Simple CDN

simple_cdn is a lightweight Content Delivery Network (CDN) server written in Go. It provides caching, request proxying, and diagnostic features. This application is designed to handle HTTP requests, cache responses based on configurable rules, and serve cached content to reduce the load on the upstream servers.

Features

• Caching: Supports response caching with configurable rules for persistence and retrieval.
• Proxying: Forwards requests to an upstream server when caching is not applicable.
• Diagnostics: Includes a diagnostic server for health checks, metrics, and profiling.
• Logging and Metrics: Integrated logging and Prometheus metrics for observability.

Installation

To build the simple_cdn server, you need to have Go installed. Clone the repository and run the following command:

go build -o simple_cdn main.go

But actually, you can use docker image paragor/simple_cdn that have both arm64 and amd64 architectures.

Usage

Run the server with the following command:

LOG_LEVEL=info simple_cdn -config /path/to/config.yaml

Command-Line Options

• -config: Path to the YAML configuration file (required).
• -check-config: Validates the configuration file and exits without starting the server.

Configuration

See examples in ./examples/*.yaml

Configuration Parameters

• listen_addr: Address for the main server to listen on.
• diagnostic_addr: Address for the diagnostic server to listen on.
• can_persist_cache: Conditions under which responses can be cached.
• can_load_cache: Conditions under which cached responses can be served.
• can_force_emit_debug_logging: Conditions under which debug logging is forced.
• cache: Cache backend configuration (e.g., Redis).
• cache_key_config: Configuration for cache key generation based on cookies, headers, and query parameters.
• upstream: Configuration for the upstream server to which uncached requests are forwarded.
• ordered_cache_control_fallback: Config for override Cache-Control header if it is empty.

Diagnostic Server

The diagnostic server provides the following endpoints:

• /readyz: Readiness probe endpoint.
• /healthz: Health check endpoint.
• /invalidate: Endpoint to invalidate cached content based on a pattern. (/invalidate?pattern=/static/* - not regexp)
• /metrics: Prometheus metrics endpoint.
• /debug/pprof/: pprof profiling endpoints for performance diagnostics.

Logging

simple_cdn uses structured logging via zap for different log levels. The log level can be configured through the LOG_LEVEL environment variable (info, debug, error, warn).

Metrics

simple_cdn integrates with Prometheus for metrics collection. Metrics are exposed at the /metrics endpoint of the diagnostic server.