Use ENTRYPOINT + CMD for easier configurability

Now there is CMD ["/usr/local/openresty/bin/openresty", "-g", "daemon off;"], but it could be

ENTRYPOINT ["/usr/local/openresty/bin/openresty"]
CMD ["-g", "daemon off;"]

And if I want to override the -g argument, I could do just

docker run openresty/openresty:alpine -g "daemon off; env MY_ENV_FOR_LUA;"

Without having to be concerned where the openresty binary resides.

How to verify functionality

Dockerfile

FROM openresty/openresty:alpine

ENTRYPOINT ["/usr/local/openresty/bin/openresty"]
CMD ["-g", "daemon off;"]

Build it

docker build -t test .

Run it

docker run --rm -it -e FOO=bar test -g 'daemon off; env FOO;'

Exec into and see process with top

    {openresty} nginx: master process /usr/local/openresty/bin/openresty -g daemon off; env FOO;

Start by locating the repository Dockerfile that currently defines CMD, then compare its image configuration with the ENTRYPOINT and CMD shown in the issue. Build the image and run the provided docker commands to verify that overriding the -g argument works and that the OpenResty process starts with the supplied environment expression.