When upgrading the NetWitness Platform from 11.4.x to 11.5.x or 11.6.x, the NetWitness Platform can fail with a post upgrade HTTPS Error 504 - Gateway Timeout. This error can appear in the browser as well as in the node-infra-server.log.
What can cause this issue is an upgrade failure due to having proxy settings enabled in the /etc/yum.conf and/or the /etc/environment file.
To address this issue, there are two options possible based on what is required of the environment. Note: Both options are performed against the Admin Server (Node 0)
Removing/Disabling Proxy Settings
If the proxy server settings can be removed from NetWitness and the upgrade can still function, follow the steps below.
Open /etc/yum.conf file and remove the proxy setting. Example: proxy=<proxy-url>