Bash script for custom Redis monitoring. The path in the mentioned cronjob is assuming the contents would be placed in a file called `monitor`, which resides in a folder `redis-monitoring` (within the HOME folder)

redis-monitoring

#!/bin/bash

#####################################################################################
# 																					#
# Cronjob command:																	#
# 																					#
# bash /home/DA_USER/redis-monitoring/monitor >/dev/null 2>&1						#
# 																					#
#####################################################################################



#################################
# Variables						#
#################################
# URL to check as part of the monitoring (must be the correct end-domain that normally results in 200 OK)
REDIS_MNTR_URL='https://domain.com'

# Email address to sent log-files to
REDIS_MNTR_EMAIL="[email protected]"

# Redis database number
REDIS_MNTR_DB='0'

# Redis key name
REDIS_MNTR_KEY='redis_monitoring_key'

# Number of times an error has to occur before emailing
REDIS_MNTR_NUM_CHECKS='5'

# Flush the Redis database (or not) when the number of REDIS_MNTR_NUM_CHECKS unsuccessful checks is reached
REDIS_MNTR_FLUSH_DB='true'

# Delete `object-cache.php` from `wp-content` when the number of REDIS_MNTR_NUM_CHECKS unsuccessful checks is reached
REDIS_MNTR_DEL_OBJCACHE='true'

# Base for the email subject, %s = domain from REDIS_MNTR_URL
REDIS_MNTR_MAIL_SUBJECT="CRITICAL: Redis issue — %s"

# Base for the email contents, %d = REDIS_MNTR_NUM_CHECKS, %s = REDIS_MNTR_URL
REDIS_MNTR_MAIL_CONTENTS="%d Redis errors on %s!\n\n Check the attached logfile."

# Path to Redis
REDIS_MNTR_PATH='/tmp/redis.sock'


#################################
# Files							#
#################################
REDIS_MNTR_FILE="${HOME}/redis-monitoring/redis-monitoring-file.txt"
REDIS_MNTR_LOG="${HOME}/redis-monitoring/redis-monitoring.log"



REDIS_MNTR_DATETIME_START=$(date)

# Get HTTP Status for REDIS_MNTR_URL
REDIS_MNTR_URL_STATUS=$(curl --write-out %{http_code} --silent --output /dev/null ${REDIS_MNTR_URL})


case ${REDIS_MNTR_URL_STATUS} in

	# HTTP STATUS equals 500, 503, or 507 (200 as well, just to be sure)
	200 | 500 | 503 | 507)
		
		# Write to log-file
		echo "[$(date +%d-%m-%Y\ %T)] ${REDIS_MNTR_URL_STATUS} — ${REDIS_MNTR_URL}" >> ${REDIS_MNTR_LOG}
		
		
		# Ping Redis
		REDIS_MNTR_PING=$(redis-cli -s ${REDIS_MNTR_PATH} -n ${REDIS_MNTR_DB} PING 2>&1)
		
		# Redis returned PONG
		if [ "${REDIS_MNTR_PING}" == "PONG" ] ; then
		
			# Set the Redis monitoring key in the database
			REDIS_MNTR_SETKEY=$(redis-cli -s /tmp/redis.sock -n ${REDIS_MNTR_DB} set ${REDIS_MNTR_KEY} "${REDIS_MNTR_DATETIME_START}" 2>&1)
			
			
			# Response from setting key was OK
			if [ "${REDIS_MNTR_SETKEY}" == "OK" ] ; then
			
				# Get the value of the key we've set
				REDIS_MNTR_GETKEY=$(redis-cli -s /tmp/redis.sock -n ${REDIS_MNTR_DB} get ${REDIS_MNTR_KEY} 2>&1)
				
				# When the set value and what was returned aren't the same
				if [ "${REDIS_MNTR_DATETIME_START}" != "${REDIS_MNTR_GETKEY}" ] ; then
				
					# Write to log-file
					echo "[$(date +%d-%m-%Y\ %T)] ERROR — ${REDIS_MNTR_GETKEY}" >> ${REDIS_MNTR_LOG}
					
					# Write to monitoring-file
					echo "[$(date +%d-%m-%Y\ %T)] ERROR" >> ${REDIS_MNTR_FILE}
				
				fi
				
			fi
			
			
			# Another Redis check, to be sure
			REDIS_MNTR_CHECK=$(redis-cli -s ${REDIS_MNTR_PATH} -n ${REDIS_MNTR_DB} INFO 2>&1)
			REDIS_MNTR_CHECK_FC=$(printf %.7s "${REDIS_MNTR_CHECK}")
			
			# First 7 characters are `(error)`
			if [ "${REDIS_MNTR_CHECK_FC}" == "(error)" ] ; then
				
				# Write to log-file
				echo "[$(date +%d-%m-%Y\ %T)] ERROR — ${REDIS_MNTR_CHECK}" >> ${REDIS_MNTR_LOG}
				
				# Write to monitoring-file
				echo "[$(date +%d-%m-%Y\ %T)] ERROR" >> ${REDIS_MNTR_FILE}
			
			# No Redis error
			else
			
				# HTTP Status 200 OK
				if [[ ${REDIS_MNTR_URL_STATUS} -eq 200 ]] ; then
			
					# Make sure REDIS_MNTR_NUM_CHECKS won't be reached unnecessarily
					# And the logfile can't keep growing 
					# So, remove both files
					rm -rf ${REDIS_MNTR_LOG}
					rm -rf ${REDIS_MNTR_FILE}
					
					# No need to keep going, so we're exiting
					exit 1
			
				fi
			
			fi
			
			
		# No PONG means no Redis
		else
		
			# Write to log-file
			echo "[$(date +%d-%m-%Y\ %T)] PING ERROR — ${REDIS_MNTR_PING}" >> ${REDIS_MNTR_LOG}
			
			# Write to monitoring-file
			echo "[$(date +%d-%m-%Y\ %T)] PING ERROR" >> ${REDIS_MNTR_FILE}
		
		fi
		
		
		# Write to log-file
		echo "——————————————————————————————————————————————————————————————————————————————" >> ${REDIS_MNTR_LOG}
		echo "" >> ${REDIS_MNTR_LOG}
		
		
		# If the Redis-monitoring file exists
		if [ -f "${REDIS_MNTR_FILE}" ]; then
		
			# Get number of lines in monitoring file (REDIS_MNTR_FILE)
			REDIS_MNTR_FILE_LC=$(wc -l < ${REDIS_MNTR_FILE})
			
			# The monitoring file contains an equal amount of lines as set with REDIS_MNTR_NUM_CHECKS
			if [ ${REDIS_MNTR_FILE_LC} -ge ${REDIS_MNTR_NUM_CHECKS} ] ; then
			
				# If REDIS_MNTR_FLUSH_DB is set to flush
				if [ "${REDIS_MNTR_FLUSH_DB}" == "true" ] ; then
				
					# Try to flush Redis DB
					REDIS_MNTR_FLUSHED=$(redis-cli -n ${REDIS_MNTR_DB} -s ${REDIS_MNTR_PATH} FLUSHDB 2>&1)
				
					# Check if Redis DB was flushed
					if [ "${REDIS_MNTR_FLUSHED}" == "OK" ] ; then
					
						echo "[$(date +%d-%m-%Y\ %T)] Redis DB ${REDIS_MNTR_DB} flushed" >> ${REDIS_MNTR_LOG}
					
					else
					
						echo "[$(date +%d-%m-%Y\ %T)] ERROR: Redis DB ${REDIS_MNTR_DB} | ${REDIS_MNTR_FLUSHED}" >> ${REDIS_MNTR_LOG}
						
						# If REDIS_MNTR_DEL_OBJCACHE is set to true
						if [ "${REDIS_MNTR_DEL_OBJCACHE}" == "true" ] ; then
						
							# Delete `object-cache.php`
							rm -rf "${HOME}/domains/${REDIS_MNTR_DOMAIN}/public_html/wp-content/object-cache.php"
							
							# Log it
							echo "[$(date +%d-%m-%Y\ %T)] object-cache.php deleted" >> ${REDIS_MNTR_LOG}
						
						fi
					
					fi
				
				# REDIS_MNTR_FLUSH_DB is false, but REDIS_MNTR_DEL_OBJCACHE is true
				elif [ "${REDIS_MNTR_DEL_OBJCACHE}" == "true" ] ; then
					
					# Delete `object-cache.php`
					rm -rf "${HOME}/domains/${REDIS_MNTR_DOMAIN}/public_html/wp-content/object-cache.php"
					
					# Log it
					echo "[$(date +%d-%m-%Y\ %T)] object-cache.php deleted" >> ${REDIS_MNTR_LOG}
					
				fi
				
				
				# Get the domain from the monitor URL
				REDIS_MNTR_DOMAIN=$(echo "${REDIS_MNTR_URL}" | awk -F/ '{print $3}')
				
				# Set the email subject
				REDIS_MNTR_SUBJECT=$(printf "${REDIS_MNTR_MAIL_SUBJECT}" "${REDIS_MNTR_DOMAIN}")
				
				# Set the email contents
				REDIS_MNTR_MAIL_CONTENT=$(printf "${REDIS_MNTR_MAIL_CONTENTS}" "${REDIS_MNTR_NUM_CHECKS}" "${REDIS_MNTR_URL}")
				
				# Email the logfile
				echo "${REDIS_MNTR_MAIL_CONTENT}" | mail -s "${REDIS_MNTR_SUBJECT}" -a ${REDIS_MNTR_LOG} "${REDIS_MNTR_EMAIL}"
				
				
				# Remove both files to start over
				rm -rf ${REDIS_MNTR_LOG}
				rm -rf ${REDIS_MNTR_FILE}
				
			fi
		
		fi
	
	;;


	# Default / all other HTTP STATUS codes
	*)
		# Nothing else needed, so we're exiting
		exit 1
	;;
esac