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, 8 insertions, 1 deletions

diff --git a/src/http/ngx_http_upstream.h b/src/http/ngx_http_upstream.h
index db0e1424e..0922021bd 100644
--- a/src/http/ngx_http_upstream.h
+++ b/src/http/ngx_http_upstream.h
@@ -104,7 +104,11 @@ typedef struct {
 
     unsigned                         backup:1;
 
-    NGX_COMPAT_BEGIN(6)
+#if (NGX_HTTP_UPSTREAM_ZONE)
+    ngx_str_t                        host;
+#endif
+
+    NGX_COMPAT_BEGIN(4)
     NGX_COMPAT_END
 } ngx_http_upstream_server_t;
 
@@ -115,6 +119,7 @@ typedef struct {
 #define NGX_HTTP_UPSTREAM_FAIL_TIMEOUT  0x0008
 #define NGX_HTTP_UPSTREAM_DOWN          0x0010
 #define NGX_HTTP_UPSTREAM_BACKUP        0x0020
+#define NGX_HTTP_UPSTREAM_MODIFY        0x0040
 #define NGX_HTTP_UPSTREAM_MAX_CONNS     0x0100
 
 
@@ -133,6 +138,8 @@ struct ngx_http_upstream_srv_conf_s {
 
 #if (NGX_HTTP_UPSTREAM_ZONE)
     ngx_shm_zone_t                  *shm_zone;
+    ngx_resolver_t                  *resolver;
+    ngx_msec_t                       resolver_timeout;
 #endif
 };