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Re: [users@httpd] <VirtualHost> matches when ServerName directive is omitted


On 06/23/2018 10:34 AM, billy noah wrote:
Thanks Eric, the rdns almost certainly /did /change so that could be the culprit.  Do you have a definitive answer or a way to determine how apache decides what "ServerName" should be when the directive is absent?

From the documentation:

    If no ServerName is specified, the server attempts to deduce the
    client visible hostname by first asking the operating system for the
    system hostname, and if that fails, performing a reverse lookup on
    an IP address present on the system.

so basically it will do a gethostname() call first, falling back to a reverse lookup.

With regards,
Daniel.

I'll stick with the policy of using something (even nonsense as
you suggested) in the future, but I'm curious to understand the precise mechanics of what is happening here.  Is there some way to get a log of apache's decision making factors when determining which vhost to serve?

On Sat, Jun 23, 2018 at 11:28 AM, Eric Covener <covener@xxxxxxxxx <mailto:covener@xxxxxxxxx>> wrote:

    On Sat, Jun 23, 2018 at 11:22 AM billy noah <billynoah@xxxxxxxxx
    <mailto:billynoah@xxxxxxxxx>> wrote:
    >
    > I am in the process of migrating some sites from a server running Apache 2.4.7 to a new installation (Ubuntu 18) running Apache 2.4.29 and running into some issues with VirtualHost matching.
    >
    > On my old server I have a config like this:
    >
    > <VirtualHost 12.34.56.78:80 <http://12.34.56.78:80>>
    >     ServerAlias *.dev.example.com <http://dev.example.com>
    >     VirtualDocumentRoot /var/www/dev/%1
    > </VirtualHost>
    >
    > <VirtualHost 12.34.56.78:80 <http://12.34.56.78:80>>
    >     ServerName example.com <http://example.com>
    >     ServerAlias www.example.com <http://www.example.com>
    >     DocumentRoot /var/www/example/
    > </VirtualHost>
    >
    > As you can see, the ServerName directive is intentionally absent from the first host which uses a VirtualDocumentRoot to serve directories based on the subdomain. This has been working fine on the old server.

    It's unwise. You should at least pick some nonsense name.

    >
    > In my new environment everything worked fine at first, but today (no updates, nothing changed), oddly things changed. For some reason apache started matching example.com <http://example.com> to the first vhost and after some
    amount of debugging I have determined that this is due to the lack
    of ServerName directive. When I add one - anything really - the
    problem goes away. So to be clear, a working config now looks like this:
    >
    > <VirtualHost 12.34.56.78:80 <http://12.34.56.78:80>>
    >     ServerName anything.dev.example.com <http://anything.dev.example.com>
    >     ServerAlias *.dev.example.com <http://dev.example.com>
    >     VirtualDocumentRoot /var/www/dev/%1
    > </VirtualHost>
    >
    > <VirtualHost 12.34.56.78:80 <http://12.34.56.78:80>>
    >     ServerName example.com <http://example.com>
    >     ServerAlias www.example.com <http://www.example.com>
    >     DocumentRoot /var/www/example/
    > </VirtualHost>

    Perhaps the reverse DNS of your IP address changed?  I don't think
    it's directly the "system hostname".

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