nifi 启动流程

在启动脚本可以看到启动过程调用的是org.apache.nifi.bootstrap.RunNiFi：

main() {
    init "$1"
    run "$@"
}


case "$1" in
    install)
        install "$@"
        ;;
    start|stop|run|status|dump|diagnostics|env)
        main "$@"
        ;;

    #Note: Use of this command is considered experimental. The commands and approach used may change from time to time.
    stateless)
        stateless "$@"
        ;;
    restart)
        init
        run "stop"
        run "start"
        ;;
    *)
        echo "Usage nifi {start|stop|run|restart|status|dump|diagnostics|install|stateless}"
        ;;
esac


run() {
    BOOTSTRAP_CONF_DIR="${NIFI_HOME}/conf"
    BOOTSTRAP_CONF="${BOOTSTRAP_CONF_DIR}/bootstrap.conf";
    BOOTSTRAP_LIBS="${NIFI_HOME}/lib/bootstrap/*"

    run_as_user=$(grep '^\s*run.as' "${BOOTSTRAP_CONF}" | cut -d'=' -f2)
    # If the run as user is the same as that starting the process, ignore this configuration
    if [ "${run_as_user}" = "$(whoami)" ]; then
        unset run_as_user
    fi

    if $cygwin; then
        if [ -n "${run_as_user}" ]; then
            echo "The run.as option is not supported in a Cygwin environment. Exiting."
            exit 1
        fi;

        NIFI_HOME=$(cygpath --path --windows "${NIFI_HOME}")
        NIFI_LOG_DIR=$(cygpath --path --windows "${NIFI_LOG_DIR}")
        NIFI_PID_DIR=$(cygpath --path --windows "${NIFI_PID_DIR}")
        BOOTSTRAP_CONF=$(cygpath --path --windows "${BOOTSTRAP_CONF}")
        BOOTSTRAP_CONF_DIR=$(cygpath --path --windows "${BOOTSTRAP_CONF_DIR}")
        BOOTSTRAP_LIBS=$(cygpath --path --windows "${BOOTSTRAP_LIBS}")
        BOOTSTRAP_CLASSPATH="${BOOTSTRAP_CONF_DIR};${BOOTSTRAP_LIBS}"
        if [ -n "${TOOLS_JAR}" ]; then
            TOOLS_JAR=$(cygpath --path --windows "${TOOLS_JAR}")
            BOOTSTRAP_CLASSPATH="${TOOLS_JAR};${BOOTSTRAP_CLASSPATH}"
        fi
    else
        if [ -n "${run_as_user}" ]; then
            if ! id -u "${run_as_user}" >/dev/null 2>&1; then
                echo "The specified run.as user ${run_as_user} does not exist. Exiting."
                exit 1
            fi
        fi;
        BOOTSTRAP_CLASSPATH="${BOOTSTRAP_CONF_DIR}:${BOOTSTRAP_LIBS}"
        if [ -n "${TOOLS_JAR}" ]; then
            BOOTSTRAP_CLASSPATH="${TOOLS_JAR}:${BOOTSTRAP_CLASSPATH}"
        fi
    fi

    echo
    echo "Java home: ${JAVA_HOME}"
    echo "NiFi home: ${NIFI_HOME}"
    echo
    echo "Bootstrap Config File: ${BOOTSTRAP_CONF}"
    echo

    # run 'start' in the background because the process will continue to run, monitoring NiFi.
    # all other commands will terminate quickly so want to just wait for them

    #setup directory parameters
    BOOTSTRAP_LOG_PARAMS="-Dorg.apache.nifi.bootstrap.config.log.dir='${NIFI_LOG_DIR}'"
    BOOTSTRAP_PID_PARAMS="-Dorg.apache.nifi.bootstrap.config.pid.dir='${NIFI_PID_DIR}'"
    BOOTSTRAP_CONF_PARAMS="-Dorg.apache.nifi.bootstrap.config.file='${BOOTSTRAP_CONF}'"

    # uncomment to allow debugging of the bootstrap process
    #BOOTSTRAP_DEBUG_PARAMS="-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=8000"

    BOOTSTRAP_DIR_PARAMS="${BOOTSTRAP_LOG_PARAMS} ${BOOTSTRAP_PID_PARAMS} ${BOOTSTRAP_CONF_PARAMS}"

    run_nifi_cmd="'${JAVA}' -cp '${BOOTSTRAP_CLASSPATH}' -Xms12m -Xmx24m ${BOOTSTRAP_DIR_PARAMS} ${BOOTSTRAP_DEBUG_PARAMS} ${BOOTSTRAP_JAVA_OPTS} org.apache.nifi.bootstrap.RunNiFi $@"

    if [ -n "${run_as_user}" ]; then
      # Provide SCRIPT_DIR and execute nifi-env for the run.as user command
      run_nifi_cmd="sudo -u ${run_as_user} sh -c \"SCRIPT_DIR='${SCRIPT_DIR}' && . '${SCRIPT_DIR}/nifi-env.sh' && ${run_nifi_cmd}\""
    fi

    if [ "$1" = "run" ]; then
      # Use exec to handover PID to RunNiFi java process, instead of foking it as a child process
      run_nifi_cmd="exec ${run_nifi_cmd}"
    fi

    if [ "$1" = "start" ]; then
        ( eval "cd ${NIFI_HOME} && ${run_nifi_cmd}" & )> /dev/null 1>&-
    else
        eval "cd ${NIFI_HOME} && ${run_nifi_cmd}"
    fi
    EXIT_STATUS=$?

    # Wait just a bit (3 secs) to wait for the logging to finish and then echo a new-line.
    # We do this to avoid having logs spewed on the console after running the command and then not giving
    # control back to the user
    sleep 3
    echo
}