[nginx] Changed keepalive_requests default to 1000 (ticket #2155).

[Maxim Dounin]

details:   https://hg.nginx.org/nginx/rev/82e174e47663
branches:  
changeset: 7822:82e174e47663
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Thu Apr 08 00:16:30 2021 +0300
description:
Changed keepalive_requests default to 1000 (ticket #2155).

It turns out no browsers implement HTTP/2 GOAWAY handling properly, and
large enough number of resources on a page results in failures to load
some resources.  In particular, Chrome seems to experience errors if
loading of all resources requires more than 1 connection (while it
is usually able to retry requests at least once, even with 2 connections
there are occasional failures for some reason), Safari if loading requires
more than 3 connections, and Firefox if loading requires more than 10
connections (can be configured with network.http.request.max-attempts,
defaults to 10).

It does not seem to be possible to resolve this on nginx side, even strict
limiting of maximum concurrency does not help, and loading issues seems to
be triggered by merely queueing of a request for a particular connection.
The only available mitigation seems to use higher keepalive_requests value.

The new default is 1000 and matches previously used default for
http2_max_requests.  It is expected to be enough for 99.98% of the pages
(https://httparchive.org/reports/state-of-the-web?start=latest#reqTotal)
even in Chrome.

diffstat:

 src/http/modules/ngx_http_upstream_keepalive_module.c |  2 +-
 src/http/ngx_http_core_module.c                       |  2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diffs (24 lines):

diff -r 6d4f7d5e279f -r 82e174e47663 src/http/modules/ngx_http_upstream_keepalive_module.c
--- a/src/http/modules/ngx_http_upstream_keepalive_module.c	Thu Apr 08 00:16:17 2021 +0300
+++ b/src/http/modules/ngx_http_upstream_keepalive_module.c	Thu Apr 08 00:16:30 2021 +0300
@@ -159,7 +159,7 @@ ngx_http_upstream_init_keepalive(ngx_con
 
     ngx_conf_init_msec_value(kcf->time, 3600000);
     ngx_conf_init_msec_value(kcf->timeout, 60000);
-    ngx_conf_init_uint_value(kcf->requests, 100);
+    ngx_conf_init_uint_value(kcf->requests, 1000);
 
     if (kcf->original_init_upstream(cf, us) != NGX_OK) {
         return NGX_ERROR;
diff -r 6d4f7d5e279f -r 82e174e47663 src/http/ngx_http_core_module.c
--- a/src/http/ngx_http_core_module.c	Thu Apr 08 00:16:17 2021 +0300
+++ b/src/http/ngx_http_core_module.c	Thu Apr 08 00:16:30 2021 +0300
@@ -3758,7 +3758,7 @@ ngx_http_core_merge_loc_conf(ngx_conf_t 
     ngx_conf_merge_sec_value(conf->keepalive_header,
                               prev->keepalive_header, 0);
     ngx_conf_merge_uint_value(conf->keepalive_requests,
-                              prev->keepalive_requests, 100);
+                              prev->keepalive_requests, 1000);
     ngx_conf_merge_uint_value(conf->lingering_close,
                               prev->lingering_close, NGX_HTTP_LINGERING_ON);
     ngx_conf_merge_msec_value(conf->lingering_time,