Apache VirtualHost conditional based on an environment variable - apache

Question

I'm trying to include a config file inside an Apache 2.4 <VirtualHost> based on the presence of an environment variable.
Inside the VirtualHost declaration, I set the VIEWMODE environment variable as such:
Define virtualhost_config "${virtualhost_path}/conf/virtualhost.conf"
<VirtualHost *:80>
SetEnv VIEWMODE demo
Include "${virtualhost_config}"
</VirtualHost>
Inside the included config file, I now have this conditional inside the <Directory> block:
<If "env('VIEWMODE') == 'demo'">
RewriteRule (.*) http://www.apple.com/ [L,R=302]
</If>
However, I can't seem to get this to work. The conditional RewriteRule is ignored.
What am I missing?

Answer 1

See the documentation for SetEnv:
The internal environment variables set by this directive are set after most early request processing directives are run, such as access control and URI-to-filename mapping. If the environment variable you're setting is meant as input into this early phase of processing such as the RewriteRule directive, you should instead set the environment variable with SetEnvIf.
And the note about environment variables within the functions section of the Apache Expresions documentation is also of interest:
Environment variable ordering
When environment variables are looked up within an <If> condition, it's important to consider how extremely early in request processing that this resolution occurs. As a guideline, any directive defined outside of virtual host context (directory, location, htaccess) is not likely to have yet had a chance to execute. SetEnvIf in virtual host scope is one directive that runs prior to this resolution
When reqenv is used outside of <If>, the resolution will generally occur later, but the exact timing depends on the directive the expression has been used within.
So you need to use SetEnvIf because SetEnv is not processed soon enough, and that fixed it for me when I tested here. Something like:
Define virtualhost_config "${virtualhost_path}/conf/virtualhost.conf"
<VirtualHost *:80>
SetEnvIf Request_URI ^ VIEWMODE=demo
Include "${virtualhost_config}"
</VirtualHost>

Answer 2

I solved this by setting an Apache variable, which then fed both the SetEnv directive as well as the <If> block. Unfortunately, the <If> block itself seemed to cause issues with the processing order of directives inside it (e.g. ServerAlias not allowed here), but <IfDefine> did not have this problem (using <IfDefine> only worked for me because VIEWMODE was binary). The final solution looked something like this:
Define environment production
Define viewmode demo
<VirtualHost *:80>
SetEnv ENVIRONMENT ${environment}
<IfDefine viewmode>
SetEnv VIEWMODE ${viewmode}
Include "${virtualhost_path}/conf/demo-configuration.conf"
</IfDefine>
</VirtualHost>
UnDefine environment
UnDefine viewmode
An important caveat is that Apache variables are global, so if the same variables might be used in subsequent Virtual Hosts, make sure to UnDefine them at the end of each config.