if no resolver is specified, what is the default DNS resolution behavior

[WKCLT]

I'd like to ask, when using openresty http request_uri, if no resolver is specified, what is the default DNS resolution behavior? My Nginx service is running inside Docker, and I added a host entry in the Docker container's /etc/hosts file. However, the domain name fails to resolve during the http.lua connect call. So I want to know: is the default domain name resolution behavior only using /etc/resolv.conf and not using /etc/hosts?