Monitoring Mainsail and Klipper 3D Printers with Vigilmon

Mainsail turns a Raspberry Pi into a professional 3D printer control center — real-time print progress, webcam streaming, G-code management, and remote access from any browser. But when Moonraker (the Python API bridge) crashes at hour 14 of a 20-hour print, you won't know until you check the webcam and see a cold, stalled extruder. Vigilmon watches your entire printing stack — Mainsail UI, Moonraker API, printer state, and webcam — and alerts you the moment something breaks.

What You'll Set Up

HTTP uptime monitor for the Mainsail web UI (nginx, port 80)
Moonraker API health check (port 7125)
Printer state endpoint response time monitoring (/printer/info)
Webcam stream availability check (mjpg-streamer/camera-streamer, port 8080)
TCP monitor for Moonraker socket connectivity
Alert channel configuration for print-failure notifications

Prerequisites

Mainsail installed and running (via MainsailOS, KIAUH, or manual setup)
Moonraker running on port 7125
A free Vigilmon account

Step 1: Monitor the Mainsail Web UI

Mainsail is served by nginx as a static Vue.js app. If nginx crashes or the Pi loses power, the web UI goes dark.

Log in to vigilmon.online and click Add Monitor.
Set Type to HTTP / HTTPS.
Enter your Mainsail URL: http://mainsail.local or http://YOUR_PI_IP.
Set Check interval to 2 minutes.
Set Expected HTTP status to 200.
Click Save.

If you've set up a domain with SSL (e.g. via Cloudflare Tunnel), use the HTTPS URL and enable Monitor SSL certificate with a 21-day alert threshold.

Step 2: Monitor the Moonraker API

Moonraker is the Python server that bridges Mainsail to Klipper. The web UI can appear available (nginx is up) while Moonraker is down — leaving you unable to start prints or read sensor data.

Add a dedicated Moonraker API health monitor:

Click Add Monitor → HTTP / HTTPS.
URL: http://YOUR_PI_IP:7125/server/info.
Set Check interval to 1 minute.
Set Expected HTTP status to 200.
Set Expected response body contains to moonraker.
Click Save.

The /server/info endpoint returns JSON including the Moonraker version and component status. A 200 with a valid JSON body confirms the API server is running.

# Verify manually
curl -s http://YOUR_PI_IP:7125/server/info | python3 -m json.tool

Step 3: Monitor Printer State via `/printer/info`

Even with Moonraker up, Klipper (the MCU firmware daemon) can disconnect from the printer board — a firmware exception, a loose USB cable, or a failed MCU update. The /printer/info endpoint exposes Klipper's connection state.

Click Add Monitor → HTTP / HTTPS.
URL: http://YOUR_PI_IP:7125/printer/info.
Check interval: 2 minutes.
Expected HTTP status: 200.
Expected response body contains: ready (Klipper reports state: "ready" when connected to the MCU).
Click Save.

A response containing "error" or "shutdown" in the state field means Klipper has crashed or the MCU is disconnected. Vigilmon will alert as soon as the expected string check fails.

Step 4: Monitor the Webcam Stream

Webcam streaming (mjpg-streamer or camera-streamer) runs on port 8080 independently of Moonraker. It can crash without affecting the print itself, but it leaves you flying blind on long jobs.

Click Add Monitor → HTTP / HTTPS.
URL: http://YOUR_PI_IP:8080/?action=stream (mjpg-streamer) or http://YOUR_PI_IP:8080/stream (camera-streamer).
Check interval: 5 minutes (streaming endpoints are heavier to probe).
Expected HTTP status: 200.
Click Save.

Alternatively, use the snapshot endpoint for a lighter check:

http://YOUR_PI_IP:8080/?action=snapshot

This fetches a single JPEG frame instead of initiating a stream connection, which is faster and more reliable for health checks.

Step 5: TCP Monitor for Moonraker Port

Add a TCP-level monitor to catch cases where Moonraker's HTTP server starts but the port becomes unresponsive (deadlock, socket exhaustion):

Click Add Monitor → TCP Port.
Host: YOUR_PI_IP.
Port: 7125.
Check interval: 1 minute.
Click Save.

Step 6: Heartbeat Monitor for Print Job Completion

For very long prints, you can send Vigilmon a heartbeat ping from a Moonraker macro or a small shell script that runs on the Pi to confirm the print is still progressing:

Click Add Monitor → Cron Heartbeat.
Set Expected interval to 30 minutes.
Copy the heartbeat URL.

Add a shell script on the Pi that checks print progress and pings Vigilmon:

#!/bin/bash
# /home/pi/check_print.sh
STATE=$(curl -s http://localhost:7125/printer/objects/query?print_stats \
  | python3 -c "import sys,json; d=json.load(sys.stdin); print(d['result']['status']['print_stats']['state'])")

if [ "$STATE" = "printing" ] || [ "$STATE" = "complete" ]; then
    curl -s https://vigilmon.online/heartbeat/YOUR_HEARTBEAT_ID
fi

Schedule it in crontab:

*/30 * * * * /home/pi/check_print.sh

If the Pi crashes or the print stalls without completing, the heartbeat stops and Vigilmon alerts.

Step 7: Configure Alert Channels

Long prints fail at inconvenient hours. Route alerts where you'll actually see them:

Go to Alert Channels in Vigilmon.
Add a Slack or Discord webhook for your home/lab notification channel.
Add an email alert as a backup.
On each Moonraker/printer monitor, set Consecutive failures before alert to 2 — this avoids false alarms from momentary API timeouts during high-load G-code processing.

For the webcam monitor, set the threshold to 3 — stream endpoints can be slow to respond during peak CPU usage (especially when running on a Pi 3).

Summary

| Monitor | Target | What It Catches | |---|---|---| | Mainsail UI | http://PI_IP:80 | nginx crash, Pi power loss | | Moonraker API | http://PI_IP:7125/server/info | Python API server down | | Printer state | http://PI_IP:7125/printer/info | Klipper MCU disconnect, firmware crash | | Webcam stream | http://PI_IP:8080/snapshot | Camera service crash | | TCP port | PI_IP:7125 | Moonraker socket unresponsive | | Cron heartbeat | Heartbeat URL | Pi crash during active print |

Mainsail gives you a beautiful interface for your Klipper printer — Vigilmon makes sure that interface and everything behind it stays up through 40-hour overnight prints.