1/* Licensed to the Apache Software Foundation (ASF) under one or more
2 * contributor license agreements.  See the NOTICE file distributed with
3 * this work for additional information regarding copyright ownership.
4 * The ASF licenses this file to You under the Apache License, Version 2.0
5 * (the "License"); you may not use this file except in compliance with
6 * the License.  You may obtain a copy of the License at
7 *
8 *     http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#include "mod_proxy.h"
18#include "scoreboard.h"
19#include "ap_mpm.h"
20#include "apr_version.h"
21#include "ap_hooks.h"
22
23module AP_MODULE_DECLARE_DATA lbmethod_byrequests_module;
24
25static int (*ap_proxy_retry_worker_fn)(const char *proxy_function,
26        proxy_worker *worker, server_rec *s) = NULL;
27
28/*
29 * The idea behind the find_best_byrequests scheduler is the following:
30 *
31 * lbfactor is "how much we expect this worker to work", or "the worker's
32 * normalized work quota".
33 *
34 * lbstatus is "how urgent this worker has to work to fulfill its quota
35 * of work".
36 *
37 * We distribute each worker's work quota to the worker, and then look
38 * which of them needs to work most urgently (biggest lbstatus).  This
39 * worker is then selected for work, and its lbstatus reduced by the
40 * total work quota we distributed to all workers.  Thus the sum of all
41 * lbstatus does not change.(*)
42 *
43 * If some workers are disabled, the others will
44 * still be scheduled correctly.
45 *
46 * If a balancer is configured as follows:
47 *
48 * worker     a    b    c    d
49 * lbfactor  25   25   25   25
50 *
51 * And b gets disabled, the following schedule is produced:
52 *
53 *    a c d a c d a c d ...
54 *
55 * Note that the above lbfactor setting is the *exact* same as:
56 *
57 * worker     a    b    c    d
58 * lbfactor   1    1    1    1
59 *
60 * Asymmetric configurations work as one would expect. For
61 * example:
62 *
63 * worker     a    b    c    d
64 * lbfactor   1    1    1    2
65 *
66 * would have a, b and c all handling about the same
67 * amount of load with d handling twice what a or b
68 * or c handles individually. So we could see:
69 *
70 *   b a d c d a c d b d ...
71 *
72 */
73
74static proxy_worker *find_best_byrequests(proxy_balancer *balancer,
75                                request_rec *r)
76{
77    int i;
78    int total_factor = 0;
79    proxy_worker **worker;
80    proxy_worker *mycandidate = NULL;
81    int cur_lbset = 0;
82    int max_lbset = 0;
83    int checking_standby;
84    int checked_standby;
85
86    if (!ap_proxy_retry_worker_fn) {
87        ap_proxy_retry_worker_fn =
88                APR_RETRIEVE_OPTIONAL_FN(ap_proxy_retry_worker);
89        if (!ap_proxy_retry_worker_fn) {
90            /* can only happen if mod_proxy isn't loaded */
91            return NULL;
92        }
93    }
94
95    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server, APLOGNO(01207)
96                 "proxy: Entering byrequests for BALANCER (%s)",
97                 balancer->s->name);
98
99    /* First try to see if we have available candidate */
100    do {
101        checking_standby = checked_standby = 0;
102        while (!mycandidate && !checked_standby) {
103            worker = (proxy_worker **)balancer->workers->elts;
104            for (i = 0; i < balancer->workers->nelts; i++, worker++) {
105                if (!checking_standby) {    /* first time through */
106                    if ((*worker)->s->lbset > max_lbset)
107                        max_lbset = (*worker)->s->lbset;
108                }
109                if (
110                    ((*worker)->s->lbset != cur_lbset) ||
111                    (checking_standby ? !PROXY_WORKER_IS_STANDBY(*worker) : PROXY_WORKER_IS_STANDBY(*worker)) ||
112                    (PROXY_WORKER_IS_DRAINING(*worker))
113                    ) {
114                    continue;
115                }
116
117                /* If the worker is in error state run
118                 * retry on that worker. It will be marked as
119                 * operational if the retry timeout is elapsed.
120                 * The worker might still be unusable, but we try
121                 * anyway.
122                 */
123                if (!PROXY_WORKER_IS_USABLE(*worker))
124                    ap_proxy_retry_worker_fn("BALANCER", *worker, r->server);
125                /* Take into calculation only the workers that are
126                 * not in error state or not disabled.
127                 */
128                if (PROXY_WORKER_IS_USABLE(*worker)) {
129                    (*worker)->s->lbstatus += (*worker)->s->lbfactor;
130                    total_factor += (*worker)->s->lbfactor;
131                    if (!mycandidate || (*worker)->s->lbstatus > mycandidate->s->lbstatus)
132                        mycandidate = *worker;
133                }
134            }
135            checked_standby = checking_standby++;
136        }
137        cur_lbset++;
138    } while (cur_lbset <= max_lbset && !mycandidate);
139
140    if (mycandidate) {
141        mycandidate->s->lbstatus -= total_factor;
142        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server, APLOGNO(01208)
143                     "proxy: byrequests selected worker \"%s\" : busy %" APR_SIZE_T_FMT " : lbstatus %d",
144                     mycandidate->s->name, mycandidate->s->busy, mycandidate->s->lbstatus);
145
146    }
147
148    return mycandidate;
149}
150
151/* assumed to be mutex protected by caller */
152static apr_status_t reset(proxy_balancer *balancer, server_rec *s) {
153    int i;
154    proxy_worker **worker;
155    worker = (proxy_worker **)balancer->workers->elts;
156    for (i = 0; i < balancer->workers->nelts; i++, worker++) {
157        (*worker)->s->lbstatus = 0;
158    }
159    return APR_SUCCESS;
160}
161
162static apr_status_t age(proxy_balancer *balancer, server_rec *s) {
163        return APR_SUCCESS;
164}
165
166/*
167 * How to add additional lbmethods:
168 *   1. Create func which determines "best" candidate worker
169 *      (eg: find_best_bytraffic, above)
170 *   2. Register it as a provider.
171 */
172static const proxy_balancer_method byrequests =
173{
174    "byrequests",
175    &find_best_byrequests,
176    NULL,
177    &reset,
178    &age
179};
180
181static void register_hook(apr_pool_t *p)
182{
183    /* Only the mpm_winnt has child init hook handler.
184     * make sure that we are called after the mpm
185     * initializes and after the mod_proxy
186     */
187    ap_register_provider(p, PROXY_LBMETHOD, "byrequests", "0", &byrequests);
188}
189
190AP_DECLARE_MODULE(lbmethod_byrequests) = {
191    STANDARD20_MODULE_STUFF,
192    NULL,       /* create per-directory config structure */
193    NULL,       /* merge per-directory config structures */
194    NULL,       /* create per-server config structure */
195    NULL,       /* merge per-server config structures */
196    NULL,       /* command apr_table_t */
197    register_hook /* register hooks */
198};
199