I am trying to configure a reverse proxy with apache, but I am getting a No protocol handler was valid for the URL error, which I do not understand.

This is the relevant configuration of apache:

ProxyRequests Off
ProxyPreserveHost On

<Proxy *>
       Order deny,allow
       Allow from all

ProxyPass        /gonvaled/examples/jsonrpc/output/services/ http://localhost:8000/services/
ProxyPassReverse /gonvaled/examples/jsonrpc/output/services/ http://localhost:8000/services/

The requests is reaching apache as:

POST /gonvaled/examples/jsonrpc/output/services/EchoService.py HTTP/1.1

And they should be forwarded to my internal service, located at:

These are the logs:

==> /var/log/apache2/error.log <==
[Wed Jun 20 02:05:20 2012] [debug] proxy_util.c(1506): [client] proxy: http: found worker http://localhost:8000/services/ for http://localhost:8000/services/EchoService.py, referer: http://localhost/gonvaled/examples/jsonrpc/output/JSONRPCExample.safari.cache.html
[Wed Jun 20 02:05:20 2012] [debug] mod_proxy.c(998): Running scheme http handler (attempt 0)
[Wed Jun 20 02:05:20 2012] [warn] proxy: No protocol handler was valid for the URL /gonvaled/examples/jsonrpc/output/services/EchoService.py. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.
[Wed Jun 20 02:05:20 2012] [debug] mod_deflate.c(615): [client] Zlib: Compressed 614 to 373 : URL /gonvaled/examples/jsonrpc/output/services/EchoService.py, referer: http://localhost/gonvaled/examples/jsonrpc/output/JSONRPCExample.safari.cache.html

==> /var/log/apache2/access.log <== - - [20/Jun/2012:02:05:20 +0200] "POST /gonvaled/examples/jsonrpc/output/services/EchoService.py HTTP/1.1" 500 598 "http://localhost/gonvaled/examples/jsonrpc/output/JSONRPCExample.safari.cache.html" "Mozilla/5.0 (X11; Linux i686) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.162 Safari/535.19"

I found the problem. The proxy_http module needs to be activated too in Apache (I had only proxy_html and proxy)


For me, on apache httpd 2.4, this happened because i was missing the trailing slash:

Did not work:

    <Proxy balancer://mycluster>
    ProxyPass / balancer://mycluster
    ProxyPassReverse / balancer://mycluster


    <Proxy balancer://mycluster>
    ProxyPass / balancer://mycluster/
    ProxyPassReverse / balancer://mycluster/

(added / at the end)

  • For me, apache 2.2.15, <kbd>/</kbd> at the end works. THX! – user580056 Apr 7 '16 at 7:18
  • helped me on Apache/2.4.10 (Debian). This needs to be documented! The error message is extremely obtuse – DeveloperChris Oct 11 '16 at 2:39

For those that come looking for answers, another possibility is the URL service name to backend too is missing. With LogLevel Debug, and mod_proxy and mod_proxy_fcgi, I was seeing the following:

[debug] proxy: fgci: found worker fgci:// [debug] mod_proxy.c(1026): Running scheme fgci handler (attempt 0) [debug] mod_proxy_fcgi.c(800): [client ...] AH01076: url: fgci:// proxyname: (null) proxyport: 0 [debug] mod_proxy_fcgi.c(805): [client ...] AH01077: declining URL fgci:// [warn] proxy: No protocol handler was valid for the URL /.../index.php. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.

Thankfully the code for mod_proxy_fastcgi (I'm using a backport for Apache 2.2 on RHEL6) is available at https://github.com/ceph/mod-proxy-fcgi/blob/master/mod_proxy_fcgi.c#L805, which is this piece of code:

if (strncasecmp(url, "fcgi:", 5) != 0) {
    ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r, APLOGNO(01077) "declining URL %s", url);
    return DECLINED;

If you look closely at the logs -- I only noticed it when looking at the code that issues the message -- you'll see that what should be fcgi://... is misspelt as fgci://...

So when you see declining URL it means either:

  • You don't have a handler loaded that accepts the service (eg. fcgi:), or
  • you have misspelt the service name.
  • 1
    I upvoted because of the "When you see this error it means..." portion of this answer. I feel that this should lead most searchers in the right direction. – threeve Aug 8 '17 at 19:39

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