We're using Caddy in production. It's working quite well so far. It's a really smart helpful project.
I'd recommend reading the documentation. We had a nasty surprise when Caddy decided all our backend servers were broken and it removed them. After that we stopped naively running the proxy with the default settings. https://caddyserver.com/docs/proxy
We changed the default proxy failover behavior in 0.9.3. You now have to opt-in to failure handling by specifying the behavior you want. See https://github.com/mholt/caddy/pull/1135 for more details.
I'd recommend reading the documentation. We had a nasty surprise when Caddy decided all our backend servers were broken and it removed them. After that we stopped naively running the proxy with the default settings. https://caddyserver.com/docs/proxy