One of our EBS R12 was inaccessible and was throwing generic http-404 erorr for the login page. On the application side adopmnctl was showing status ACTIVE for all the required procesees.
Simple HTML file like http://<server_name>:<port>/OA_HTML/test.html was also not opening means it was Apache issue or Oacore issue since definition of OA_HTML in html link is given by OACORE.
Error message in the Browser was like below:
Not Found
The requested URL /OA_HTML/test.html was not found on this server.
In one of the Apache server log we were able to see that it is trying to find the file under portal directory which is not the correct place
</EXEC_CONTEXT_ID>
</CORRELATION_DATA>
<PAYLOAD>
<MSG_TEXT>File does not exist: /fs01/<SID>/inst/apps/<CONTEXT_NAME>/portal/OA_HTML/test.html</MSG_TEXT>
</PAYLOAD>
</MESSAGE>