Upstream: re-resolvable servers.

Specifying the upstream server by a hostname together with the
"resolve" parameter will make the hostname to be periodically
resolved, and upstream servers added/removed as necessary.

This requires a "resolver" at the "http" configuration block.

The "resolver_timeout" parameter also affects when the failed
DNS requests will be attempted again.  Responses with NXDOMAIN
will be attempted again in 10 seconds.

Upstream has a configuration generation number that is incremented each
time servers are added/removed to the primary/backup list.  This number
is remembered by the peer.init method, and if peer.get detects a change
in configuration, it returns NGX_BUSY.

Each server has a reference counter.  It is incremented by peer.get and
decremented by peer.free.  When a server is removed, it is removed from
the list of servers and is marked as "zombie".  The memory allocated by
a zombie peer is freed only when its reference count becomes zero.

Co-authored-by: Roman Arutyunyan <arut@nginx.com>
Co-authored-by: Sergey Kandaurov <pluknet@nginx.com>
Co-authored-by: Vladimir Homutov <vl@nginx.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/http/modules/ngx_http_upstream_least_conn_module.c b/src/http/modules/ngx_http_upstream_least_conn_module.c
index ebe06276d..4df97777c 100644
--- a/src/http/modules/ngx_http_upstream_least_conn_module.c
+++ b/src/http/modules/ngx_http_upstream_least_conn_module.c
@@ -124,6 +124,12 @@ ngx_http_upstream_get_least_conn_peer(ngx_peer_connection_t *pc, void *data)
 
     ngx_http_upstream_rr_peers_wlock(peers);
 
+#if (NGX_HTTP_UPSTREAM_ZONE)
+    if (peers->config && rrp->config != *peers->config) {
+        goto busy;
+    }
+#endif
+
     best = NULL;
     total = 0;
 
@@ -244,6 +250,7 @@ ngx_http_upstream_get_least_conn_peer(ngx_peer_connection_t *pc, void *data)
     best->conns++;
 
     rrp->current = best;
+    ngx_http_upstream_rr_peer_ref(peers, best);
 
     n = p / (8 * sizeof(uintptr_t));
     m = (uintptr_t) 1 << p % (8 * sizeof(uintptr_t));
@@ -280,6 +287,10 @@ failed:
         ngx_http_upstream_rr_peers_wlock(peers);
     }
 
+#if (NGX_HTTP_UPSTREAM_ZONE)
+busy:
+#endif
+
     ngx_http_upstream_rr_peers_unlock(peers);
 
     pc->name = peers->name;
@@ -303,6 +314,7 @@ ngx_http_upstream_least_conn(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
     uscf->peer.init_upstream = ngx_http_upstream_init_least_conn;
 
     uscf->flags = NGX_HTTP_UPSTREAM_CREATE
+                  |NGX_HTTP_UPSTREAM_MODIFY
                   |NGX_HTTP_UPSTREAM_WEIGHT
                   |NGX_HTTP_UPSTREAM_MAX_CONNS
                   |NGX_HTTP_UPSTREAM_MAX_FAILS