High-level design

Core Components

API Gateway
- Serves as the entry point for all client requests.
- Routes requests to appropriate services, such as the Tile Retrieval Service, Metadata Service, or Authentication Service.
- Performs rate limiting, logging, and basic authentication.
Tile Retrieval Service
- Handles requests for retrieving image tiles based on zoom level and tile coordinates.
- Performs caching using a distributed in-memory cache (e.g., Redis).
- Interacts with the Image Storage Service to retrieve image files if not found in the cache.
Image Processing Service
- Processes raw images to generate tiles at different zoom levels.
- Uses geospatial libraries (e.g., GDAL) to slice, compress, and optimize image files for efficient storage and retrieval.
- Stores processed tiles in the Image Storage Service.
Image Storage Service
- Manages the storage of image tiles using a distributed storage system (e.g., Amazon S3).
- Handles storage of image metadata in a relational database (e.g., PostgreSQL with PostGIS).
- Provides efficient read and write access to image files for the Tile Retrieval Service.
Authentication Service
- Manages user authentication and issues JWT tokens.
- Interacts with the Users table in the database to validate credentials and permissions.
Metadata Service
- Provides metadata about stored images, such as region bounds, available zoom levels, and resolution.
- Interacts with the Regions and Images tables in the database.
Distributed Cache
- Caches frequently requested tiles to minimize database and storage system load.
- Supports cache invalidation mechanisms to keep data consistent.
Content Delivery Network (CDN)
- Caches image tiles at edge locations to minimize latency for global users.
- Works in conjunction with the Tile Retrieval Service to deliver images quickly.

graph TD
    A[API Gateway] --> B[Tile Retrieval Service]
    A --> C[Metadata Service]
    A --> D[Authentication Service]
    
    B --> E[Distributed Cache]
    E --> F[Image Storage Service]
    F --> G[Object Storage]

    C --> F
    D --> H[User Database]
    
    F --> I[Processing Service]
    I --> G
    
    B --> J[Content Delivery Network]
    J --> K[End Users]

Design Flow

User Request Handling: All requests from clients are first routed through the API Gateway. The gateway handles authentication and then forwards the request to the appropriate service.
Tile Retrieval:
- The Tile Retrieval Service first checks the Distributed Cache to see if the requested tile is available.
- If the tile is not in the cache, the service fetches it from the Image Storage Service.
- If the tile does not exist in storage, the request is forwarded to the Image Processing Service to generate it.
- The Content Delivery Network (CDN) caches the tile at edge locations after it is retrieved, reducing latency for subsequent requests.
Metadata Retrieval: The Metadata Service retrieves information from the relational database (e.g., Regions and Images tables) to provide metadata for querying or filtering tiles.
Image Processing: New images are uploaded to the Object Storage by administrators. The Image Processing Service slices the images into tiles at multiple zoom levels and stores the processed tiles in the Image Storage Service.
User Authentication: User credentials are verified by the Authentication Service, which issues JWT tokens that the API Gateway uses for validating subsequent requests.

Submissions

Displaying Solutions with Scores Ranging from 1 to 10