Architecture Design: Sidecar Pattern Explained

Context and Questions

Modern applications usually need to provide the following common functional components for different services:

• Monitoring and logging
• Configuration Management
• Service Discovery
• Network Communication
• Safety Features

Integrating these features directly into every application can lead to the following problems:

• Code duplication: When each service attempts to handle the same functionality, a lot of duplicate code is generated, increasing the risk of inconsistency and introducing errors.
• Increased complexity: Having each service manage its own functionality makes the entire architecture more complex and difficult to maintain.
• Reduced maintainability: Shared functionality is spread across different services, making updates difficult and error-prone.
• Language/framework limitations: If services are based on different technologies, it will be difficult to implement a consistent solution.
• Difficulty in updating and modifying: Updating shared functionality often means modifying multiple services, which increases deployment complexity and increases the risk of downtime.

Solution: Sidecar pattern

The Sidecar pattern solves the above problems in the following ways:

• Deploy supporting components as independent services
• Deploy these services together with the main application (same life cycle)
• Providing a consistent interface for cross-cutting concerns
• Enable independent updates and maintenance

Key Components

Main application and sidecar

Parent/Main Application:

• Contains core business logic
• Focus on key features
• Keep it language and framework agnostic

Sidecar:

• A helper component that works together
• Dealing with cross-cutting concerns
• Provides supporting functions
• Can be independently developed and maintained
• Shares lifecycle with main application

Communication flow mode

There are two communication flows in Sidecar mode:

• Sidecar as Proxy
• Sidecar as Companion Service

Mode 1: Sidecar as a Proxy

In this mode:

• External traffic first goes through the sidecar.
• The sidecar handles cross-cutting concerns (such as authentication, gateway functionality, etc.).
• The validated/processed request is forwarded to the main application.

Common use cases:

• API Gateway
• User Authentication
• Request rate limiting

Mode 2: Sidecar as a Companion Service

In this mode:

• External traffic is sent directly to the main application.
• The sidecar runs alongside the main application, providing auxiliary operations.
• The main application performs supporting functions by communicating with the sidecar.

Common use cases:

• Logging
• monitor
• Configuration Management

Real-world example: Sidecar vs. non-Sidecar

Non-Sidecar Mode

 public class PaymentService { public void processPayment(Payment payment) { // 处理支付逻辑validatePayment(payment); // 记录日志logger.info("Processing payment: " + payment.getId()); // 加密敏感数据encryptData(payment); // 记录监控指标recordMetrics(payment); // 执行支付处理executePayment(payment); } private void validatePayment(Payment payment) { /* ... */ } private void encryptData(Payment payment) { /* ... */ } private void recordMetrics(Payment payment) { /* ... */ } private void executePayment(Payment payment) { /* ... */ } }

Adopting the Sidecar Model

Main application:

 public class PaymentService { public void processPayment(Payment payment) { // 专注于核心支付逻辑validatePayment(payment); executePayment(payment); } private void validatePayment(Payment payment) { /* ... */ } private void executePayment(Payment payment) { /* ... */ } }

Sidecar components:

 public class PaymentSidecar { public void beforePaymentProcess(Payment payment) { // 处理跨领域关注点logTransaction(payment); encryptData(payment); recordMetrics(payment); } private void logTransaction(Payment payment) { /* ... */ } private void encryptData(Payment payment) { /* ... */ } private void recordMetrics(Payment payment) { /* ... */ } }

Best Practices for the Sidecar Pattern

Keep it simple:

• Use Sidecar mode only when you explicitly need it.
• Strictly define the responsibilities of the main application and the sidecar to avoid functional overload.

Handle failure gracefully:

• Use circuit breakers and fallback mechanisms to ensure that the core functions of the system can operate normally when the sidecar component fails.

Prioritize safety:

• Encrypted communication channels, strong authentication, and regular security audits.
• Ensure access controls and logging are in place to maintain system integrity.

Challenges and considerations

Performance impact:

• The Sidecar mode increases additional network communication and resource consumption.
• Cache and capacity planning is required to alleviate performance burden.

Increased complexity:

• More containers and configurations need to be managed, which brings additional operational burden.

Deployment Challenges:

• Version compatibility and update requirements for sidecars may make deployment more complex.

Test complexity:

• A more comprehensive testing strategy is needed to verify component interactions, simulate network failures, and test performance bottlenecks.

in conclusion

The sidecar pattern is a powerful architectural solution for managing cross-cutting concerns in distributed systems. Although it introduces some complexity, its advantages in isolation, maintainability, and flexibility generally outweigh the challenges.

Key points:

• Suitable for scenarios where cross-cutting concerns need to be isolated.
• Consider performance and resource costs.
• Follow best practices for communication and deployment.
• Effectively monitor and manage in production environments.