backend server hostnames are resolved lazily

src/nc_conf.c

@@ -1635,10 +1635,13 @@ conf_add_server(struct conf *cf, struct command *cmd, void *conf)
         return CONF_ERROR;
     }
 
-    status = nc_resolve(&field->addrstr, field->port, &field->info);
-    if (status != NC_OK) {
-        return CONF_ERROR;
-    }
+    /*
+     * The address resolution of the backend server hostname is lazy.
+     * The resolution occurs when a new connection to the server is
+     * created, which could either be the first time or every time
+     * or every time the server gets re-added to the pool after an
+     * auto ejection.
+     */
 
     field->valid = 1;
 

src/nc_server.c

@@ -22,6 +22,23 @@
 #include <nc_server.h>
 #include <nc_conf.h>
 
+static void
+server_resolve(struct server *server, struct conn *conn)
+{
+    rstatus_t status;
+
+    status = nc_resolve(&server->addrstr, server->port, &server->info);
+    if (status != NC_OK) {
+        conn->err = EHOSTDOWN;
+        conn->done = 1;
+        return;
+    }
+
+    conn->family = server->info.family;
+    conn->addrlen = server->info.addrlen;
+    conn->addr = (struct sockaddr *)&server->info.addr;
+}
+
 void
 server_ref(struct conn *conn, void *owner)
 {
@@ -30,9 +47,7 @@ server_ref(struct conn *conn, void *owner)
     ASSERT(!conn->client && !conn->proxy);
     ASSERT(conn->owner == NULL);
 
-    conn->family = server->info.family;
-    conn->addrlen = server->info.addrlen;
-    conn->addr = (struct sockaddr *)&server->info.addr;
+    server_resolve(server, conn);
 
     server->ns_conn_q++;
     TAILQ_INSERT_TAIL(&server->s_conn_q, conn, conn_tqe);
@@ -454,6 +469,12 @@ server_connect(struct context *ctx, struct server *server, struct conn *conn)
 
     ASSERT(!conn->client && !conn->proxy);
 
+    if (conn->err) {
+      ASSERT(conn->done && conn->sd < 0);
+      errno = conn->err;
+      return NC_ERROR;
+    }
+
     if (conn->sd > 0) {
         /* already connected on server connection */
         return NC_OK;