Invoking Shell script with Upstart "start on socket"

mysqlchk

# /etc/xinetd.d/mysqlchk
# description: mysqlchk
service mysqlchk
{
        flags           = REUSE
        socket_type     = stream
        port            = 33066
        wait            = no
        user            = nobody
        server          = /opt/tools/mysqlchk.sh
        log_on_failure  += USERID
        disable         = no
#        only_from       = 0.0.0.0/0
# recommended to put the IPs that need
# to connect exclusively (security purposes)
        per_source      = UNLIMITED
# Recently added (May 20, 2010)
# Prevents the system from complaining
# about having too many connections open from
# the same IP. More info:
# http://www.linuxfocus.org/English/November2000/article175.shtml
}

mysqlchk.conf

start on socket PROTO=inet PORT=23066 ADDR=0.0.0.0
setuid nobody
exec /usr/bin/python3 /opt/tools/socket-handler.py /opt/tools/mysqlchk.sh

mysqlchk.sh

#!/bin/bash
#
# This script checks if a mysql server is healthy running on localhost. It will
# return:
# "HTTP/1.x 200 OK\r" (if mysql is running smoothly)
# - OR -
# "HTTP/1.x 500 Internal Server Error\r" (else)
#
# The purpose of this script is make haproxy capable of monitoring mysql properly
#

MYSQL_HOST="127.0.0.1"
MYSQL_PORT="3306"
MYSQL_USERNAME="cmon"
MYSQL_PASSWORD="…"
MYSQL_OPTS="-N -q -A"
FORCE_FAIL="/tmp/proxyoff"
MYSQL_BIN="$(which mysql)"
CHECK_QUERY="show global status where variable_name='wsrep_local_state'"

return_ok()
{
    printf "HTTP/1.1 200 OK\r\n"
sleep 0.05
    printf "Content-Type: text/plain\r\n"
#sleep 0.05
#    printf "Content-Length: 43\r\n"
sleep 0.05
    printf "\r\n"
sleep 0.05
    printf "Galera Cluster Node running and synced.\r\n"
sleep 0.05
    printf "\r\n"
    exit 0
}
return_fail()
{
    printf "HTTP/1.1 503 Service Unavailable\r\n"
sleep 0.05
    printf "Content-Type: text/plain\r\n"
sleep 0.05
    printf "Content-Length: 42\r\n"
sleep 0.05
    printf "\r\n"
sleep 0.05
    printf "Galera Cluster Node *down*.\r\n"
sleep 0.05
    printf "$STDERR" | sed -e 's/\n$/\r\n/'
sleep 0.05
    printf "\r\n"
sleep 0.05
    exit 1
}
if [ -f "$FORCE_FAIL" ]; then
        STDERR="$FORCE_FAIL found"
        return_fail;
fi
STDOUT=$( { STDERR=$($MYSQL_BIN $MYSQL_OPTS --host=$MYSQL_HOST --port=$MYSQL_PORT --user=$MYSQL_USERNAME --password=$MYSQL_PASSWORD -e "$CHECK_QUERY" 2>&1 1>&$out); } {out}>&1 )
if [ $? -ne 0 ]; then
        return_fail;
fi
status=`echo "$STDOUT" | awk '{print $2;}'`

if [ $status -ne 4 ]; then
   return_fail;
fi

return_ok;

# EOF

socket-handler.py

#!/usr/bin/python3
import os, socket, subprocess, sys

# Create the socket file descriptor from the the env var
sock_fd = socket.fromfd(int(os.environ["UPSTART_FDS"]),
                        socket.AF_INET, socket.SOCK_STREAM)

# Accept the connection, create a connection file descriptor
conn, addr = sock_fd.accept()

# Start the specified command and captue the output
# http://stackoverflow.com/questions/4760215/running-shell-command-from-python-and-capturing-the-output
output = subprocess.Popen(sys.argv[1:], stdout=subprocess.PIPE).communicate()[0]

# Write
#conn.send(output.decode('UTF-8'))
conn.send(output)

# Finish
conn.close()

# EOF