Core: added a warning about reusing connections.

Previously, reusing connections happened silently and was only
visible in monitoring systems.  This was shown to be not very user-friendly,
and administrators often didn't realize there were too few connections
available to withstand the load, and configured timeouts (keepalive_timeout
and http2_idle_timeout) were effectively reduced to keep things running.

To provide at least some information about this, a warning is now logged
(at most once per second, to avoid flooding the logs).

1 files changed, 1 insertions, 0 deletions

diff --git a/src/core/ngx_cycle.h b/src/core/ngx_cycle.h
index 54fa2e6bf..0f7d9bc74 100644
--- a/src/core/ngx_cycle.h
+++ b/src/core/ngx_cycle.h
@@ -55,6 +55,7 @@ struct ngx_cycle_s {
 
     ngx_queue_t               reusable_connections_queue;
     ngx_uint_t                reusable_connections_n;
+    time_t                    connections_reuse_time;
 
     ngx_array_t               listening;
     ngx_array_t               paths;