How do I schedule the Let's Encrypt certbot to automatically renew my certificate in cron?

I've seen conflicting recommendations. From the eff.org docs:

if you're setting up a cron or systemd job, we recommend running it twice per day... Please select a random minute within the hour for your renewal tasks.

I've also seen recommendations for weekly jobs.

I'm not a cron expert, so I'd prefer an answer with detailed steps for setting up the cron job.

Solution

I recently (April 2018) installed and ran certbot (version 0.22.2) on an Ubuntu 16.04 server, and a renewal cron job was created automatically in /etc/cron.d/certbot.

Here's the cron job that was created:

# /etc/cron.d/certbot: crontab entries for the certbot package
#
# Upstream recommends attempting renewal twice a day
#
# Eventually, this will be an opportunity to validate certificates
# haven't been revoked, etc.  Renewal will only occur if expiration
# is within 30 days.
SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

0 */12 * * * root test -x /usr/bin/certbot -a \! -d /run/systemd/system && perl -e 'sleep int(rand(3600))' && certbot -q renew

Please check this before putting a new Cron job.

Update (From @Hamish Downer's comment):

It's worth being aware that the above cron job won't run certbot renew if /run/systemd/system is present - this is because instead a systemd timer is running certbot - read more about certbot and systemd timers here.