NGINX, logging in Logstash JSON

nginx-logstash.conf

    log_format logstash_json '{ "@timestamp": "$time_iso8601", '
                             '"@version": 1, '
                             '"message": "$request $status $body_bytes_sent", '
                             '"remote_addr": "$remote_addr", '
                             '"remote_user": "$remote_user", '
                             '"body_bytes_sent": "$body_bytes_sent", '
                             '"request_time": "$request_time", '
                             '"status": "$status", '
                             '"request": "$request", '
                             '"request_method": "$request_method", '
                             '"server_protocol": "$server_protocol", '
                             '"http_referrer": "$http_referer", '
                             '"user_agent": "$http_user_agent" }';

    access_log  /var/log/nginx/access.log  logstash_json;