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JOTN
Asked: 2010-11-29 08:21:39 +0800 CST

Intermittent error when using mod_proxy to do reverse proxy to SOAP service

  • 772

I get this error every few minutes when using mod_proxy as a reverse proxy to a SOAP web service. There's probably 3 or 4 requests going per seconds so we're talking around 1 or 2 out of every thousand that have this error.

[Tue Nov 23 11:44:14 2010] [error] [client 172.16.1.31] (20014)Internal error: proxy: error reading status line from remote server soap1.server:8888
[Tue Nov 23 11:44:14 2010] [error] [client 172.16.1.31] proxy: Error reading from remote server returned by /someapp/path/to/web/service

This causes the request to fail. If I have the client connect directly to the soap server without using the proxy, success is 100% so the problem appears to be in the proxy

The configuration looks like this. The purpose is to switch to a backup server if the primary one is unavailable:

<Proxy balancer://apicluster>  
BalancerMember http://soap1.server:8888 lbset=0 
BalancerMember http://soap2.server:8888 lbset=1 
</Proxy>  

ProxyPass /someapp balancer://apicluster/someapp 
ProxyPassReverse / balancer://apicluster/someapp

Has anyone run into this and found a fix? There's some mentions in bug reports but no solutions. The only thing that may be unusual is the client request could be 100MB or larger, so the request could take a little longer than you'd expect for a SOAP call.

apache-2.2 mod-proxy

3 Answers

  1. Best Answer

    In case someone else runs into this. This is a bug in mod_proxy that can be avoided by putting these lines in your httpd.conf:

    SetEnv force-proxy-request-1.0 1
SetEnv proxy-nokeepalive 1

    https://issues.apache.org/bugzilla/show_bug.cgi?id=37770

    For info on what these variables do see the mod_proxy documentation. They have a specific section, Protocol Adjustment, that addresses these variables.

    • 28

  2. Take note of the Apache documentation here: http://httpd.apache.org/docs/2.2/mod/mod_proxy_http.html

    It seems there is a race condition in mod_proxy_http, but it can be avoided by including:

    SetEnv proxy-initial-not-pooled 1

    Which prevents Apache using a pooled connection if this is an initial request.

    The document does note that this setting will give a performance downgrade.

    • 5

  3. You can also suppress this related error message (AH01102: error reading status line from remote server) by using the apache module mod_reqtimeout and this conf directive:

    RequestReadTimeout header=30

    You'll likely have to enable the reqtimeout module, as follows:

    $ sudo a2enmod reqtimeout
$ sudo apache2ctl restart
    • 0