Domtool SSL vhosts… Oh the Joy

Once upon a time, basically no one used SSL at HCoop, because you needed a dedicated IP and it was generally a pain. So we never really got any decent documentation (it manages to just not explain things like what kind of certificate we need). And it seems that the way SSL is implemented in Domtool is kind of a hack. Now that TLS SNI works out of the box, I suspect members might want to actually use SSL.

To create an SSL vhost today:

dom "foo.bar" with
  web "baz" where
    SSL = use_cert "/etc/apache2/ssl/user/myfancycert.pem";
  with
    serverAliasDefault;
  end;
end;

Setting the SSL environment variable causes Domtool to turn on the SSLEngine, change the ports, etc. This works for the simple case of a self-signed cert or one signed by a root certificate commonly distributed. Unfortunately, at least Gandi uses intermediate certificates that aren’t universally distributed to sign certificates (sensible), but those are signed by well known trusted root certificates. So: SSLCertificateChainFile must be supported.

Adding a new cacert permission and the trivial types and action needed to support it is easy, but there’s a problem: you can’t use the directive with the SSL engine off, and there’s no way to use the type checker to enforce this. My immediate workaround is just ignoring the directive during the eval phase when we’re not in an SSL vhost, but this isn’t clean. Of course, the kerberos authentication type also behaves this way, and the Domtool type system only promises to avoid creating maliciously invalid configuration.

It seems like contexts were designed just for this, and so the logical thing to do seems to be creating a new sslHost container of some sort that either goes inside or outside of vhost. Then, that container would declare an SSL context and the typing for any ssl dependent commands would do the right thing. But: which way is best? I’m not a type theorist, making this probably easy problem frustrating. Outside:

sslHosts with
    web "baz" where
      SSL = use_cert "/etc/apache2/ssl/user/myfancycert.pem";
    with
      serverAliasDefault;
    end;
  end;

My first thoughts were that this was the best way, but the only advantage seems being able to define a number of SSL vhosts at once (but we have abstraction in Domtool, negating that benefit). The disadvantages include continuing to allow users to shoot themselves in the foot by doing things like defining the SSL and non-SSL vhost for the same domain on different machines (probably a sign that the current and this approach are both Wrong™).

So, then, inside:

dom "foo.bar" with
  web "baz" where
    DocumentRoot = home "whatever";
  with
    serverAliasDefault;
    sslHost where
      SSL = use_cert "foo.pem";
    with
      serverAliasDefault;
    end;
  end;
end;

I think this is the Right Way ™ now. It prevents users from accidentally creating unreachable hosts and mandates that the SSL host configuration be kept with the other vhost configuration. At first glance, it might look hard to use (you’d have to duplicate the non-ssl and ssl vhost actions in both to make them identical), but yet again abstraction comes to the rescue and it would be trivial to define a function to duplicate the vhost body. Much of the time, the non-ssl host only exists to redirect to the ssl host as well, so this version would save some typing (at the keyboard) in the case.

The only thing that strikes me as possibly wrong is that the ssl vhost is under the vhost, when ssl-ness is more of an attribute of the vhost. Maybe the hierarchy doesn’t matter… I just fear that I would be abusing the context/predicate system. Perhaps instead there should be vhostSSL types (with easy domain webSSL/webSSLAt abstractions). This is what happens when a Lisp hacker inherits code from a type theory wizard.

Another possibility: actions can require that environment variables have certain types when they are invoked, and domtool uses predicates on base types to determine a refined type. Vhosts require that SSL be of type ssl which includes the value no_ssl; if you could refine an already refined type (you can’t, and there’s probably a good reason), a sane strategy might be to do that instead on any actions dependent upon SSL being enabled. Of course, that still doesn’t solve the problem of allowing users to create unreachable vhosts if they accidentally define the ssl and non-ssl vhosts on different nodes. Perhaps that has a different solution, or isn’t worth solving.

Domtool SSL vhosts… Oh the Joy by clinton is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License.