🔧 10 Common Software Architectural Patterns Explained

Ever wondered how large-scale enterprise systems are designed? Before embarking on major software development projects, it’s crucial to select an architecture that ensures both functionality and quality. Understanding the different architectural patterns is key to making an informed choice.

What Is an Architectural Pattern?

An architectural pattern is a general, reusable solution to a recurring problem in software architecture within a specific context. While similar to software design patterns, architectural patterns operate at a broader, system-wide level.

Below, we break down 10 common architectural patterns and their applications.

1. Layered Pattern

The layered architecture organizes the system into hierarchical layers, each with a specific responsibility. Communication flows sequentially through the layers, ensuring a clear separation of concerns.

• Presentation Layer: Responsible for user interaction, rendering interfaces, and capturing user inputs.
• Application Layer: Manages user requests, orchestrates business logic, and ensures data flow between the user interface and the core system.
• Business Logic Layer: Implements domain-specific rules, algorithms, and core operations crucial to the application.
• Data Access Layer: Handles interactions with databases or other storage systems, abstracting data persistence complexities.

Key Features:

• Each layer depends only on the layer directly below it.
• Layer responsibilities are independent, fostering modularity and maintainability.

Use Cases:

• Desktop applications like text editors or accounting tools.
• Web-based platforms such as e-commerce websites with separate UI, logic, and database tiers.

Illustration:

+-------------------+
| Presentation Layer|  (Handles user input)
+-------------------+
         |
         v
+-------------------+
| Application Layer |  (Processes user requests)
+-------------------+
         |
         v
+-------------------+
| Business Logic    |  (Implements rules and operations)
+-------------------+
         |
         v
+-------------------+
| Data Access Layer |  (Manages database interactions)
+-------------------+
         |
         v
+-------------------+
|    Database       |  (Stores data)
+-------------------+

2. Client-Server Pattern

The client-server pattern divides the system into two key entities:

• Clients: Devices or applications that request resources or services.
• Server: Centralized system or machine that processes these requests and delivers the necessary resources or results.

Detailed Workflow:

• Clients interact with the server over a network, requesting specific operations or data.
• The server processes these requests, performs computations or database queries, and returns the responses.

Key Features:

• The server acts as a single source of truth, centralizing operations and data management.
• Clients remain lightweight, handling user-facing interactions only.

Use Cases:

• Email systems, where clients send/receive emails, and the server stores and manages them.
• Banking applications where clients initiate transactions, and the server processes them.

Illustration:

+------------+    Request     +------------+
|   Client   |--------------> |   Server   |
| (User App) |                | (Backend)  |
+------------+                +------------+
                                |
                                v
                        +----------------+
                        |    Database    |
                        +----------------+

3. Master-Slave Pattern

The master-slave pattern is designed to distribute tasks and enable parallel processing:

• Master Component: Centralized entity responsible for assigning tasks to multiple slave components and aggregating results.
• Slave Components: Execute tasks independently and report the outcomes back to the master.

Detailed Workflow:

• The master delegates jobs, breaking down a complex problem into smaller chunks.
• Slaves perform computations in isolation, ensuring no interdependency between them.

Key Features:

• Enables distributed task execution.
• Facilitates high fault tolerance as failures in individual slaves don’t compromise the system.

Use Cases:

• Database replication systems, where a primary database (master) synchronizes with secondary replicas (slaves).
• Distributed computing environments like Hadoop.

Illustration:

+------------+
|   Master   |  Assigns tasks
+------------+
     /   \
    /     \
   v       v
+-----+   +-----+
|Slave|   |Slave|
| A   |   | B   |
+-----+   +-----+

4. Pipe-Filter Pattern

This pattern structures the system as a series of data processing steps (filters) connected by data channels (pipes).

Detailed Workflow:

• Input data flows through multiple filters, each performing a specific transformation or operation.
• Pipes connect filters, facilitating data transfer between them.

Key Features:

• Filters are independent and reusable, making the system highly modular.
• Pipes decouple filters, allowing filters to be added, removed, or modified with minimal impact.

Use Cases:

• Compilers, where the source code undergoes lexical analysis, syntax parsing, and code generation.
• Data processing pipelines like ETL (Extract, Transform, Load) systems.

Illustration:

Input Data ---> [Filter 1] ---> [Filter 2] ---> [Filter 3] ---> Output Data

5. Broker Pattern

The broker architecture acts as an intermediary, managing communication and service discovery in distributed systems.

Detailed Workflow:

• Clients communicate with the broker to request services.
• The broker locates the appropriate server, facilitates the interaction, and relays results back to the client.

Key Features:

• Decouples clients and servers, allowing dynamic addition and removal of services.
• Hides complexities of distributed systems from clients.

Use Cases:

• Messaging systems like Apache Kafka or RabbitMQ.
• Service-oriented architectures (SOA) and microservices.

Illustration:

       +-----------+
       |   Client  |
       +-----------+
             |
             v
      +-----------------+
      |      Broker     |
      +-----------------+
       /       |       \
      v        v        v
+---------+ +---------+ +---------+
| Server 1| | Server 2| | Server 3|
+---------+ +---------+ +---------+

6. Peer-to-Peer Pattern

In a peer-to-peer system, all nodes (peers) are equal, sharing resources and responsibilities without relying on a central authority.

Detailed Workflow:

• Each peer can act as both a client (requesting resources) and a server (providing resources).
• Communication occurs directly between peers, with no intermediary.

Key Features:

• Decentralized structure ensures high fault tolerance.
• Scales effectively as more peers join the network.

Use Cases:

• File-sharing platforms like BitTorrent.
• Blockchain systems and decentralized cryptocurrencies like Bitcoin.

Illustration:

+-------+      +-------+
| Peer A| <--> | Peer B|
+-------+      +-------+
   ^              ^
   |              |
   v              v
+-------+      +-------+
| Peer C| <--> | Peer D|
+-------+      +-------+

7. Event-Bus Pattern

The event-bus pattern is an event-driven architecture where components communicate through a central event bus.

Detailed Workflow:

• Event Sources: Publish events to the bus when specific actions occur.
• Event Bus: Distributes these events to all registered listeners.
• Event Listeners: Respond to events based on their subscriptions.

Key Features:

• Components remain loosely coupled, promoting flexibility and scalability.
• New event sources or listeners can be added without significant changes to the system.

Use Cases:

• Real-time notification systems (e.g., sports score updates, social media alerts).
• Asynchronous processing in microservices.

Illustration:

   +----------+        +---------+
   | Source 1 |       | Source 2 |
   +----------+       +----------+
         |                 |
         v                 v
   +----------------------------------+
   |            Bus                   |
   |  +----------+   +----------+     |
   |  | Channel 1|   | Channel 2|     |
   |  +----------+   +----------+     |
   +----------------------------------+
         |            \            \
         v             v            v
   +-----------+    +-----------+  +-----------+
   | Listener 1|    | Listener 2|  | Listener 3|
   +-----------+    +-----------+  +-----------+

8. Model-View-Controller (MVC) Pattern

The MVC pattern separates an application into three interconnected components to decouple user interface and logic:

• Model: Represents data and business logic. It notifies views when data changes.
• View: Displays data to the user and forwards user interactions to the controller.
• Controller: Manages user input, updates the model, and triggers view updates.

Detailed Workflow:

• User inputs are handled by the controller, which updates the model.
• Changes in the model automatically trigger updates in the view.

Key Features:

• Enables parallel development of UI and logic components.
• Promotes reusability and testability.

Use Cases:

• Web development frameworks like Angular, Django, and Ruby on Rails.
• GUI applications like desktop or mobile apps.

Illustration:

 Input Events
       |
       v
   +--------+
   |  View  | <-------------------------------+
   +--------+                                 |
       |                                      |
       | View Control                         |
       v                                      |
   +-----------+                              | update model
   | Controller|                              |
   +-----------+                              |
       |                                      |
       | Query Model                          |
       v                                      |
   +--------+                                 v
   | Model  | --------------------------------+
   +--------+

9. Blackboard Pattern

he blackboard pattern is suited for solving complex, non-linear problems by aggregating contributions from various knowledge sources.

Detailed Workflow:

• Blackboard: Centralized shared workspace for storing intermediate results and the current solution state.
• Knowledge Sources: Specialized modules that contribute expertise or solve sub-problems.
• Controller: Coordinates access to the blackboard, deciding which knowledge source operates next.

Key Features:

• Encourages collaboration between independent modules.
• Adapts dynamically to complex problem-solving requirements.

Use Cases:

• Artificial intelligence applications like speech or image recognition.
• Computational biology, such as protein structure analysis.

Illustration:

[Knowledge Source A] ---> [Blackboard] <--- [Knowledge Source B]
                                  ^
                                  |
                           [Control Component]

10. Interpreter Pattern

The interpreter pattern is designed to evaluate and execute instructions written in a predefined language or grammar.

Detailed Workflow:

• Input expressions or commands are parsed into an abstract syntax tree (AST).
• The interpreter traverses this structure, executing instructions in sequence.

Key Features:

• Facilitates runtime evaluation of commands, enabling dynamic behavior.
• Highly flexible for applications requiring user-defined scripts or queries.

Use Cases:

• SQL interpreters for database queries.
• Scripting engines in applications like game development or automation tools.

Illustration:

[Input Expression] ---> [Interpreter] ---> [Output Result]

Comparison of Architectural Patterns

The table given below summarizes the pros and cons of each architectural pattern.