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The AB Test Assignment API Route is a critical component of the Sophra System’s experimentation framework, providing a robust and scalable solution for variant assignment in A/B testing scenarios. This Next.js API route, implemented using TypeScript, serves as the entry point for client applications seeking to participate in ongoing experiments. It leverages Sophra’s microservices architecture to interact with the AB Testing service, ensuring consistent and statistically sound variant assignments across the platform. At its core, this component embodies the principles of separation of concerns and modular design. It acts as a thin API layer, delegating the complex logic of variant assignment to specialized services while focusing on request validation, error handling, and response formatting. This architectural decision enhances maintainability and allows for independent scaling of the API layer and the underlying AB testing infrastructure. The route implements a comprehensive error handling strategy, capturing and categorizing errors at multiple levels - from service initialization failures to invalid request parameters. This approach not only improves the robustness of the system but also provides valuable debugging information for developers and detailed feedback for API consumers. The integration with Sophra’s logging and metrics services ensures that every assignment request, successful or not, contributes to the system’s observability and performance tracking. Performance optimization is a key consideration in the design of this component. By leveraging Next.js’s API routes, it benefits from serverless deployment options, allowing for automatic scaling based on incoming traffic. The use of a schema validation library (Zod) for request parsing strikes a balance between runtime performance and type safety. Moreover, the component includes latency tracking, providing insights into the efficiency of the variant assignment process. One of the unique features of this API route is its flexibility in test identification. It supports both direct test ID references and lookup by test name, accommodating different client implementation preferences without compromising on performance. This dual approach enhances the developer experience while maintaining the system’s ability to handle high-volume assignment requests efficiently.

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Exported Components

export const runtime = "nodejs";

export async function POST(req: Request): Promise<NextResponse>
The POST function is the main export of this module, conforming to the Next.js API route signature. It handles incoming HTTP POST requests and returns a NextResponse object.

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Parameters

  • req: Request - The incoming HTTP request object

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Return Type

  • Promise<NextResponse> - A promise that resolves to a NextResponse object containing the API response

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Implementation Examples

// Example usage in a client application
const response = await fetch('/api/cortex/ab-test/assign', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    sessionId: 'user123',
    testId: 'experiment-456',
  }),
});

const result = await response.json();
if (result.success) {
  console.log(`Assigned variant: ${result.data.variantId}`);
} else {
  console.error(`Assignment failed: ${result.error}`);
}

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Sophra Integration Details

This component integrates tightly with several Sophra services:
  1. AB Testing Service: Used for variant assignment and test lookup.
  2. Metrics Service: Records latency and success metrics for each assignment.
  3. Logger: Provides detailed logging throughout the request lifecycle.

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Error Handling

The component implements a multi-layered error handling strategy:
  1. Service Initialization Errors: Captured and logged with available service details.
  2. Request Validation Errors: Parsed using Zod and returned with specific field errors.
  3. Business Logic Errors: Such as test not found or no eligible variants.
  4. Unexpected Errors: Caught in a global try-catch block, logged, and returned as 500 errors.
All errors are logged with contextual information, including raw request bodies and stack traces where applicable, to facilitate debugging and monitoring.

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Performance Considerations

While this component doesn’t implement direct caching, it’s designed to work with Sophra’s distributed caching layer. The AB Testing service can potentially cache variant assignments for repeated sessionId-testId combinations, reducing database load.
Each request’s latency is measured and recorded using the Metrics service, allowing for performance monitoring and optimization over time.
The use of Zod for request validation provides a balance between runtime performance and type safety, ensuring fast and accurate request processing.

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Security Implementation

Authentication and Authorization

This route assumes that authentication has been handled by upstream middleware. It’s crucial to ensure that this endpoint is properly protected in the overall API gateway configuration.

Input Validation

Strict input validation using Zod schema ensures that only well-formed requests are processed, mitigating potential injection attacks.

Error Information Leakage

Error responses are carefully constructed to provide useful information to clients without exposing sensitive system details.

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Configuration

The component relies on the following environment variables and configuration options: 
POSTGRESQL_URL="your-database-url"
ELASTICSEARCH_URL="your-elasticsearch-url"
ELASTICSEARCH_API_KEY="your-elasticsearch-api-key"
SOPHRA_REDIS_URL="your-redis-url"
These configurations are typically managed through the Sophra service manager and don’t need to be directly accessed within this component.
Ensure that all required services are properly initialized and configured in the Sophra service manager for this component to function correctly.
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