TLS ALPN without downtime

Using TLS-ALPN without downtime

acme.sh added support for TLS-ALPN on 2018-12-28.

This feature allows domain validation to be performed over port 443, useful when port 80 is not accessible. However, the feature requires any existing webservers on that port to be shut down so that acme.sh can listen on port 443.

This article outlines some ways it is possible to configure webservers to work transparently with acme.sh's TLS-ALPN support without having to stop and start your webserver.

Compatibility

Webserver	Status	Caveats
Apache httpd	Not yet possible	-
nginx	Supported	Requires ngx_stream_ssl_preread_module to be compiled. e.g. on Ubuntu 18.04, included in the nginx-full package.
haproxy	Not yet possible	-

Instructions

nginx

With nginx, what we do is create a TLS-ALPN load balancer within nginx on port 443, and re-assign all existing HTTPS virtual hosts within nginx to another port.

When a TLS-ALPN connection comes in, it is routed to acme.sh, otherwise, the connection is routed to the HTTPS virtual hosts.

1. Verify that nginx is compiled with the required module:

$ nginx -V 2>&1 | grep -o ssl_preread
ssl_preread

2. Re-assign ALL port 443 virtual hosts to another port

If you have existing HTTPS virtual hosts listening on port 443, you will need to re-assign each HTTPS server to an alternate port (such as 8443), so that we can put the ALPN load balancer on port 443.

For example

server {
    server_name example.org;
    listen 443;
    # ...
}

would become

server {
    server_name example.org;
    listen 8443;
    # ...
}

3. Add the ALPN load balancer

In /etc/nginx.conf, at the end of the file, add (substituting 8443 for the port chosen in step 2):

stream {
  map $ssl_preread_alpn_protocols $tls_port {
    ~\bacme-tls/1\b 10443;
    default 8443;
  }
  server {
    listen 443;
    listen [::]:443;
    proxy_pass 127.0.0.1:$tls_port;
    ssl_preread on;
  }
}

4. Make sure the configuration works and reload.

$ sudo nginx -t
$ sudo systemctl reload nginx

5. Try to issue a certificate (substituting example.org for the domain you want on your certificate).

$ sudo acme.sh --issue --alpn --tlsport 10443 -d example.org