of organizing by technical constraints, what if we organized the system by the features themselves?

This would maximize coupling in a single feature and minimize coupling between unrelated features.

This is the essence of vertical slice architecture.

Understanding Vertical Slice Architecture

Vertical slice architecture (VSA) reimagines app design by organizing functionality into vertical slices instead of traditional horizontal layers.

Each "slice" in VSA is a self-contained unit that represents a single feature or a tightly interconnected group of features. It encapsulates all the necessary components, ranging from the data access layer through business logic to the user interface.

This results in increased modularity, agility, and flexibility. More on this shortly.

This is quite different from layered architecture, which sorts by technical roles. VSA more closely aligns with business functions for a closer match between development and business goals.

This strategic alignment facilitates a more intuitive mapping between the software's technical structure and the organization's business processes, making VSA particularly conducive to agile development methodologies.

Example of Vertical Slice Architecture

Visualize an e-commerce platform that integrates order processing, product browsing, and user registration.

In a VSA approach, each functionality is encapsulated into a vertical slice, complete with its dedicated UI, business logic, and direct database interactions.

This not only compartmentalizes development efforts but also ensures that each slice can independently manage its data flow, state management, and presentation logic.

As you can imagine, this structure leads to a host of benefits, from facilitating concurrent feature development to allowing for isolated testing environments and deployment pipelines for each slice. 

The modularity also enables teams to implement continuous integration and deployment (CI/CD) practices more effectively, as changes in one slice can be deployed without waiting for modifications in others to be completed.

The Upside of Vertical Slice Architecture

There are some very powerful benefits that come with VSA’s self-contained slice approach.

Enhanced maintainability

The modularity of slices in VSA simplifies feature updates, maintenance, and bug-fixing processes.

Scalability and performance

Independent scalability of slices under VSA means resources are allocated exactly where needed, optimizing performance without the overhead of scaling entire layers.

Enhanced development agility

Self-contained slices enable teams to work on different features simultaneously without stepping on each other's toes. This parallel development capability accelerates the delivery of new features and bug fixes, aligning well with continuous delivery and deployment practices.

Fault isolation

Faults are contained within individual slices, making issues easier to diagnose and resolve while mitigating system impact which enhances system reliability and uptime.

Challenges and Considerations

Virtual Slice Architecture's benefits are clear, but it's not without its hurdles.


VSA's structure can inadvertently encourage code or functionality duplication, especially in shared services like authentication.

And duplication can lead to increased maintenance overhead, increased refactoring difficulties, and other hindrances. This affects our application's complexity and potentially performance.

Preventing this duplication requires attentive management and coordination across slices.

Inter-slice communication complexity

The decoupled nature of vertical slices fosters modularity but necessitates sophisticated inter-slice communication strategies. Especially when features span multiple slices.

This scenario often leads to the implementation of API gateways or message brokers to facilitate inter-slice data exchange and synchronization. And effective orchestration of these components is crucial.

Adjustment and learning curve

Moving to VSA from a conventional layered approach involves a considerable shift in both mindset and operational practices.

To fully embrace and harness VSA's potential, teams may face a learning curve and organizational changes, such as alterations in team dynamics and structures.

Key Practices for Transitioning to VSA

Here are some best practices for a successful transition to VSA.

Defining clear boundaries

Precisely defining the scope and responsibility of each vertical slice is key.

It prevents functional overlap and ensures system coherence.

Investing in communication frameworks

A robust communication system is required for effective interactions between slices.

It makes coordination and data flow between various application components easier.

Applying domain-driven design

Applying domain-driven design principles is essential for ensuring that each slice is aligned with specified company goals.

This method offers a more structured and meaningful framework within the architecture.

Wrapping Up

Organizing all files related to a feature in a single folder may initially seem unconventional or even daunting.

However, as illustrated, this approach has significant benefits. Self-contained vertical slices not only streamline development but also align software design more closely with business objectives.

By focusing on functionality rather than technical roles, VSA fosters a more intuitive understanding of the application structure and enhances agility, making it an ideal architecture for adopting agile development methodologies.

API Security Best Practices (Recap)

The rise in API-related security breaches highlights the necessity for robust API security.

Essential techniques and best practices to improve API security include; HTTPS, rate limiting and throttling, authentication, authorization, input validation, API gateway, regular security audits, dependency management, logging and monitoring, API versioning, data encryption at rest, and access controls.

API security isn’t a nice to have; it’s a must. Following the techniques and best practices I’ve shared above will take you a long way; they are the foundations of building safe and secure APIs.

What is Terraform, and How Does it Work (Recap)

Terraform, an open-source innovation from HashiCorp, transforms infrastructure management through a high-level configuration language, enabling quick, automated deployments.

Terraform ensures secure, predictable infrastructure updates with features like:

Infrastructure as code — shifts management to code for efficiency and version control.

Execution plans — offers previews before changes, adding predictability.

Resource graph — visualizes dependencies for coherent changes.

Change automation — reduces errors by automating deployments.

Terraform is more flexible than other IaC tools like AWS CloudFormation and Ansible, supporting multiple cloud services and facilitating seamless updates between development and operations.

It enhances efficiency, predictability, and scalability, bridging the gap between development and operations.

ACID Properties Explained (Recap)

The ACID model serves as a fundamental basis for handling database transactions, encompassing the core concepts required to ensure data reliability.

ACID stands for atomicity, consistency, isolation, and durability.

Atomicity — ensures transactions are "all or nothing". Critical for maintaining data integrity preventing partial transactions that could cause inconsistencies and errors.

Consistency — ensures that every transaction changes the database from one valid state to another. It adheres to all rules and constraints.

Isolation — guarantees that each transaction behaves as if it were the only one being performed at the time. It prevents concurrent transactions from causing data anomalies.

Durability — guarantees that once a transaction is committed, it remains so. Safeguarding against data loss in system failures.

ACID principles form the backbone of database transaction integrity, enabling precise and reliable transaction management.

That wraps up this week’s issue of Level Up Coding’s newsletter!

Join us again next week where we’ll explore the top 5 use cases of Kafka, how GraphQL works, stateful vs stateless, and celebrate our 50th issue.