502 Bad Gateway is a standard http error code.  Although it implies that there is a fault with the network gateway itself, in fact the issue is that a server somewhere between the client and the destination has received a response that it doesn't understand.

For example, the gateway might receive an unexpected response from the application server:

Or, in a more complex network, a gateway might receive an unexpected response from another server along the path:

While a 502 error problem is 'in progress' the message can appear in a Internal Audit client error message and will also be shown simply by browsing to a file on the server, e.g. https://server.domain.com/[Instance_Name]/WebUI.  Browsing to a URL from various machines/points on the network can be useful in trying to pinpoint the issue in the system.

Where Internal Audit is hosted by Ideagen

A whitelist problem?

Where the application is hosted by Ideagen, this error is almost always caused by an issue with an IP whitelist.  Typically:

• The customer asks us to restrict access to the server to a set of IP addresses
• At some point later, the IP addresses used by the customer change, or one or more users attempt to connect from a new location

This can mean that some or all users are affected.

The IP address restriction mechanism is maintained by our CloudOps team.  If a change to the whitelisted IP address list is required then:

• Verify the IP addresses that need to be whitelisted
• The support team should escalate the issue to CloudOps, who will update the whitelist accordingly

A binding problem?

If whitelists are not used, then the error occurs due to missing https bindings on the web site:

• https bindings should be reinstated
• ensure that the certificate selected for the binding is valid and trusted by the server

A certificate problem?

Rarely, we have seen cases where an expired SSL certificate may cause this problem:

• In IIS Manager, open the bindings dialog and view the certificate assigned to the https binding, checking for validity

Further information

Ideagen support engineers can find more information on IP whitelisting in the hosting system here:

Maintaining hosted customers' IP address whitelists