Just a simple Mysql Replication Health Check script I wrote. You can put this in a cron.

MySQL Replication Check

#!/bin/bash

### VARIABLES ### \
EMAIL=""
SERVER=$(hostname)
MYSQL_CHECK=$(mysql -e "SHOW VARIABLES LIKE '%version%';" || echo 1)
LAST_ERRNO=$(/usr/bin/mysql -e "SHOW SLAVE STATUS\G" | grep "Last_Errno" | awk '{ print $2 }')
SECONDS_BEHIND_MASTER=$(/usr/bin/mysql -e "SHOW SLAVE STATUS\G"| grep "Seconds_Behind_Master" | awk '{ print $2 }')
IO_IS_RUNNING=$(/usr/bin/mysql -e "SHOW SLAVE STATUS\G" | grep "Slave_IO_Running" | awk '{ print $2 }')
SQL_IS_RUNNING=$(/usr/bin/mysql -e "SHOW SLAVE STATUS\G" | grep "Slave_SQL_Running" | awk '{ print $2 }')
ERRORS=()

### Run Some Checks ###

## Check if I can connect to Mysql ##
if [ "$MYSQL_CHECK" == 1 ]
then
    ERRORS=("${ERRORS[@]}" "Can't connect to MySQL (Check Pass)")
fi

## Check For Last Error ##
if [ "$LAST_ERRNO" != 0 ]
then
    ERRORS=("${ERRORS[@]}" "Error when processing relay log (Last_Errno)")
fi

## Check if IO thread is running ##
if [ "$IO_IS_RUNNING" != "Yes" ]
then
    ERRORS=("${ERRORS[@]}" "I/O thread for reading the master's binary log is not running (Slave_IO_Running)")
fi

## Check for SQL thread ##
if [ "$SQL_IS_RUNNING" != "Yes" ]
then
    ERRORS=("${ERRORS[@]}" "SQL thread for executing events in the relay log is not running (Slave_SQL_Running)")
fi

## Check how slow the slave is ##
if [ "$SECONDS_BEHIND_MASTER" == "NULL" ]
then
    ERRORS=("${ERRORS[@]}" "The Slave is reporting 'NULL' (Seconds_Behind_Master)")
elif [ "$SECONDS_BEHIND_MASTER" > 60 ]
then
    ERRORS=("${ERRORS[@]}" "The Slave is at least 60 seconds behind the master (Seconds_Behind_Master)")
fi

### Send and Email if there is an error ###
if [ "${#ERRORS[@]}" -gt 0 ]
then
    MESSAGE="An error has been detected on ${SERVER} involving the mysql replciation. Below is a list of the reported errors:\n\n
    $(for i in $(seq 1 ${#ERRORS[@]}) ; do echo "\t${ERRORS[$i]}\n" ; done)
    Please correct this ASAP
    "
    echo -e $MESSAGE | mail -s "Mysql Replication for $SERVER is reporting Error" ${EMAIL}
fi

Checkout for the login-path option in MySQL client so you can sleep at night knowing your MySQL root user is not in pure plain-text, as suggested previously here.

1. Generate a login-path using mysql_config_editor as explained here.
2. Add the --login-path option: MYSQL_CHECK=$(mysql --login-path=login_path_generated -e "SHOW VARIABLES LIKE '%version%';" || echo 1) in other statements as well.

The file encryption can be cracked, so ensure no one beside root have access to it.

Nice script.

Forked here if anyone wants to see the revision

Added some extra checks.

Used --login-path=mysql_login instead of using a mysql -u -p via the mysql_config_editor

Added SSMTP sending of email instead of something like postfix.

Added AWS S3 backup granted the check goes through ok.

Changed it to utilise the $STATUS_LINE variable instead of calling multiple times to SHOW SLAVE STATUS

Few other changes as per the comments above.