Commit 2c48b1896 (1.45.2) made the internal nginx proxy listen on the IPv6
wildcard ('listen [::]:7575;'), which aborts nginx startup on hosts/VMs with
IPv6 disabled:
nginx: [emerg] socket() [::]:7575 failed (97: Address family not supported by protocol)
A plain revert would reintroduce #2697 and break IPv6-only/dual-stack
environments where this listener is required. Instead, only emit the IPv6
listen directive when the host actually has IPv6 configured.
Reuse the envsubst step run.sh already performs: compute NGINX_LISTEN_IPV6
from /proc/net/if_inet6 and substitute it into the template. proc files always
report size 0, so presence is detected by grepping the file (not 'test -s').
ajnart
cb53e2e548