/* Part of ClioPatria SeRQL and SPARQL server Author: Jan Wielemaker E-mail: J.Wielemaker@cs.vu.nl WWW: http://www.swi-prolog.org Copyright (C): 2010, University of Amsterdam, VU University Amsterdam This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA As a special exception, if you link this library with other files, compiled with a Free Software compiler, to produce an executable, this library does not by itself cause the resulting executable to be covered by the GNU General Public License. This exception does not however invalidate any other reasons why the executable file might be covered by the GNU General Public License. */ :- module(http_monitor, [ http_monitor/1 % +Options ]). :- use_module(library(http/http_open)). :- use_module(library(http/thread_httpd)). :- use_module(library(unix)). :- use_module(library(time)). :- use_module(library(option)). :- use_module(library(error)). :- use_module(library(debug)). :- use_module(library(readutil)). /** Monitor an HTTP servers health status This module monitors an HTTP server and kills it if it proves to be in a bad state for some time. */ :- dynamic options/1, % Options started_at/1, % Stamp failures/1. % Current failure count %% http_monitor(+Options) is det. % % Monitor an HTTP service. Options: % % * fork(+Bool) % If =true=, fork and monitor the parent process. Unix only. % % * pid(+PID) % The PID of the monitored process. This process is killed if % it fails to respond % % * interval(+Seconds) % Polling interval. Default is to poll every 20 seconds. % % * max_failures(+Count) % Terminate the monitored service after Count failed connects. % Default is 3 times. % % * max_start_time(+Time) % Max time we consider 503 status acceptable. % % * max_wait(+Wait) % Max time to wait for a reply. Default is 10 seconds. % % * url(URL) % URL to poll. Default is =|http://localhost:/|= http_monitor(Options) :- select_option(fork(true), Options, Options1), !, current_prolog_flag(pid, Monitored), fork(Pid), ( Pid == client -> http_monitor([pid(Monitored)|Options1]) ; print_message(informational, http_monitor(forked(Pid))) ). http_monitor(Options) :- setup_monitor(Options), get_time(Now), assert(started_at(Now)), option(interval(Time), Options, 20), repeat, catch(check(Options), E, ( print_message(error, E), halt(1))), sleep(Time), fail. setup_monitor(Options) :- assert(options(Options)), on_signal(int, _, signal_handler), on_signal(hup, _, signal_handler). signal_handler(int) :- halt. signal_handler(hup) :- options(Options), check(Options). check(Options) :- monitor_url(Options, URL), option(max_wait(Limit), Options, 10), get_time(Start), ( catch(call_with_time_limit(Limit, guarded_check(URL, Options)), E, true) -> get_time(Now), Time is Now - Start, ( var(E) -> debug(http_monitor, '200 OK in ~3f sec', [Time]), retractall(failures(_)) ; act(E, URL, Options) ) ; act(failed, URL, Options) ). monitor_url(Options, URL) :- option(url(URL), Options), !. monitor_url(_, URL) :- http_current_server(_Pred, Port), format(atom(URL), 'http://localhost:~w/', [Port]). guarded_check(URL, Options) :- http_open(URL, In, Options), call_cleanup(read_stream_to_codes(In, _Codes), close(In)). act(error(_, context(status(Code, Comment))), URL, Options) :- !, print_message(warning, http_monitor(error(Code-Comment, URL))), step_error(Code, Options). act(What, URL, Options) :- print_message(warning, http_monitor(error(What, URL))), step_error(0, Options). step_error(503, Options) :- !, % unavailable: startup started_at(Start), get_time(Now), Starting is Now - Start, option(max_start_time(MaxStart), Options, 300), ( Starting < MaxStart -> true ; print_message(error, http_monitor(start_failed(MaxStart))), kill_server(Options) ). step_error(_, Options) :- ( retract(failures(C0)) -> true ; C0 = 0 ), C1 is C0+1, assert(failures(C1)), option(max_failures(Max), Options, 3), C1 > Max, print_message(error, http_monitor(no_response(Max))), kill_server(Options). %% kill_server(+Options) is semidet. % % Kill the server. kill_server(Options) :- option(pid(Pid), Options), !, between(1, 10, Try), signal_for_try(Try, Sig), print_message(informational, http_monitor(kill(Pid, Sig))), catch(kill(Pid, Sig), E, Done=true), ( Done == true -> ( E = error(existence_error(process, Pid), _) -> ! ; throw(E) ) ; sleep(10), fail ). kill_server(_Options) :- existence_error(option, pid). signal_for_try(Try, Sig) :- ( Try < 3 -> Sig = int ; Try < 5 -> Sig = term ; Sig = kill ). /******************************* * MESSAGES * *******************************/ :- multifile prolog:message//1. prolog:message(http_monitor(Message)) --> message(Message). message(forked(PID)) --> [ 'Forked monitor process; PID=~w'-[PID] ]. message(kill(Pid, Signal)) --> [ 'Killing ~w using signal ~w'-[Pid, Signal] ]. message(error(Code-Comment, URL)) --> [ '~w: ~w (~w)'-[URL, Code, Comment] ]. message(error(Error, URL)) --> [ '~w: ~w'-[URL, Error] ]. message(start_failed(MaxTime)) --> [ 'Server claims 503 status for more than ~w seconds: killing'-[MaxTime] ]. message(no_response(Max)) --> [ 'Server failed to respond more than ~w times in a row: killing'-[Max] ].