stunnel is a TLS/SSL proxy for programs that themselves serve only via HTTP, such as Fossil. (Fossil can speak HTTPS, but only as a client.) stunnel decodes the HTTPS data from the outside world as HTTP before passing it to Fossil, and it encodes the HTTP replies from Fossil as HTTPS before sending them to the remote host that made the request.

You can run stunnel in one of two modes: socket listener — much like in our inetd doc — and as an HTTP reverse proxy. We’ll cover both cases here, separately.

Socket Activation

The following stunnel.conf configuration configures it to run Fossil in socket listener mode, launching Fossil only when an HTTPS hit comes in, then shutting it back down as soon as the transaction is complete:

    [fossil]
    accept       = 443
    TIMEOUTclose = 0
    exec         = /usr/bin/fossil
    execargs     = /usr/bin/fossil http /home/fossil/ubercool.fossil --https
    cert         = /etc/letsencrypt/live/ubercool-project.org/fullchain.pem
    key          = /etc/letsencrypt/live/ubercool-project.org/privkey.pem
    ciphers      = ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-RSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:AES256-GCM-SHA384:AES128-GCM-SHA256:AES256-SHA256:AES128-SHA256:AES128-SHA:DES-CBC3-SHA
    options      = CIPHER_SERVER_PREFERENCE

This configuration shows the TLS certificate generated by the Let’s Encrypt Certbot in certonly mode. There are other ways to get TLS certificates, but this is a popular and free option.

You will need to adjust the site names and paths in this example. Where this file goes varies by OS type, so check the man pages on your system to find out where it should be locally.

See the stunnel documentation for further details about this configuration file.

It is important that the fossil http command in that configuration include the --https option to let Fossil know to use “https://” instead of “http://” in generated hyperlinks.

Reverse Proxy

You can instead have Fossil running in the background in standalone HTTP server mode, bound to a high random TCP port number on localhost via the --localhost and --port flags, then configure stunnel to reverse proxy public HTTPS connections down to it via HTTP.

The configuration is the same as the above except that you drop the exec and execargs directives and add this instead:

    connect      = 9000

That tells stunnel to connect to an already-running process listening on the given TCP port number.

There are a few advantages to this mode:

1. At the cost of some server memory and a tiny bit of idle CPU time, Fossil remains running so that hits can be served a smidge faster than in socket listener mode, where the Fossil binary has to be loaded and re-initialized on each HTTPS hit.

2. The socket listener mode doesn’t work on all platforms that stunnel runs on, particularly on Windows.

Return to the top-level Fossil server article.