Oracle HTTP Server High Availability Architecture and Failover Considerations Oracle HTTP Server Protection from Failures and Expected Behaviors

Configuring High Availability for Web Tier Components 9-7 ■ Access logs, which record which components and applications are being accessed, and by whom. You can view Oracle Fusion Middleware log files using either Oracle Fusion Middleware Control or a text editor. The log files for Oracle HTTP Server are located in the following directory: ORACLE_INSTANCEdiagnosticslogsOHSOHS_NAME. The default name of a log file is ohs_name.log. For more information about Oracle HTTP Server log files, see the Oracle Fusion Middleware Administrator’s Guide for Oracle HTTP Server.

9.2.6 Oracle HTTP Server High Availability Architecture and Failover Considerations

Figure 9–2 shows two Oracle HTTP Servers, which have been placed behind a load balancer. The load balancer receives requests from users and forwards them on to the connected Oracle HTTP Servers. In the example, the Load Balancer receives the requests on the standard HTTPHTTPS ports 80443, however, it then passes them on to the Oracle HTTP Servers using completely different ports. This has the following advantages: ■ Actual ports are hidden from users. ■ Users do not have to add the port numbers to the URL. On Unix-based systems, it is not mandatory to start Oracle HTTP Server with root privileges. Only root can start a process which uses a port less than 1024. The load balancer routes requests to the functioning Oracle HTTP Servers. Figure 9–2 Oracle HTTP Server High Availability Architecture Figure 9–2 also shows how Oracle HTTP Server distribute requests to Web Logic Managed Servers. For High Availability, it is assumed that each pair of components Oracle HTTP Server and Web Logic Managed Servers exist on different hosts. This architecture could simply be separated across two servers. Alternatively, in more complex implementations, each component could be located on a completely separate server. Load Balancer myapp.mycompany.com https:7777 https:7777 https:7075 https:7075 https:443 http:80 WebLogic Managed Server OHS 1 WebLogic Managed Server OHS 2 9-8 Oracle Fusion Middleware High Availability Guide

9.2.7 Oracle HTTP Server Protection from Failures and Expected Behaviors

Oracle HTTP Servers failures can be divided into two categories: process failures and node failures. Individual operating system process may fail, where as node failures are involve the entire host upon which the Oracle HTTP Server failing. Process Failure The Oracle HTTP Server processes are protected by the Oracle Process Manager and Notification system OPMN. If an Oracle HTTP Server process fails, OPMN automatically restarts the process. Node Failure If an entire node fails, the load balancer or Oracle Web Cache, in front of Oracle HTTP Server, sends a request to another Oracle HTTP Server if the first one does not respond, or is determined to be failed through URL pings. WebLogic Managed Server Failure In a high Availability deployment, Oracle WebLogic managed servers are part of a cluster. If one of the managed servers fails, mod_wl_ohs automatically redirects requests to one of the active cluster members. If the application stores state, state replication is enabled within the cluster, which allows redirected requests access to the same state information. Database Failure Database failures are only likely to be an issue where mod_oradav or mod_plsql is used. If this is an Oracle Real Application Clusters Oracle RAC database, the failure characteristics are determined by the defined Oracle RAC connection. If client connection failover is configured, any in-flight transactions are rolled back, and a database reconnection is required. If Transparent Application Failover TAF is configured, any in-flight database write is rolled back, but an automatic database reconnection takes place, and select statements are automatically recovered. In this scenario, TAF only fails over select statements, and package variables are lost.

9.2.8 Oracle HTTP Server Cluster-Wide Configuration Changes