host-port-ingress-proxy

1. Docker Container Setup:

   • The Docker container is based on the official NGINX Alpine image.
   • Several environment variables are defined in the Dockerfile to configure the NGINX reverse proxy. These include BACKEND_HOST, BACKEND_TCP_PORT, BACKEND_UDP_PORT, and ALLOWED_IPS.
   • The Dockerfile also installs curl for health checking purposes and includes a custom entrypoint script.

2. NGINX Configuration:

   • A template for the NGINX configuration (nginx.conf.template) is used. This template is processed by the entrypoint script (entrypoint.sh) to replace placeholders with the actual environment variable values.
   • The NGINX configuration sets up NGINX as a reverse proxy to forward TCP and UDP traffic to the configured backend host and ports. It also includes IP-based access control.
   • Additionally, NGINX listens on a separate HTTP port (8080) with a specific location (/healthz) that always returns a 200 OK response. This endpoint is used for health checks.

3. Health Checking:

   • The Dockerfile defines a HEALTHCHECK instruction that uses curl to periodically check the health of the NGINX server by accessing the /healthz endpoint.
   • If the health check fails (does not return 200 OK), Docker marks the container as unhealthy.

4. Running the Container:

   • When the container is run, the environment variables can be set to define the backend host, ports, and allowed IPs.
   • Docker's health check mechanism monitors the container's health status by checking the /healthz endpoint.

Mermaid Diagram

Here's a Mermaid diagram that visualizes the flow:

graph LR
    subgraph Docker Container
    NGINX[NGINX Reverse Proxy]
    ENTRYPOINT[Entrypoint Script]
    CONFIG[nginx.conf.template]
    HEALTHCHECK[Health Check]

    ENTRYPOINT -->|Processes| CONFIG
    CONFIG -->|Configures| NGINX
    NGINX -->|TCP/UDP Proxy| BACKEND[Backend Service]
    NGINX -->|HTTP Health Check| HEALTHCHECK
    HEALTHCHECK -->|curl /healthz| NGINX
    end

    USER[User] -->|TCP/UDP Request| NGINX
    NGINX -->|Responds| USER
    DOCKER[Docker Daemon] -->|Periodic Check| HEALTHCHECK

    style NGINX fill:#f96,stroke:#333,stroke-width:2px
    style BACKEND fill:#ff9,stroke:#333,stroke-width:2px
    style USER fill:#9f6,stroke:#333,stroke-width:2px
    style HEALTHCHECK fill:#6f9,stroke:#333,stroke-width:2px
    style DOCKER fill:#f69,stroke:#333,stroke-width:2px

This diagram represents the flow of requests through the NGINX reverse proxy and how the health check mechanism works within the Docker container. The NGINX Reverse Proxy handles both TCP/UDP requests and health check requests, forwarding the former to the Backend Service and responding directly to the latter. The Docker Daemon periodically triggers the health check to ensure the NGINX server is functioning correctly.