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#!/usr/bin/env bash
# SPDX-License-Identifier: GPL-3.0-or-later
# This is a simple backend database proxy, written in BASH, using the nc command.
# Run the script without any parameters for help.
MODE="${1}"
MY_PORT="${2}"
BACKEND_HOST="${3}"
BACKEND_PORT="${4}"
FILE="${NETDATA_NC_BACKEND_DIR-/tmp}/netdata-nc-backend-${MY_PORT}"
log() {
logger --stderr --id=$$ --tag "netdata-nc-backend" "${*}"
}
mync() {
local ret
log "Running: nc ${*}"
nc "${@}"
ret=$?
log "nc stopped with return code ${ret}."
return ${ret}
}
listen_save_replay_forever() {
local file="${1}" port="${2}" real_backend_host="${3}" real_backend_port="${4}" ret delay=1 started ended
while true
do
log "Starting nc to listen on port ${port} and save metrics to ${file}"
started=$(date +%s)
mync -l -p "${port}" | tee -a -p --output-error=exit "${file}"
ended=$(date +%s)
if [ -s "${file}" ]
then
if [ ! -z "${real_backend_host}" ] && [ ! -z "${real_backend_port}" ]
then
log "Attempting to send the metrics to the real backend at ${real_backend_host}:${real_backend_port}"
mync "${real_backend_host}" "${real_backend_port}" <"${file}"
ret=$?
if [ ${ret} -eq 0 ]
then
log "Successfully sent the metrics to ${real_backend_host}:${real_backend_port}"
mv "${file}" "${file}.old"
touch "${file}"
else
log "Failed to send the metrics to ${real_backend_host}:${real_backend_port} (nc returned ${ret}) - appending more data to ${file}"
fi
else
log "No backend configured - appending more data to ${file}"
fi
fi
# prevent a CPU hungry infinite loop
# if nc cannot listen to port
if [ $((ended - started)) -lt 5 ]
then
log "nc has been stopped too fast."
delay=30
else
delay=1
fi
log "Waiting ${delay} seconds before listening again for data."
sleep ${delay}
done
}
if [ "${MODE}" = "start" ]
then
# start the listener, in exclusive mode
# only one can use the same file/port at a time
{
flock -n 9
# shellcheck disable=SC2181
if [ $? -ne 0 ]
then
log "Cannot get exclusive lock on file ${FILE}.lock - Am I running multiple times?"
exit 2
fi
# save our PID to the lock file
echo "$$" >"${FILE}.lock"
listen_save_replay_forever "${FILE}" "${MY_PORT}" "${BACKEND_HOST}" "${BACKEND_PORT}"
ret=$?
log "listener exited."
exit ${ret}
} 9>>"${FILE}.lock"
# we can only get here if ${FILE}.lock cannot be created
log "Cannot create file ${FILE}."
exit 3
elif [ "${MODE}" = "stop" ]
then
{
flock -n 9
# shellcheck disable=SC2181
if [ $? -ne 0 ]
then
pid=$(<"${FILE}".lock)
log "Killing process ${pid}..."
kill -TERM "-${pid}"
exit 0
fi
log "File ${FILE}.lock has been locked by me but it shouldn't. Is a collector running?"
exit 4
} 9<"${FILE}.lock"
log "File ${FILE}.lock does not exist. Is a collector running?"
exit 5
else
cat <<EOF
Usage:
"${0}" start|stop PORT [BACKEND_HOST BACKEND_PORT]
PORT The port this script will listen
(configure netdata to use this as a second backend)
BACKEND_HOST The real backend host
BACKEND_PORT The real backend port
This script can act as fallback backend for netdata.
It will receive metrics from netdata, save them to
${FILE}
and once netdata reconnects to the real-backend, this script
will push all metrics collected to the real-backend too and
wait for a failure to happen again.
Only one netdata can connect to this script at a time.
If you need fallback for multiple netdata, run this script
multiple times with different ports.
You can run me in the background with this:
screen -d -m "${0}" start PORT [BACKEND_HOST BACKEND_PORT]
EOF
exit 1
fi
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