CORS implemented in a static manner: unable to configure on another machine

specs/008-deploy-to-hosting/research.md

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+# Research: Deployment Configuration
+
+**Date**: 2025-10-15
+
+This document outlines the technical decisions made to enable deploying the application to a custom host.
+
+## 1. Backend CORS Configuration
+
+- **Decision**: Use the `cors` npm package in the Express.js backend to manage Cross-Origin Resource Sharing.
+- **Rationale**: It is the industry-standard, robust, and highly configurable middleware for enabling CORS in Node.js. It provides a simple way to whitelist origins, which directly addresses FR1.
+- **Alternatives Considered**: Manually setting CORS headers. This is error-prone and less maintainable than using a dedicated, well-tested library.
+
+## 2. Environment-based Configuration
+
+- **Decision**: All deployment-specific values (CORS origins, API URLs) will be managed through environment variables.
+- **Rationale**: This decouples configuration from the codebase, adhering to Twelve-Factor App principles. It allows developers to easily switch between `localhost` and production environments without changing code.
+- **Alternatives Considered**: Hardcoding values (violates principles), using configuration files (less flexible than environment variables in containerized environments).
+
+## 3. Frontend to Backend Communication
+
+- **Decision**: The frontend will use a `REACT_APP_API_URL` environment variable to determine the backend's address.
+- **Rationale**: This is the standard convention for Create React App applications. It ensures the frontend can be pointed to any backend during development or after deployment.
+- **Alternatives Considered**: None, as this is the idiomatic approach for this frontend stack.
+
+## 4. Docker Configuration
+
+- **Decision**: The `docker-compose.yaml` file will be updated to pass host-level environment variables into the respective `frontend` and `backend` service containers.
+- **Rationale**: This is the standard and most effective method for injecting runtime configuration into Docker Compose services, allowing for flexible deployment.
+- **Alternatives Considered**: Building separate images for each environment (inefficient), managing configuration inside the container (violates immutability principles).