Stream: speed up TCP peer recovery. Previously, an unavailable peer was considered recovered after a successful proxy session to this peer. Until then, only a single client connection per fail_timeout was allowed to be proxied to the peer. Since stream sessions can be long, it may take indefinite time for a peer to recover, limiting the ability of the peer to receive new connections. Now, a peer is considered recovered after a successful TCP connection is established to it. Balancers are notified of this event via the notify() callback.

--- a/src/stream/ngx_stream_proxy_module.c
+++ b/src/stream/ngx_stream_proxy_module.c
@@ -808,6 +808,11 @@ ngx_stream_proxy_init_upstream(ngx_strea
 
     u->state->connect_time = ngx_current_msec - u->state->response_time;
 
+    if (u->peer.notify) {
+        u->peer.notify(&u->peer, u->peer.data,
+                       NGX_STREAM_UPSTREAM_NOTIFY_CONNECT);
+    }
+
     c->log->action = "proxying connection";
 
     if (u->upstream_buf.start == NULL) {