RISC-V support

[olof-nord]

Is your feature request related to a problem? Please describe

Using the nginx unprivileged docker image on a riscv64 system.

Describe the solution you'd like

Adjusting the CI to also build and publish linux/riscv64 images.

Ubuntu 20.04 supports RISC-V, QEMU/docker buildx also supports RISC-V.

The Ubuntu impish-updates,impish-security apt repositories also already includes a built nginx, 1.18.0-6ubuntu11.1 as of today, and as such I understand that the project should also compile under riscv64.

Describe alternatives you've considered

Well, the alternative is to not provide riscv64 support, which is the current situation.

Additional context

RISC-V is an open standard instruction set architecture, which is under rapid development. Distributions including AOSP, Arch Linux, Debian, Gentoo Linux, Fedora, OpenEuler, etc are also actively doing porting work for this architecture.

[olof-nord]

Re-reading the project setup I see that the base of the images are not Ubuntu, but Debian: the support there is an ongoing effort.
The most official riscv64 Debian docker images I know of are the ones found under riscv64/debian:
https://hub.docker.com/r/riscv64/debian

Edit: The Debian Docker linux/riscv64 support has made its way to the debian:sid/debian:unstable/debian:experimental tags, but not (yet) to the debian:bullseye image.

[alessfg]

Can you open this issue in the upstream NGINX Docker repo https://github.com/nginxinc/docker-nginx too? I see no reason not to support the platform once it makes it to the mainstream Debian image.