* HTTP_Server on middle tier is different from HTTP_Server on Infra tier (later is used for Single Sign-On)

Once you are sure that all services are up & running now follow below procedure

2. Check Web Cache - When User type URL for Oracle Portal which is of format http://hostname.domainname:port/pls/portal request first hits web-cache($ORACLE_HOME/webcache) on middle tier. So check if request is hitting till web-cache by checking $ORACLE_HOME/webcache/access_log   , access_log will record any request coming to web cache.   

For any issues on Web Cache check $ORACLE_HOME/webcache/event_log . If you don’t see request in access_log in under $OH/webcache/logs directory, check firewall or load balancer configuration (If Load Balancer is configured)

3. Check OHS - Oracle HTTP Server ->  Web-cache then forward this request to Origin Server which is listening on different port (usually one higher than Web Cache Listen Port). This request is against recorded in access_log but this time access_log of OHS which is under $ORACLE_HOME/Apache/Apache/logs/  so check if you see request coming from web cache to OHS.
  For any issues in OHS check logs at error_log & error_log_pls in above directory.

4. OHS mod_rewrite -> Oracle HTTP Server (OHS) checks in httpd.conf to see where /pls/portal maps. In httpd.conf there is redirect rule which redirect any /pls/portal to /portal/.. like (RewriteRule (^/pls/portal$) /portal [PT]) so request to HTTP Server (Apache Server) internally changes to /portal..

5. OHS to OC4J_Portal-> Apache again try to find where /portal maps which is defined in file ($ORACLE_HOME/Apache/Apache/conf/mod_oc4j.conf ) entry like

    Oc4jMount /portal OC4J_Portal
    Oc4jMount /portal/* OC4J_Portalwhich means request will hit be served by OC4J_Portal hence OHS forwards request to OC4J_Portal

6. OC4J_Portal then goes to database and pulls out various portion of page (header, footer, sidebar - depending on how you user has defined portal page) from database.

For any issues in OC4J_Portal check logs at $ORACLE_HOME/j2ee/OC4J_Portal/application-deployments/portal/
OC4J_Portal_default_island_1/application.log
and
$ORACLE_HOME/j2ee/OC4J_Portal/log/
OC4J_Portal_default_island_1/server.log 

7. Parallel Page Engine (PPE) component in OC4J then assemble this page and return it back to user.

Stay tuned for process flow in Oracle Single Sign-On and steps on how to troubleshoot Oracle Single Sign-On Issues …..