NGX_HTTP_UPSTREAM_BACKUP  309 src/http/modules/ngx_http_upstream_least_conn_module.c                   |NGX_HTTP_UPSTREAM_BACKUP;
NGX_HTTP_UPSTREAM_BACKUP 5279 src/http/ngx_http_upstream.c                                          |NGX_HTTP_UPSTREAM_BACKUP);
NGX_HTTP_UPSTREAM_BACKUP 5446 src/http/ngx_http_upstream.c             if (!(uscf->flags & NGX_HTTP_UPSTREAM_BACKUP)) {