feat: wait for RADIUS host DNS resolution before startup (dns variant)

[jozefrebjak]

Problem

In Docker Swarm environments using the -dns image variant, the RADIUS server container may not be fully started when the Duo Auth Proxy starts. If RADIUS_HOST is a hostname (e.g. freeradius_primary), DNS resolution fails and the proxy exits immediately.

Only relevant for the -dns image variant where RADIUS_HOST can be a hostname.

Solution

Add wait_for_radius_hosts() in 01-init.sh that retries DNS resolution before startup.

Two new optional env variables:

• RADIUS_HOST_WAIT_RETRIES — max attempts (default: 30)
• RADIUS_HOST_WAIT_INTERVAL — seconds between attempts (default: 2)

With defaults, proxy waits up to 60 seconds for RADIUS host to become resolvable.