Difference between ServerName and ServerAlias

Question

I'm not quite clear on the difference between ServerName and ServerAlias. It looks like both of them work as host name settings, except that ServerAlias only works within the <VirtualHost> tag.

That is, I can do:

ServerName www.domain1.com
ServerName www.domain2.com

or:

<VirtualHost *:80>
ServerName www.domain1.com
ServerName www.domain2.com
</VirtualHost>

and both domains work on the same box. Can I use either ServerName or ServerAlias in this case?

score 41 · Accepted Answer · edited Jul 02 '13 at 19:23

41

The ServerName directive is

Hostname and port that the server uses to identify itself

Whilst ServerAlias is

Alternate names for a host used when matching requests to name-virtual hosts

Given a vhost configured like

 ...
 ServerName example.com
 ServerAlias www.example.com foo.example.com *.somewherelse.org
 ...

apache would respond to example.com, www.example.com foo.example.com and anything in .somewherelse.org with this VirtualHost

edited Jul 02 '13 at 19:23

voretaq7

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answered Aug 15 '12 at 14:50

user9517

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I totally understand. What I mean is that the hostnames seem to work whether I specify them as ServerName or ServerAlias. So is the difference between these two directives just semantic then - and they do the same thing? – Suman Aug 15 '12 at 14:56
1

@Suman: ServerName can be used to determine other information as required. Take a look at [UseCannonicalName](http://httpd.apache.org/docs/current/mod/core.html#usecanonicalname) for example. Also if run apacectl -S | httpd -S ... etc only the last defined ServerName for each vhost is printed, so you should really only have one ServerName. – user9517 Aug 15 '12 at 16:03
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If I understand correctly, `ServerName` does everything that `ServerAlias` does, and a bit more. But there should be only one `ServerName`. – Stefan Lasiewski Dec 11 '12 at 00:26

Dazed · Answer 2 · 2013-03-08T17:13:58.877

One Key difference that I have found by experiment (based on necessity) is that when used with wildcard sub-domains (e.g. "*.mycompany.com" and "*.mycompany.net") then the wildcard must be specified as ServerAlias and not ServerName.

I haven't tried this with non-SSL but with SSL this was the case (for me). I settled on a configuration of:

Listen *:8443    
NameVirtualHost *:8443
SSLStrictSNIVHostCheck off

<VirtualHost *:8443>
    ServerName mycompany.com
    ServerAlias *.mycompany.com
    ...
</VirtualHost>

<VirtualHost *:8443>
    ServerName mycompany.net
    ServerAlias *.mycompany.net
    ...
</VirtualHost>

When using "ServerName *.mycompany.net" then the first Virtual Host was always used. This wasn't just the certificate it was rewriting and proxying logic as well.

It is entirely possible that this only happens with SSL as there are a whole heap of other things going - as referenced in SSL with Virtual Hosts Using SNI and many ServerFault threads. Having followed all the advice in these this was the last head scratching aspect.

I came to this thread to try and understand myself why there was a difference and confess I get closer but not quite full understanding.

In my case ServerName seems to do a little less (isn't picked up in virtual host search), rather than more.

Running "apacectl -S | httpd -S" as per Iain's advice gives:

wildcard NameVirtualHosts and _default_ servers:
*:8443                 is a NameVirtualHost
         default server mycompany.com (/etc/httpd/conf/httpd.conf:1100)
         port 8443 namevhost mycompany.com (/etc/httpd/conf/httpd.conf:1100)
                 wild alias *.mycompany.com
         port 8443 namevhost mycompany.net (/etc/httpd/conf/httpd.conf:1164)
                 wild alias *.mycompany.net

Edit: (adding ServerName with the wildcard for completeness)

wildcard NameVirtualHosts and _default_ servers:
*:8443                 is a NameVirtualHost
         default server *.mycompany.com (/etc/httpd/conf/httpd.conf:1040)
         port 8443 namevhost *.mycompany.com (/etc/httpd/conf/httpd.conf:1040)
         port 8443 namevhost *.mycompany.net (/etc/httpd/conf/httpd.conf:1105)

Note: the word "wild" in the alias line, in the first case (using ServerAlias), comes from apache and it don't show in the second (using ServerName) - I suspect this is significant.

In addition, if I remove "ServerName" from second VirtualHost and just use an Alias following the advice "there should be only one ServerName" then a request gets a bit lost - seems to automatically redirect to "https://test.mycompany.net:8443" - as (in my case) 8443 isn't showing externally (nat'd) then it fails. Yes, I know for 443 this might work, but possibly shows something else is going on.

So, perhaps not an answer to the question, but a bit of documentation for someone else struggling with similar setup.

This really aught to be obvious that you can't have a wildcard in ***THE NAME*** of the server. Aliases specify alternate name(s), since that's possibly plural having wildcard matches makes sense. — Chris S, Jul 09 '13 at 13:47
Perhaps yes, but plenty of software/utilities allow and use a wild card in the "name" to mean *many* and don't specify it in the manual (e.g. see "[man cp](http://unixhelp.ed.ac.uk/CGI/man-cgi?cp)"). To support your point the apache documentation does say "*uniquely* identify a virtual host" (for ServerName) and "may include wildcards" (for ServerAlias). However, my point, Apache doesn't complain of an invalid config when wild card is specified in the ServerName (perhaps it should) and my purpose in posting here was to aid others seeking to use the wildcard virtual host approach. — Dazed, Nov 30 '13 at 13:22
@Dazed Thank you for this clear distinction. There is **nothing obvious** about 'ServerName'. If it were called 'CanonicalName', _that_ would be obvious. — DaveGauer, Mar 17 '17 at 17:41

score 5 · Answer 3 · edited Apr 13 '17 at 12:14

When dealing with software, it is often important to have one single point of truth. ServerName can be considered the "Real" canonical name of a host. ServerAlias is not.

ServerName does everything that ServerAlias does, and a bit more. As a best practice only set one ServerName, since there should only be one "Canonical" anything. If ServerName is not explicitly set, the httpd will determine a name on it's own.

ServerAlias on the other hand is just an alias, and can only be used in the VirtualHost context. There can be as many of these as you'd like.

If the site is served over HTTPS, then the ServerName should match one of the names contained the Certificate. If your certificate was created for www.example.org , but your configuration says:

ServerName foo.example.org
ServerAlias www.example.org

Then Apache will complain with the following error:

Dec 10 13:23:45 web1 httpd[1234]: [warn] RSA server certificate CommonName (CN) `www.example.org' does NOT match server name!?

score 1 · Answer 4 · answered Aug 15 '12 at 18:38

1

ServerName is the name apache will use when it has to use its own name in a URL in for example a redirect for a directory listing.

answered Aug 15 '12 at 18:38

Koos van den Hout

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Difference between ServerName and ServerAlias

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