Comprehensive Guide to Setting Up Cron Jobs in Ubuntu and Frappe Including SSL Renewal on a DigitalOcean Droplet

Understanding Cron Jobs in Linux

Cron jobs are scheduled tasks executed automatically at specified times and dates. In Linux, cron schedules are defined in the format:

* * * * * command to execute

Each asterisk represents: - Minute (0-59) - Hour (0-23) - Day of Month (1-31) - Month (1-12) - Day of Week (0-6) (Sunday=0)

Examples:

10 14 * * 1: Executes at 2:10 PM every Monday.
0 3 * * 0: Executes at 3:00 AM every Sunday.

Setting Up Cron Jobs on Ubuntu

Step 1: Accessing Cron Jobs

Open the crontab editor:

sudo crontab -e

Choose your preferred text editor (nano, vim).

Step 2: Adding a Cron Job

To schedule a script or command, add a new line in the editor:

10 14 * * 1 /path/to/script.sh >> /path/to/logfile.log 2>&1

This runs the script every Monday at 2:10 PM, logging output and errors to logfile.log.

Step 3: Saving and Exiting

Nano: Press Ctrl+O (save), then Ctrl+X (exit).
Vim: Press Esc, type :wq, and press Enter.

Setting Up Cron Jobs in Frappe

Frappe allows scheduling tasks using the bench environment.

Step 1: Create Scheduled Tasks

In Frappe apps, scheduled tasks are defined in the hooks.py file:

scheduler_events = {
    "daily": [
        "your_app.tasks.daily_task"
    ],
    "weekly": [
        "your_app.tasks.weekly_task"
    ]
}

Step 2: Implement Tasks in Python

In your app (tasks.py):

import frappe

def daily_task():
    frappe.logger().info("Running daily task")


def weekly_task():
    frappe.logger().info("Running weekly task")

Frappe automatically manages execution according to your defined schedule.

Renewing SSL Certificates Automatically in Frappe (DigitalOcean Droplet)

Step 1: Setting Up Cron Job for SSL Renewal

Open the root crontab:

sudo crontab -e

Add the following cron job to renew SSL certificates weekly (every Sunday at 3 AM):

0 3 * * 0 cd /home/frappe/frappe-bench && /usr/local/bin/bench renew-lets-encrypt >> /home/frappe/frappe-bench/logs/letsencrypt-renew.log 2>&1

Explanation:

cd /home/frappe/frappe-bench: Navigates to the Frappe bench directory.
/usr/local/bin/bench renew-lets-encrypt: Runs SSL renewal.
Logs output/errors to letsencrypt-renew.log for troubleshooting.

Step 2: Verifying Bench Command Path

Ensure the bench command path is correct:

which bench

Usually returns /usr/local/bin/bench. Adjust if needed.

Step 3: Testing Manually

Test the SSL renewal manually:

cd /home/frappe/frappe-bench
sudo bench renew-lets-encrypt

Ensure successful execution.

Step 4: Checking SSL Certificate Validity

Use the following command to verify the validity period of your SSL certificates:

sudo openssl x509 -enddate -noout -in /etc/letsencrypt/live/yourdomain.com/fullchain.pem

Replace yourdomain.com with your actual domain.

🔁 Alternative to `certbot` for Checking SSL Expiry

If certbot is unavailable or throws an error, you can check the SSL certificate expiry date using openssl:

echo | openssl s_client -servername yourdomain.com -connect yourdomain.com:443 2>/dev/null | openssl x509 -noout -enddate

Cron Job Troubleshooting

Check Logs: Regularly check logs in /home/frappe/frappe-bench/logs/.
Permission Issues: Always use absolute paths and correct user permissions.

By following these guidelines, you ensure automated, reliable task execution and SSL certificate management for your Ubuntu-based Frappe application hosted on DigitalOcean.

Comprehensive Guide to Setting Up Cron Jobs in Ubuntu and Frappe Including SSL Renewal on a DigitalOcean Droplet