netdata/netdata

#!/usr/bin/env bash

# SPDX-License-Identifier: GPL-3.0-or-later

# This is a simple exporting proxy, written in BASH, using the nc command.
# Run the script without any parameters for help.

MODE="${1}"
MY_PORT="${2}"
EXPORTING_HOST="${3}"
EXPORTING_PORT="${4}"
FILE="${NETDATA_NC_EXPORTING_DIR-/tmp}/netdata-nc-exporting-${MY_PORT}"

log() {
    logger --stderr --id=$$ --tag "netdata-nc-exporting" "${*}"
}

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_exporting_host="${3}" real_exporting_port="${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 "${file}" ]
            then
            if [ -n "${real_exporting_host}" ] && [ -n "${real_exporting_port}" ]
                then
                log "Attempting to send the metrics to the real external database at ${real_exporting_host}:${real_exporting_port}"
                
                mync "${real_exporting_host}" "${real_exporting_port}" <"${file}"
                ret=$?

                if [ ${ret} -eq 0 ]
                    then
                    log "Successfully sent the metrics to ${real_exporting_host}:${real_exporting_port}"
                    mv "${file}" "${file}.old"
                    touch "${file}"
                else
                    log "Failed to send the metrics to ${real_exporting_host}:${real_exporting_port} (nc returned ${ret}) - appending more data to ${file}"
                fi
            else
                log "No external database 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}" "${EXPORTING_HOST}" "${EXPORTING_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 [EXPORTING_HOST EXPORTING_PORT]

    PORT          The port this script will listen
                  (configure netdata to use this as an external database)

    EXPORTING_HOST  The real host for the external database
    EXPORTING_PORT  The real port for the external database

    This script can act as fallback database for netdata.
    It will receive metrics from netdata, save them to
    ${FILE}
    and once netdata reconnects to the real external database,
    this script will push all metrics collected to the real
    external database 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 [EXPORTING_HOST EXPORTING_PORT]
EOF
    exit 1
fi