palworldlol / check-port-api

A really simple API that responds UP or DOWN if a certain address+port combination is listening

check-port-api

This is a simpler health checker that acts as a proxy to check ports not exposed.

The API responds with either UP or DOWN if a TCP Connection is made to the target.

For example, I'm using this with a Palworld server like below. The goal being never to expose access to RCON to the internet.

sequenceDiagram
    participant Status Dashboard

    Note over Status Dashboard: (e.g. Uptime Kuma)
    
    box Server
    participant check-api-port
    participant RCON for Palworld
    end

    Status Dashboard ->> check-api-port: HTTP Request (no params)
    Note over Status Dashboard, check-api-port: Internet

    check-api-port ->> RCON for Palworld: TCP Connect
    Note over check-api-port, RCON for Palworld: No auth required

    RCON for Palworld ->> check-api-port: Connection Success
    check-api-port ->> Status Dashboard: "UP"

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Help

Host a really simple API that responds UP or DOWN if it finds a specific address+port is listenin.
This is useful to act as a proxy to check if a certain port is open on a system but its not actually exposed.

Usage:
  check-port-api [flags]

Flags:
      --check-host string    The hostname to check
      --check-port string    The port to check
  -h, --help                 help for check-port-api
      --listen-host string   The hostname to listen on (default "0.0.0.0")
      --listen-port string   The port to listen on (default "8181")
      --timeout duration     Timeout to check target (default 5s)

Docker

There is a docker container available: docker.io/bostrt/check-api-port:latest. Here is a very simple docker compose file for reference:

• Note the exposed port 8181 on check-port-api container.
• Note the usage of the docker compose service name palworld as host to check
• Note the RCON port 25575 is used but also is not exposed outside of the container network
• Lastly, note that the check-port-api container requires no knowledge of RCON credentials since only a TCP connect is performed

services:
  check-port-api:
    image: docker.io/bostrt/check-port-api:dev
    pull_policy: always
    restart: unless-stopped
    container_name: check-port-api
    ports:
      - 8181:8181/tcp
    depends_on:
      - palworld
    command:
      - --check-host=palworld
      - --check-port=25575
  palworld:
      image: thijsvanloef/palworld-server-docker:latest
      pull_policy: always
      restart: unless-stopped
      container_name: palworld-server
      ports:
        - 8211:8211/udp
        - 27015:27015/udp
      environment:
         - PUID=1000
         - PGID=1000
         - PORT=8211
         - PLAYERS=8
         - MULTITHREADING=true
         - RCON_ENABLED=true
         - RCON_PORT=25575
      volumes:
         - ./palworld:/palworld/:z

check-port-api's Issues

Log when hostname is not resolvable

Need to log an error when the --check-host value is not resolvable

Connection state cache

Need to use a really short-lived cache of the connection state to respond to health checks instead of querying every single time to reduce impact of spammmm