Login flow in R12.2

Login flow in R12.2
When a HTTP request is made for EBS, the request is received by the Oracle HTTP Server (OHS).
When the configuration of OHS is for a resource that needs to be processed by Java, such as logging into EBS, the OHS configuration will redirect the request to the Web Logic Server (WLS) Java process (OACore in this case).
WLS determines the J2EE application that should deal with the request, which is called “oacore”.
This J2EE application needs to be deployed and available for processing requests in order for the request to succeed.   The J2EE application needs to access a database and does this via a datasource which is configured within WLS.
Here is the processing in terms of URL(Login HTTP headers)
When the EBS login works OK, the browser will be redirected to various different URLs in order for the login page to be displayed.  The page flow below shows the URLs that will be called to display the login page:
/OA_HTML/AppsLogin
EBS Login URL
/OA_HTML/AppsLocalLogin.jsp
Redirects to local login page
/OA_HTML/RF.jsp?function_id=1032925&resp_id=-1&resp_appl_id=-1&security_group_id=0&lang_code=US&oas=3TQG_dtTW1oYy7P5_6r9ag..&params=5LEnOA6Dde-bxji7iwlQUg
Renders the login page
The URLs after the user enters username and password, then clicks the “login” button are shown below:/OA_HTML/OA.jsp?page=/oracle/apps/fnd/sso/login/webui/MainLoginPG&_ri=0&_ti=640290175&language_code=US&requestUrl=&oapc=2&oas=4hoZpUbqVSrv9IE0iJdY1g..
/OA_HTML/OA.jsp?OAFunc=OANEWHOMEPAGE
/OA_HTML/RF.jsp?function_id=MAINMENUREST&security_group_id=0
Renders user home page
Once the users home page is displayed, the logout flow also redirects to several different URL before returning to the login page:
/OA_HTML/OALogout.jsp?menu=Y
Logout icon has been clicked
/OA_HTML/AppsLogout
/OA_HTML/AppsLocalLogin.jsp?langCode=US&_logoutRedirect=y
Redirects to the login page
/OA_HTML/RF.jsp?function_id=1032925&resp_id=-1&resp_appl_id=-1&security_group_id=0&lang_code=US&oas=r6JPtR7-a4n5U2H3–ytEg..&params=1JU-PCsoyAO7NMAeJQ.9N6auZoBnO8UYYXjUgSPLHdpzU3015KGHA668whNgEIQ4
Renders login page again
Basic Troubleshooting for Login in R12.2
1)  OHS (apache) failure
If OHS is not running or not responding, one would see a message as below. If OHS is not running then there will not be any messages in any EBS log file for this request.
Firefox: “The connection was reset”
Steps to take
Check OHS has started OK
adapcctl.sh status
adapcctl.sh stop
adapcctl.sh start
2  OACore JVM process not available
If the OACore JVM is not running or not reachable, then one will likely see the following message in the browser:
Failure of server APACHE bridge:
No backend server available for connection: timed out after 10 seconds or idempotent set to OFF or method not idempotent.
There could be two reason
Steps to take
a)Make sure the OACore JVM has started correctly
admanagedsrvctl.sh start oacore
b) Check mod_wl_ohs.conf file is configured correctly
3) oacore J2EE application not available
There may be cases where the OACore JVM is running and reachable but the oacore application is not available.
The browser will report the error:
Error 404–Not Found
From RFC 2068 Hypertext Transfer Protocol — HTTP/1.1:
10.4.5 404 Not Found
The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent.
Access_log will show 404 error:
GET /OA_HTML/AppsLogin HTTP/1.1″ 404
Steps to take
In the FMW Console check the “deployments” to confirm the “oacore” application is at status “Active” and Health is “OK”.
4) Datasource failure
The oacore logs will show this type of error
<Error> <ServletContext-/OA_HTML> <BEA-000000> <Logging call failed exception::
java.lang.NullPointerException
at oracle.apps.fnd.sso.AppsLoginRedirect.logSafe(AppsLoginRedirect.java:639)
at oracle.apps.fnd.sso.AppsLoginRedirect.doGet(AppsLoginRedirect.java:1314)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:707)
The explorer will show
The system has encountered an error while processing your request.Please contact your system administrator
Steps to Take
Review the EBS Datasource and make sure it is targeted to the oacore_cluster1 managed server.   Also use the “Test Datasource” option to confirm database connection can be made
If one makes any changes, one will need to restart the managed server, despite FMW Console saying no restart is necessary.