Let's Encrypt Auto-Renewal using the Webroot Plugin (Nginx)

le-renew-webroot

#!/bin/bash

web_service='nginx'
config_file="/usr/local/etc/le-renew-webroot.ini"

le_path='/opt/letsencrypt'
exp_limit=30;

if [ ! -f $config_file ]; then
        echo "[ERROR] config file does not exist: $config_file"
        exit 1;
fi

domain=`grep "^\s*domains" $config_file | sed "s/^\s*domains\s*=\s*//" | sed 's/(\s*)\|,.*$//'`
cert_file="/etc/letsencrypt/live/$domain/fullchain.pem"

if [ ! -f $cert_file ]; then
	echo "[ERROR] certificate file not found for domain $domain."
fi

exp=$(date -d "`openssl x509 -in $cert_file -text -noout|grep "Not After"|cut -c 25-`" +%s)
datenow=$(date -d "now" +%s)
days_exp=$(echo \( $exp - $datenow \) / 86400 |bc)

echo "Checking expiration date for $domain..."

if [ "$days_exp" -gt "$exp_limit" ] ; then
	echo "The certificate is up to date, no need for renewal ($days_exp days left)."
	exit 0;
else
	echo "The certificate for $domain is about to expire soon. Starting webroot renewal script..."
        $le_path/letsencrypt-auto certonly -a webroot --agree-tos --renew-by-default --config $config_file
	echo "Reloading $web_service"
	/usr/sbin/service $web_service reload
	echo "Renewal process finished for domain $domain"
	exit 0;
fi

le-renew-webroot.ini

# This is an example of the kind of things you can do in a configuration file.
# All flags used by the client can be configured here. Run Let's Encrypt with
# "--help" to learn more about the available options.

# Use a 4096 bit RSA key instead of 2048
rsa-key-size = 4096

# Always use the staging/testing server
# server = https://acme-staging.api.letsencrypt.org/directory

# Uncomment and update to register with the specified e-mail address
email = you@example.com

# Uncomment and update to generate certificates for the specified
# domains.
domains = example.com, www.example.com

# Uncomment to use a text interface instead of ncurses
# text = True

# Uncomment to use the standalone authenticator on port 443
# authenticator = standalone
# standalone-supported-challenges = tls-sni-01

# Uncomment to use the webroot authenticator. Replace webroot-path with the
# path to the public_html / webroot folder being served by your web server.
# authenticator = webroot
webroot-path = /usr/share/nginx/html

Recently I discovered that I don't need this script anymore...
I simply skip the --renew-by-default flag and certbot will renew the certificate only 30 days before it expires. To restart my service I use the --post-hook flag.