Decomposing Monolithic Applications and Converting them to Microservices: Do You Have the Necessary Skills?

Begin by identifying reusable components within a monolithic application and then mapping them to microservices. This will typically involve an expert analysis of existing codebase to identify common functionalities that can be extracted and reused as independent services. Below is a step-by-step guide on how to approach this process:

Two Key Aspects of Decomposition

• Codebase Analysis:

 Conduct a thorough analysis of the monolithic application's codebase.

 Understand the different modules, classes, and functions within the application.

• Identify Common Functionalities:

 Look for patterns and repetitions in the code.

 Identify functionalities that are used in multiple parts of the application.

The First Three Steps: An Example Scenario

• Identify Reusable Components: Authentication Service

 Authentication logic is used across multiple parts of the monolithic application.

• Decompose the Application Component

 Create a separate microservice for authentication.

 Define APIs: /login, /register, /reset-password, etc.

• Implement and Refactor

 Develop the Authentication Service.

 Refactor monolithic code to call Authentication Service APIs.

Build APIs for Different Reusable Components

1. Reusable Authentication Service

Extract authentication and authorization logic into a separate microservice.

Define APIs for user login, registration, password reset, etc.

2. Reusable Email Notification Service

Create a microservice for sending email notifications.

Define APIs for triggering and sending various types of emails.

3. Reusable Data Access Service

Extract data access and CRUD operations into a separate microservice.

Define APIs for interacting with common data entities.

How to Identify Reusable Components?

1. Common Modules or Libraries

Look for modules or libraries that are used across different features.

These could be utility functions, data access layers, validation logic, etc.

2. Business Logic

Identify business rules and logic that are applicable to multiple parts of the application.

Common algorithms, calculations, or decision-making processes can be potential candidates for reuse.

3. Shared Data Models

Examine data models and entities that are shared across different functionalities.

Consider extracting these data models as reusable components.

4. External Integrations

Components that interact with external systems or APIs in similar ways can be candidates for reuse.

For example, authentication mechanisms, payment gateways, or email notification services.

How to Define Reusable Microservices?

1. Decompose Common Functionalities

Break down identified reusable components into smaller, focused microservices.

Each microservice should encapsulate a specific set of functionalities.

2. Define Interfaces

Design clear interfaces (APIs) for each microservice.

Determine how other parts of the application or external services will interact with these microservices.

3. Service Contracts

Specify contracts for communication between microservices.

Define input/output formats, data structures, and protocols.

Identify Bounded Contexts that can be Used to Build More Microservices

1. Use the Context Mapping

Look for areas of the application where specific business rules, data models, and processes apply.

2. Ubiquitous Language

Define a common, shared language (Ubiquitous Language) that is used consistently across the application.

Use this language to identify boundaries between different business contexts.

3. Separation Criteria

Look for points of change: Where are requirements likely to change independently of other parts?

Identify areas with different data models, rules, or constraints.

Example Scenario

For an e-commerce platform, potential bounded contexts could be User Management, Product Catalog, Order Processing, and Payment Processing.

Map Bounded Contexts to Microservices

1. Functional Decomposition

Break down each bounded context into specific functionalities or capabilities.

Each microservice should have a well-defined responsibility related to its bounded context.

2. Data Ownership

Determine which microservice will own and manage specific sets of data.

Define how data will be shared between microservices if needed.

3. Example of Mapping

User Management Bounded Context ➡️ User Management Microservice

Product Catalog Bounded Context ➡️ Product Catalog Microservice

Order Processing Bounded Context ➡️ Order Processing Microservice

Payment Processing Bounded Context ➡️ Payment Processing Microservice

Define Interfaces and Contracts

1. API Design

Define clear interfaces (APIs) for each microservice.

Use RESTful APIs, GraphQL, or other appropriate protocols for communication.

2. Service Contracts

Specify contracts for communication between microservices.

Define input/output formats, data structures, and protocols.

3. Event-Driven Architecture (Optional)

Consider using events for asynchronous communication between microservices.

Events can represent domain events like "OrderPlaced" or "PaymentProcessed".

Know Why Configuring Reusable Components in Microservices Requires Code Refactoring

Reusable components in microservices often require refactoring for several reasons. When transitioning from a monolithic application to a microservices architecture, the structure, dependencies, and design patterns need to be adjusted to fit the new distributed nature of the system. Here's why reusable components in microservices typically require refactoring:

1. Decomposition from Monolithic Code

• Reusable components in microservices are often extracted from existing monolithic codebases.

• The code in a monolith is designed to work within the context of a single, cohesive application.

• Refactoring is necessary to break down the monolithic code into smaller, more focused services.

2. Boundary Definitions

• Microservices are defined by clear boundaries that encapsulate specific business capabilities.

• Refactoring helps define these boundaries for each microservice, ensuring that each service has a well-defined responsibility.

• This involves restructuring code, moving functionalities, and defining clear interfaces.

3. Isolation and Independence

• Microservices should be self-contained and independent.

• Refactoring ensures that a reusable component is isolated from other parts of the application and can function independently.

• Dependencies on other components or services are minimized.

4. API Design and Contracts

• Reusable components need well-defined APIs and contracts for communication.

• Refactoring involves designing and defining clear interfaces (REST APIs, GraphQL schemas, etc.) for the reusable components.

• This includes specifying input/output formats, data structures, and protocols.

5. Database Separation

• Microservices often have their own databases or data stores.

• Refactoring may involve separating the data layer from the reusable component, ensuring that the service has its own data store.

• Data access logic needs to be adjusted to work with the new data store.

6. Technology and Stack

• Microservices allow for technology flexibility, enabling teams to choose the best tools and technologies for each service.

• Refactoring involves adjusting the technology stack to suit the requirements of the reusable component.

• For example, if a monolith uses a specific database technology, the reusable component might need to be refactored to work with a different database technology.

7. Scalability and Performance

• Microservices are designed for scalability and performance.

• Refactoring ensures that the reusable component is optimized for scalability, with the ability to scale independently of other services.

• This may involve optimizing code, implementing caching strategies, or redesigning algorithms.

8. Testing and Deployment

• Reusable components need thorough testing in the context of microservices.

• Refactoring includes writing unit tests, integration tests, and end-to-end tests for the reusable component.

• Deployment strategies need to be updated to deploy the component as a microservice, possibly using containerization (Docker) and orchestration (Kubernetes).

9. Monitoring and Logging

• Microservices require robust monitoring and logging.

• Refactoring includes implementing logging and monitoring for the reusable component.

• This ensures that the service can be monitored for performance, errors, and availability.

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