Thank you Matthew to take a little time review my issue.
Let me clarify one point : it’s not only Docker that is impacted by caddy configuration, but also apt-get and even a simple curl (download of DO-agent install.sh for installation). When I stop caddy, apt-get and curl works fine again.
It’s looks like https and certificates is messed up by caddy as suspected by
curl: (51) SSL: certificate subject name (api.fame.community) does not match target host name 'agent.digitalocean.com'