> Ports below 1024 can be opened only by root.

Or processes running with the CAP_NET_BIND_SERVICE capability! [1]

Capabilities are a Linux kernel feature. Granting CAP_NET_BIND_SERVICE to nginx means you do not need to start it with full root privileges. This capability gives it the ability to open ports below 1024

Using systemd, you can use this feature like this:

    [Service]
    ExecStart=/usr/bin/nginx -c /etc/my_nginx.conf
    AmbientCapabilities=CAP_NET_BIND_SERVICE
    CapabilityBoundingSet=CAP_NET_BIND_SERVICE
    User=nginx
    Group=nginx

(You probably also want to enable a ton of other sandboxing options, see `systemd-analyze security` for tips)

[1]: https://man7.org/linux/man-pages/man7/capabilities.7.html

Nginx is started as root but it does not run as root, it changes its user after opening log files and sockets. (unless you use a lazy docker container and just run everything as root inside it).

Even in (the official) docker image, a nginx user is created: (latest, layer 6)

/bin/sh -c set -x && groupadd --system --gid 101 nginx && useradd --system --gid nginx --no-create-home --home /nonexistent --comment "nginx user" --shell /bin/false --uid 101 nginx .....

[1] https://hub.docker.com/layers/library/nginx/latest/images/sh...

Nginx workers shouldn’t run as root and certainly don’t on any distro I know. Typically you have a www-data user/group or equivalent. Dropping privilege is very basic.