Howto serve a second subdomain through Apache Proxy - apache

Question

I have an Apache frontend server, that until today proxies traffic for a subdomain api.myapp.net to a backend server running a Rails app on an Nginx.
Now I added a second subdomain alpha.myapp.net in my domain portfolio and gave it the same IP. Traffic to that subdomain shall not hit the Rails application, but a second VHost on the Nginx server that is setup to serve a static site.
So I have a proxy config for api.myapp.net:
NameVirtualHost *:80
<VirtualHost *:80>
ServerAdmin webmaster#myapp.net
ServerName api.myapp.net
ServerAlias api.myapp.net
DirectoryIndex index.html
RewriteEngine On
RewriteLog /var/log/apache2/rewrite.log
RewriteLogLevel 9
RewriteCond %{HTTP_HOST} !^(api\.)?myapp\.net$
RewriteRule ^(.*)$ http://myapp.net$1 [L,R=301]
ProxyPass / http://192.168.1.145/
ProxyPassReverse / http://192.168.1.145/
ErrorLog /var/log/apache2/error.log
LogLevel warn
CustomLog /var/log/apache2/access.log combined
ServerSignature Off
</VirtualHost>
And I setup a second config for alpha.myapp.net:
NameVirtualHost *:80
<VirtualHost *:80>
ServerAdmin webmaster#myapp.net
ServerName alpha.myapp.net
ServerAlias alpha.myapp.net
DirectoryIndex index.html
RewriteEngine On
RewriteLog /var/log/apache2/rewrite.log
RewriteLogLevel 9
RewriteCond %{HTTP_HOST} !^(alpha\.)?myapp\.net$
RewriteRule ^(.*)$ http://myapp.net$1 [L,R=301]
ProxyPass / http://192.168.1.145/
ProxyPassReverse / http://192.168.1.145/
ErrorLog /var/log/apache2/error.log
LogLevel warn
CustomLog /var/log/apache2/access.log combined
ServerSignature Off
</VirtualHost>
What happens now, is, that all traffic to alpha.myapp.net hits my Rails application that listens for requests for api.myapp.net.
I sorted out all Nginx config problems, so I thought it must be an Apache misconfiguration. What I see in Apache's rewrite log seems to explain the problem:
xxx.yyy.zzz.95 - - [08/Apr/2013:09:34:35 +0200] [alpha.myapp.net/sid#b9279870][rid#b9311d38/initial] (2) init rewrite engine with requested uri /index.html
xxx.yyy.zzz.95 - - [08/Apr/2013:09:34:35 +0200] [alpha.myapp.net/sid#b9279870][rid#b9311d38/initial] (3) applying pattern '^(.*)$' to uri '/index.html'
xxx.yyy.zzz.95 - - [08/Apr/2013:09:34:35 +0200] [alpha.myapp.net/sid#b9279870][rid#b9311d38/initial] (4) RewriteCond: input='alpha.myapp.net' pattern='!^(alpha\.)?myapp\.net$' => not-matched
xxx.yyy.zzz.95 - - [08/Apr/2013:09:34:35 +0200] [alpha.myapp.net/sid#b9279870][rid#b9311d38/initial] (1) pass through /index.html
The last part pass through /index.html seems to omit the subdomain and domain part. So the Nginx backend server does not now, which subdomain is requested, ans serves the request from the first available server, which ist api.
The question now seems to be: How can I proxy the traffic from Apache frontend to Nginx backend and maintain the subdomain and domain?
Or could there be another problem?
Hope someone can help.
Regards Felix

Answer 1

Sometimes the answer comes along with the question. The problem was exactly the missing hostname.
I solved the problem by editing /etc/hosts on my Apache server and adding two entries. One api.myapp.net, one alpha.myapp.net both referencing the same IP.
Then I changed bot Apache proxy configurations, so that ProxyPass and ProxyPassReverse do not use IP's anymore but the new hostnames.
And voila it works.