educational purpouses: describe how autoregistration works

mock-autoreg-event

#!/usr/bin/env bash

#
# Copyright note:
# ---------------
#
# This script is a modification from:
#   https://support.zabbix.com/secure/attachment/49385/get.sh
# written by gleb@irc#zabbix
#

# The script will connect to the zabbix server trapper port (default: 10051)
# in order to retrieve the list of active checks. But zabbix, behind the scenes
# will also fire an autoregistration event if the conditions are met.
# For more information please take a look at:
#
#   https://www.zabbix.com/documentation/3.2/manual/discovery/auto_registration
#
# Despite that we are asking for active checks in the request, we want to
# fire the auto-registration event. That's the main idea of this script.

# Zabbix is expecting something like: <HEADER><DATALEN><DATA> where:
# <HEADER>  := ZBXD\x01
# <DATALEN> := <little-endian-64bit-hex-value>
# <DATA>    := <json-object-defining-the-request>
#
# Asciially:
# 
# +---+---+---+---+----+----+----+----+----+----+----+----+----+-----------------+
# | Z | B | X | D | 01 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | ............... |
# +---+---+---+---+----+----+----+----+----+----+----+----+----+-----------------+
# \____________________/\______________________________________/\________________/
#     HEADER (5 bytes)           DATALEN (8 bytes)               DATA (max: 128MB)
#
#
# <DATALEN> must be the lenght of the <DATA> segment as 64bit HEX little endian byte order.
#

if [[ $# -lt 2 || $# -gt 3 ]]; then
    echo
    echo "Usage: $0 { <zabbix-host-name> <zabbix-server> } [ <zabbix-trapper-port> ]"
    echo
    exit 1
fi

# The hostname we are trying to mock auto-registration
ZBX_HOST=$1

# Zabbix server host/ip
ZBX_SERVER=$2

# Zabbix server trapper port (defaults to 10051)
ZBX_TRAPPER_PORT=${3:-10051}

# <HEADER> value as explained above
HEADER="ZBXD\\1"

# <DATA> content as explained above.
#
# We don't check for ZBX_HOST to be empty. Either way if wrong or empty
# the request will be OK, but no information may be displayed.
DATA="{\"request\": \"active checks\", \"host\": \"${ZBX_HOST}\"}"

# <DATALEN> as explained above.
#
# Create 64bit HEX little endian value equals to the size in bytes of DATA
DATALEN=$(printf '%016x' "${#DATA}" | \
    awk '{ r=""; for( i=length($0)-1; i > 0; i=i-2) r=r "\\x" substr($0, i, 2); print r}')

# Awesome work by gleb:
# Create connection
exec 3<>/dev/tcp/$ZBX_SERVER/$ZBX_TRAPPER_PORT

# Print to file descriptor 3. That was created in the above line.
printf "%b%b%s" "${HEADER}" "${DATALEN}" "${DATA}" >&3

# output the result skipping 5 bytes of "ZBXD\\1" header and 8 bytes of message length
RESPONSE=$(tail -c+13 <&3)

# If python is installed and python version supports/has json module make it human-readable
$(python -c "import json" 2> /dev/null) &&  echo ${RESPONSE} | python -mjson.tool

# If no python or json module exists...
if [ $? -ne 0 ]; then
    # just print the response
    echo ${RESPONSE}
fi

# Closes file descriptor
exec 3>&-
exec 3<&-