Nginx configuration is bound to its workers. When you reload nginx new workers are created(and start responding to new connections) and the old ones are drained

Nginx configuration is bound to its workers. When you reload nginx new workers are created(and start responding to new connections) and the old ones are drained. The draining finishes when the last connection is finished or a timeout is reached. In OSS nginx every upstream change requires a configuration reload. If you have lots of upstream changes and don't want to terminate connections prematurely, this can quickly require lots of RAM as you have many workers. Stock nginx worker is around 150Mb, but issues with openresty integration(they mention lua usage) can bloat this to > 1GB.