502 Proxy Errors when accessing databases through WAM – SVSU Library Help Center

Description

The cause and remedy for certain 502 errors encountered when using WAM.

Symptoms

Getting the following 502 proxy error when trying to access a database through Web Access Management (WAM):

The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request [specific error]

Cause

WAM caches a successful connection so that multiple DNS lookups are not required during a database session. This works well unless a database vendor has multiple IPs for the same domain name, as is the case now that many database vendors are using load balancers and multiple servers in the cloud.

In a proxied connection, WAM will cache the IP for the first successful connection. If the connection is then redirected to a different IP, and the first connection is no longer accessible, you may get a 502 error. In this case, restarting the webpacs will clear the cached entries and you usually will be able to connect. Be aware that many browsers also cache results so in some cases you would need to also clear your browser's cache and cookies.

Here is more detailed information on the WAM cache file:

The wam_dns file is a binary file used by webpac to cache successful IP address connections in Web Access Management. This file allows webpac to do multiple DNS lookups for the same IP address during consecutive requests to the same destination. Webpac considers file entries older than 24 hours to be stale and refreshes entries if webpac does a lookup on the entry's IP address.

Resolution

Restarting all webpac processes will clear the WAM cache and usually results in restored access. You may also need to clear your browser.

Instructions for restarting webpacs in Sierra can be found in Sierra WebHelp:
http://csdirect.iii.com/sierrahelp/Default.htm#sgcir/sgcir_admin_restartsession.html

Instructions for restarting the webpacs in Millennium can be found in the IGR, page 105634:
http://csdirect.iii.com/manual/i_webopac_restart.html

NOTE: Innovative's Product Management is continually reviewing the WAM caching process, but restarting webpacs when these 502 errors occur is recommended.