How do I respond on ssl error when using on demand tls?

[altlimit]

1. Output of caddy version:

v2.6.1 h1:EDqo59TyYWhXQnfde93Mmv4FJfYe00dO60zMiEt+pzo=

2. How I run Caddy:

sudo systemctl restart caddy.service

a. System environment:

debian 11

d. My complete Caddy config:

{
        on_demand_tls {
                ask https://example.com/check
                interval 2m
                burst 5
        }
}

:80, :443 {
        reverse_proxy https://example.com {
                header_up Host {upstream_hostport}
        }
        tls {
                on_demand
        }
        handle_errors {
                respond "404 Not Found"
        }
}

3. The problem I’m having:

When my ask fail for on_deman_tls I expect to see “404 Not Found” respond for handle_errors. I see ERR_SSL_PROTOCOL_ERROR from chrome.

[matt (Matt Holt)]

HTTP responses can only be sent after a connection is established, so if no connection can be established, an HTTP response is impossible. (This is not unique to Caddy. That’s just how the Web works.)