HTTP/2: allow unlimited number of requests in connection

[Michael Würtinger]

Hello,

we're running a gRPC service behind an NGINX load balancer and we
often see that the connection gets shut down with a GOAWAY message.
Since our request deadlines are quite small and it takes some time to
re-establish a connection this often leads to many failed requests.

After analyzing the situation we realized that it is caused by the
"http2_max_requests" option which defaults to 1000. After setting this
to a ridiculously high value our problems disappeared.

While there probably are use cases where limiting the life time of a
connection makes sense we were wondering why it is not possible to
disable this functionality and let a connection just live as long as
possible?

The following patch allows to do just that by setting http2_max_requests to 0.

Please let me know what you think.

Thanks,
Michael

# HG changeset patch
# User Michael Würtinger <michael.wuertinger at egym.com>
# Date 1561569724 -7200
#      Wed Jun 26 19:22:04 2019 +0200
# Node ID d703d79897320bfc743b2ea6421e301985b2c7e4
# Parent  35ea9229c71a9207a24e51f327e1749e3accb26c
HTTP/2: allow unlimited number of requests in connection

Allows to disable the "http2_max_requests" limit by setting it to 0. This
enables very long living HTTP/2 connections which is desirable for some
use cases like gRPC connections.

diff -r 35ea9229c71a -r d703d7989732 src/http/v2/ngx_http_v2.c
--- a/src/http/v2/ngx_http_v2.c Tue Jun 25 15:19:45 2019 +0300
+++ b/src/http/v2/ngx_http_v2.c Wed Jun 26 19:22:04 2019 +0200
@@ -1173,7 +1173,9 @@
        ngx_http_v2_set_dependency(h2c, node, depend, excl);
    }

-    if (h2c->connection->requests >= h2scf->max_requests) {
+    if (h2scf->max_requests > 0
+        && h2c->connection->requests >= h2scf->max_requests)
+    {
        h2c->goaway = 1;

        if (ngx_http_v2_send_goaway(h2c, NGX_HTTP_V2_NO_ERROR) == NGX_ERROR) {
@@ -4514,7 +4516,7 @@
    h2scf = ngx_http_get_module_srv_conf(h2c->http_connection->conf_ctx,
                                         ngx_http_v2_module);

-    if (h2c->idle++ > 10 * h2scf->max_requests) {
+    if (h2c->idle++ > 10 * h2scf->max_requests && h2scf->max_requests > 0) {
        ngx_log_error(NGX_LOG_INFO, h2c->connection->log, 0,
                      "http2 flood detected");
        ngx_http_v2_finalize_connection(h2c, NGX_HTTP_V2_NO_ERROR);

-- 
 <https://egym.com>