"No protocol handler valid for the URL" with httpd mod_proxy_balancer

Question

I'm trying to set up failover for a reverse-proxied server with a localhost static copy of resources that would usually be served by a content management system. I've used wget to grab a static copy of the dynamic site for failover purposes.

I've tried to use a configuration similar to Fall-back location for Apache's ProxyPass directive? to get things started, and it's a fairly straightforward, but I'm getting the error in the title.

Here's my (sanitized) proxy configuration:

DocumentRoot /var/www/www.example.com/htdocs

ProxyRequests Off
ProxyPreserveHost On

ProxyPass "/site/" "balancer://cms"
ProxyPassReverse "/site/" "balancer://cms"
ProxyPassReverse "/site/" "http://ip-10-1-1-229.ec2.internal/site/"

<Proxy "balancer://cms">
    #BalancerMember "http://ip-10-1-1-229.ec2.internal/site/" loadfactor=1
    # For localhost services, a backup of the CMS's site
    BalancerMember "http://127.0.0.1/site-backup/www.example.com/site/" loadfactor=10 status=+H
</Proxy>

<Directory "/var/www/www.example.com/htdocs/site-backup">
  Order allow,deny
  Allow from all

  Options Indexes FollowSymlinks
  DirectoryIndex index.html
</Directory>

(Here, I've commented-out the balancer member that goes to the real CMS system -- that part is working just fine -- so that I can test the local, static copy.)

There is an index.html file in /var/www/www.example.com/site-backup/www.example.com/ and it does get loaded when I try to hit http://www.example.com/site/, but none of the page's other resources (CSS, images, etc.) get loaded. They have URLs in the page like:

I have a file, foo.png at this location:

/var/www/www.example.com/htdocs/site-backup/www.example.com/site/sites/default/files/foo.png

But when that image is loaded by the browser, I get a 500 Internal Server Error response and I see this in httpd's error log:

[proxy:warn] [pid 3182:tid 2838395712] [client 71.127.40.115:38208] AH01144: No protocol handler was valid for the URL /site/site/sites/default/files/foo.png. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule., referer: http://test.example.com/site/

I noticed that the URL shown in the error message has an extra /site/ in the URL, so I figured it was getting doubled because I'm trying to serve a URL space including /site/ from a directory containing /site/ and wget is probably not perfect right now, so I created a symlink from /var/www/www.example.com/site-backups/www.example.com/site/site/sites -> /var/www.www.example.com/site-backups/www.example.com/site/sites. That ought to have fixed any foolishness due to URL confusion.

But that didn't seem to fix anything; mod_proxy is still complaining about the protocol. mod_proxy_http is definitely enabled, as the normal ProxyPass directive to the CMS is working as expected (when enabled).

I'm sure this is a fairly simple thing I'm missing, but I can't seem to figure it out. Any help would be greatly appreciated.

Solution 1

facepalm

It turns out that I was missing a trailing slash on my ProxyPass directive:

ProxyPass "/site/" "balancer://cms"

should have been:

ProxyPass "/site/" "balancer://cms/"

(Note the trailing slash before the close-quote.)

That literally fixed everything.

I'm happy to delete this question and answer if folks want to close it as "simple typographical error", but I'll leave it for now. If I get some up votes on this answer, I'll remove this note and consider it a public service for anyone who might make the same mistake.

Solution 2

In my case, I needed proxy_ajp module.

a2enmod proxy proxy_http proxy_ajp 

Solution 3

Same as kujiy i had to add the mod_ajp.

I am using apache4.

My log showed messages as follows:

No protocol handler was valid for the URL /jira. 
If you are using a DSO version of mod_proxy, 
make sure the proxy submodules are included in 
the configuration using LoadModule 

so I added ( I mean uncommented) the following line to my httpd.conf:

LoadModule proxy_ajp_module modules/mod_proxy_ajp.so 

saved, and the restarted the apache server.

Comments

[Yogesh Devi]

A comment to kujiy's reponse could have sufficed , or an upvote... but alas my reputation ( or lack of it ... does not allow me to do that --- so thanks @kujiy

[Geremia]

why would a trailing slash matter?

[Christopher Schultz]

@Geremia The trailing slash is necessary on the origin-URL because the proxied URL has a trailing slash.

[Christopher Schultz]

Enabling mod_proxy_ajp is not useful for this particular application. You are answering a question which was not asked here.

[kujiy]

Yes, I know my answer was not just exactly for this question. Though sometimes we have to come to these similar questions when we google with the same error message. I don't know stackoverflow allows it or not but I believe it helps some people and me. Sorry. @ChristopherSchultz

[kujiy]

Your welcome @YogeshDevi. This is a problem about google and stackoverflow. If I and Devi make a new question and answer for proxy_ajp, it won't hit on google and this question will hit for the error message.

[RTK]

@kujiy a2enmod proxy_http helped me with the same problem, thx :)

[Chris Giddings]

The slash is all I required. Is there a technical reason to quote the URL pattern and the balancer reference?

[Christopher Schultz]

@ChrisGiddings I tend to quote everything that might possibly contain a space. I also tend to script lots of things, so it's very possible NOT quoting something won't be obvious when adding a space to a value that might end up in there.

[Chris Giddings]

@ChristopherSchultz That's entirely reasonable. I also tend to script quite a bit, but I've never done so within a balancer reference. It just caught my attention. :)

[Abhishek Prabhat]

a2enmod proxy proxy_http helped me.