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, 19 insertions, 0 deletions

diff --git a/src/stream/ngx_stream_proxy_module.c b/src/stream/ngx_stream_proxy_module.c
index bbf4f7ec0..0890a04ae 100644
--- a/src/stream/ngx_stream_proxy_module.c
+++ b/src/stream/ngx_stream_proxy_module.c
@@ -742,6 +742,25 @@ ngx_stream_proxy_connect(ngx_stream_session_t *s)
 
     u->state->peer = u->peer.name;
 
+#if (NGX_STREAM_UPSTREAM_ZONE)
+    if (u->upstream && u->upstream->shm_zone
+        && (u->upstream->flags & NGX_STREAM_UPSTREAM_MODIFY))
+    {
+        u->state->peer = ngx_palloc(s->connection->pool,
+                                    sizeof(ngx_str_t) + u->peer.name->len);
+        if (u->state->peer == NULL) {
+            ngx_stream_proxy_finalize(s, NGX_STREAM_INTERNAL_SERVER_ERROR);
+            return;
+        }
+
+        u->state->peer->len = u->peer.name->len;
+        u->state->peer->data = (u_char *) (u->state->peer + 1);
+        ngx_memcpy(u->state->peer->data, u->peer.name->data, u->peer.name->len);
+
+        u->peer.name = u->state->peer;
+    }
+#endif
+
     if (rc == NGX_BUSY) {
         ngx_log_error(NGX_LOG_ERR, c->log, 0, "no live upstreams");
         ngx_stream_proxy_finalize(s, NGX_STREAM_BAD_GATEWAY);