This directive is made obsolete in version 1.1.8, an equivalent limit_conn_zone directive with a changed syntax should be used instead:
limit_conn_zone $variable zone=name:size;
limit_conn_zone的描述:
When several limit_conn directives are specified, any configured limit will apply. For example, the following configuration will limit the number of connections to the server per client IP and at the same time will limit the total number of connections to the virtual host: