Upstream: added sticky sessions support for upstreams.

Sticky sessions allow to route the same client to the same upstream server.

- upstream structures are extended to keep session-related information

- existing balancing modules are updated to provide an id of the selected
  server (SID) in pc->sid, and to select the server, given it's SID.

- other balancing modules are allowed to set the pc->hint value to choose
  the desired peer.  The sticky module will not change the hint if it's
  already set.

- the feature is enabled by default and can be disabled with the
  "--without-http_upstream_sticky" switch of the configure script.

The following configuration can be used to enable sticky sessions for
supported balancing modules:

    upstream u1 {
        server 127.0.0.1:8080;
        server 127.0.0.1:8081;

        sticky cookie server_id expires=1h domain=.example.com path=/;
    }

Co-authored-by: Ruslan Ermilov <ru@nginx.com>
Co-authored-by: Roman Arutyunyan <arut@nginx.com>
Co-authored-by: Maxim Dounin <mdounin@mdounin.ru>

1 files changed, 38 insertions, 0 deletions

diff --git a/src/http/modules/ngx_http_upstream_random_module.c b/src/http/modules/ngx_http_upstream_random_module.c
index 74714874b..72885cde8 100644
--- a/src/http/modules/ngx_http_upstream_random_module.c
+++ b/src/http/modules/ngx_http_upstream_random_module.c
@@ -249,6 +249,17 @@ ngx_http_upstream_get_random_peer(ngx_peer_connection_t *pc, void *data)
 
     now = ngx_time();
 
+#if (NGX_HTTP_UPSTREAM_SID)
+    peer = ngx_http_upstream_get_rr_peer_by_sid(rrp, pc->hint, &i, 1);
+
+    if (peer) {
+        n = i / (8 * sizeof(uintptr_t));
+        m = (uintptr_t) 1 << i % (8 * sizeof(uintptr_t));
+
+        goto found;
+    }
+#endif
+
     for ( ;; ) {
 
         i = ngx_http_upstream_peek_random_peer(peers, rp);
@@ -292,6 +303,10 @@ ngx_http_upstream_get_random_peer(ngx_peer_connection_t *pc, void *data)
         }
     }
 
+#if (NGX_HTTP_UPSTREAM_SID)
+found:
+#endif
+
     rrp->current = peer;
     ngx_http_upstream_rr_peer_ref(peers, peer);
 
@@ -303,6 +318,10 @@ ngx_http_upstream_get_random_peer(ngx_peer_connection_t *pc, void *data)
     pc->socklen = peer->socklen;
     pc->name = &peer->name;
 
+#if (NGX_HTTP_UPSTREAM_SID)
+    pc->sid = &peer->sid;
+#endif
+
     peer->conns++;
 
     ngx_http_upstream_rr_peer_unlock(peers, peer);
@@ -357,6 +376,17 @@ ngx_http_upstream_get_random2_peer(ngx_peer_connection_t *pc, void *data)
     p = 0;
 #endif
 
+#if (NGX_HTTP_UPSTREAM_SID)
+    peer = ngx_http_upstream_get_rr_peer_by_sid(rrp, pc->hint, &i, 0);
+
+    if (peer) {
+        n = i / (8 * sizeof(uintptr_t));
+        m = (uintptr_t) 1 << i % (8 * sizeof(uintptr_t));
+
+        goto found;
+    }
+#endif
+
     for ( ;; ) {
 
         i = ngx_http_upstream_peek_random_peer(peers, rp);
@@ -410,6 +440,10 @@ ngx_http_upstream_get_random2_peer(ngx_peer_connection_t *pc, void *data)
         }
     }
 
+#if (NGX_HTTP_UPSTREAM_SID)
+found:
+#endif
+
     rrp->current = peer;
     ngx_http_upstream_rr_peer_ref(peers, peer);
 
@@ -421,6 +455,10 @@ ngx_http_upstream_get_random2_peer(ngx_peer_connection_t *pc, void *data)
     pc->socklen = peer->socklen;
     pc->name = &peer->name;
 
+#if (NGX_HTTP_UPSTREAM_SID)
+    pc->sid = &peer->sid;
+#endif
+
     peer->conns++;
 
     ngx_http_upstream_rr_peers_unlock(peers);