/* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "mod_proxy.h"
#include "scoreboard.h"
#include "ap_mpm.h"
#include "apr_version.h"
#include "ap_hooks.h"
module AP_MODULE_DECLARE_DATA lbmethod_byrequests_module;
static int (*ap_proxy_retry_worker_fn)(const char *proxy_function,
proxy_worker *worker, server_rec *s) = NULL;
/*
* The idea behind the find_best_byrequests scheduler is the following:
*
* lbfactor is "how much we expect this worker to work", or "the worker's
* normalized work quota".
*
* lbstatus is "how urgent this worker has to work to fulfill its quota
* of work".
*
* We distribute each worker's work quota to the worker, and then look
* which of them needs to work most urgently (biggest lbstatus). This
* worker is then selected for work, and its lbstatus reduced by the
* total work quota we distributed to all workers. Thus the sum of all
* lbstatus does not change.(*)
*
* If some workers are disabled, the others will
* still be scheduled correctly.
*
* If a balancer is configured as follows:
*
* worker a b c d
* lbfactor 25 25 25 25
*
* And b gets disabled, the following schedule is produced:
*
* a c d a c d a c d ...
*
* Note that the above lbfactor setting is the *exact* same as:
*
* worker a b c d
* lbfactor 1 1 1 1
*
* Asymmetric configurations work as one would expect. For
* example:
*
* worker a b c d
* lbfactor 1 1 1 2
*
* would have a, b and c all handling about the same
* amount of load with d handling twice what a or b
* or c handles individually. So we could see:
*
* b a d c d a c d b d ...
*
*/
static proxy_worker *find_best_byrequests(proxy_balancer *balancer,
request_rec *r)
{
int i;
int total_factor = 0;
proxy_worker **worker;
proxy_worker *mycandidate = NULL;
int cur_lbset = 0;
int max_lbset = 0;
int checking_standby;
int checked_standby;
if (!ap_proxy_retry_worker_fn) {
ap_proxy_retry_worker_fn =
APR_RETRIEVE_OPTIONAL_FN(ap_proxy_retry_worker);
if (!ap_proxy_retry_worker_fn) {
/* can only happen if mod_proxy isn't loaded */
return NULL;
}
}
ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server, APLOGNO(01207)
"proxy: Entering byrequests for BALANCER (%s)",
balancer->s->name);
/* First try to see if we have available candidate */
do {
checking_standby = checked_standby = 0;
while (!mycandidate && !checked_standby) {
worker = (proxy_worker **)balancer->workers->elts;
for (i = 0; i < balancer->workers->nelts; i++, worker++) {
if (!checking_standby) { /* first time through */
if ((*worker)->s->lbset > max_lbset)
max_lbset = (*worker)->s->lbset;
}
if (
((*worker)->s->lbset != cur_lbset) ||
(checking_standby ? !PROXY_WORKER_IS_STANDBY(*worker) : PROXY_WORKER_IS_STANDBY(*worker)) ||
(PROXY_WORKER_IS_DRAINING(*worker))
) {
continue;
}
/* If the worker is in error state run
* retry on that worker. It will be marked as
* operational if the retry timeout is elapsed.
* The worker might still be unusable, but we try
* anyway.
*/
if (!PROXY_WORKER_IS_USABLE(*worker))
ap_proxy_retry_worker_fn("BALANCER", *worker, r->server);
/* Take into calculation only the workers that are
* not in error state or not disabled.
*/
if (PROXY_WORKER_IS_USABLE(*worker)) {
(*worker)->s->lbstatus += (*worker)->s->lbfactor;
total_factor += (*worker)->s->lbfactor;
if (!mycandidate || (*worker)->s->lbstatus > mycandidate->s->lbstatus)
mycandidate = *worker;
}
}
checked_standby = checking_standby++;
}
cur_lbset++;
} while (cur_lbset <= max_lbset && !mycandidate);
if (mycandidate) {
mycandidate->s->lbstatus -= total_factor;
ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server, APLOGNO(01208)
"proxy: byrequests selected worker \"%s\" : busy %" APR_SIZE_T_FMT " : lbstatus %d",
mycandidate->s->name, mycandidate->s->busy, mycandidate->s->lbstatus);
}
return mycandidate;
}
/* assumed to be mutex protected by caller */
static apr_status_t reset(proxy_balancer *balancer, server_rec *s)
{
int i;
proxy_worker **worker;
worker = (proxy_worker **)balancer->workers->elts;
for (i = 0; i < balancer->workers->nelts; i++, worker++) {
(*worker)->s->lbstatus = 0;
}
return APR_SUCCESS;
}
static apr_status_t age(proxy_balancer *balancer, server_rec *s)
{
return APR_SUCCESS;
}
/*
* How to add additional lbmethods:
* 1. Create func which determines "best" candidate worker
* (eg: find_best_bytraffic, above)
* 2. Register it as a provider.
*/
static const proxy_balancer_method byrequests =
{
"byrequests",
&find_best_byrequests,
NULL,
&reset,
&age
};
static void register_hook(apr_pool_t *p)
{
/* Only the mpm_winnt has child init hook handler.
* make sure that we are called after the mpm
* initializes and after the mod_proxy
*/
ap_register_provider(p, PROXY_LBMETHOD, "byrequests", "0", &byrequests);
}
AP_DECLARE_MODULE(lbmethod_byrequests) = {
STANDARD20_MODULE_STUFF,
NULL, /* create per-directory config structure */
NULL, /* merge per-directory config structures */
NULL, /* create per-server config structure */
NULL, /* merge per-server config structures */
NULL, /* command apr_table_t */
register_hook /* register hooks */
};