Monitor SSL certificate expiry dates with Google Sheets & Slack alerts

> ⚠️ Notice:
> Community nodes like @custom-js/n8n-nodes-pdf-toolkit can only be installed on self-hosted instances of n8n.

This n8n workflow illustrates how to monitor and track SSL certificate expiration dates for any domain using the SSL Checker node from customJS. It automatically updates a Google Sheet with the number of days left until expiry and sends a Slack notification when certificates are about to expire.

What this workflow does

• Input a list of domains from Google Sheets.
• Check each domain’s SSL certificate details, including expiration date and days left.
• Update the Google Sheet with the latest SSL expiry information.
• Notify via Slack if any certificate is expiring soon (e.g., less than 8 days).

Requirements

• Self-hosted n8n instance.
• CustomJS API key for SSL checking.
• Google Sheets API credentials for reading/updating domain data.
• Slack API credentials (optional, for notifications).

Workflow Steps

1. Schedule Trigger

   • ⏰ Starts the workflow automatically (weekly by default, configurable).

2. Google Sheets (Read Rows)

   • 📄 Retrieves the list of domains from your Google Sheet.

3. SSL Checker (CustomJS node)

   • 🔐 Fetches SSL certificate details for each domain.
   • Returns JSON output with fields such as expires and daysLeft.

4. Google Sheets (Update Rows)

   • 📝 Updates the sheet with the current number of days left until certificate expiry.

5. Check Days Left Threshold (formerly "If" node)

   • ⚠️ Evaluates whether the certificate expires within the threshold (e.g., < 8 days).

6. Slack Node

   • 💬 Sends a notification message if a certificate is close to expiration.

   Example Slack alert message:

   ⏰ Reminder: SSL certificate of www.example.com 
   will expire in 7 days.
   

SSL Checker node JSON output

{
  "output": {
    "domain": "example.com",
    "valid": true,
    "expires": "2025-12-31T23:59:59.000Z",
    "issuer": "Let's Encrypt",
    "daysLeft": 5
  }
}