Hi, people. I figured out the problem in my load balancer.
Interestingly, when 'ProxyPass/assets balancer://static/' is set, Apache,
proxys the request on to the destination balancer member without the string
that indicates the request to proxy (in this case, '/assets'). So if the
request is 'http://domain.ca/assets/monalisa.jpg', the request passed on to the
balancer member is actually 'http://domain.ca/monalisa.jpg'. Of course, the
application server these requests were being sent to in my case does not have a
file called "monalisa.jpg" (or the actual file in question, which of course,
has a different name) at '/'. The file is at /assets/. So the application
server returned a 404, like any good web application server should.
The solution then, was to add the string, '/assets' to the end of the target
location in the ProxyPass directive.
So my ProxyPass directives look like this now:
> ProxyPass/assets balancer://static/assets
> ProxyPassReverse/assets balancer://static/assets
>
> ProxyPass / balancer://dynamic/
> ProxyPassReverse / balancer://dynamic/
Note the difference between the two conditions defined.
* The top ProxyPass directives send all requests starting with the string,
'/assets' to 'balancer://static/assets', to the static asset cache (in my
case), ensuring that the original URI of the request remains the same.
* The second set of ProxyPass and ProxyPassReverse directives send everything
else to the other balancer.
Once I added that '/assets' bit to the end of those first ProxyPass directives,
the requests for '/assets' all worked. No more 404s!
I've checked the responses coming from Apache and do see that those for
'/assets' are sent on to the static asset cache as well -- the responses for
them come back with Varnish headers.
So, hopefully this information is helpful to anyone else who wants to split
requests from an Apache load balancer to two different load balance pools. I
searched high and low and did not see any information about how to do this
anywhere (though someone might have information posted about it somewhere). I
will probably write a blog post about it myself as well. :)
Best,
Michela
‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Sunday, August 8th, 2021 at 5:15 PM, Michela <mich...@protonmail.com> wrote:
> Hello, everyone!
>
> I am using Apache as a load balancer, and have an issue with requests
> returning a 404 status code, unless they match a ProxyPass directive with a
> source value of "/". Can you help me identify the reason for this?
>
> My load balancer configuration bits (just let me know if I should also send
> in the rest):
>
>> RequestHeaderset X-Forwarded-Proto https
>>
>> SSLProxyEngineOn
>> SSLProxyVerifyNone
>> SSLProxyCheckPeerCN Off
>> SSLProxyCheckPeerName Off
>> SSLProxyCheckPeerExpire Off
>>
>> # IMPORTANT: Never remove ProxyRequests, and never set it to 'on'!
>> ProxyPreserveHostOn
>> ProxyRequestsoff
>> ProxyViaOff
>>
>> # Load balancer configuration
>> ProxyHCExpr ok234 {%{REQUEST_STATUS} =~ /^[234]/}
>> ProxyHCExpr gdown {%{REQUEST_STATUS} =~ /^[5]/}
>>
>> <Proxy balancer://static>
>> BalancerMember http://127.0.0.1:8080
>> ProxySet lbmethod=byrequests
>> </Proxy>
>>
>> <Proxy balancer://dynamic>
>> BalancerMember http://127.0.0.1:8080
>> ProxySet lbmethod=byrequests
>> </Proxy>
>>
>> ProxyPass/assets balancer://static/
>> ProxyPassReverse/assets balancer://static/
>>
>> ProxyPass / balancer://dynamic/
>> ProxyPassReverse / balancer://dynamic/
>
> I've set the BalancerMember value for the "static" balancer to the same as
> the "dynamic" balancer not just for testing -- to eliminate my static asset
> cache server (Varnish) as a potential cause of this problem.
>
> Another Apache virtual host is listening on 8080, which points to a Rails
> application running on Puma, served via a Unix socket. This is a staging
> server, the application servers in production will be on separate machines
> from the load balancers.
>
> Any requests to this load balancer that start with '/assets' return 404 not
> found. If I comment out the ProxyPass and ProxyPassReverse lines for the
> '/assets' URI, meaning all requests go to the same balancer ("dynamic"), then
> everything works great -- no 404s.
>
> I have carefully reviewed the documentation at
> http://httpd.apache.org/docs/current/mod/mod_proxy_balancer.html several
> times, checked Apache's logs with debug verbosity, searched countless forums,
> mailing lists, blog posts, and the web in general for any indication of what
> I might have wrong here, and I still can't find the issue. That's strange to
> me, because I have seen several configuration examples online, where traffic
> from something other than "/" is sent to a given balancer member via
> ProxyPass, and I can't see anything significantly different between those
> (presumably properly working) configurations and my own. :|
>
> More information on my set-up:
> Apache 2.4.37-39.0.1
> OS: Enterprise Linux 8.4 (RHEL / Oracle / CentOS, etc)
> Application: Custom Ruby on Rails application, running in Ruby 2.7, Rails
> 3.2, and Puma 5.4.0.
> System is a virtual machine with two vCPUs and 4 GB RAM.
>
> If I've missed any key information in my query, or if it would be helpful to
> have more information about the environment or problem, please tell me. :)
>
> Thank you for any help you may be able to provide!!
>
> Best,
> Michela
