config.xml is the central configuration repository for a domain. every resource you have configured from admin console or by command line or by any other tool registered under this file. WLS 9.x onwards, this file contain references to other XML configuration files also those are under your domain/config folder ( further subfolder under it for respective resources ) since wls 9.x onwards concept of modules are introduced for sub-resources like data source, JMS etc otherwise prior to 9.x ( 8.x or older ) every configuration was stored under this single config.xml file
When you create a domain, the Configuration Wizard prompts you to provide the username and password for an initial administrative user. If you create the domain in development mode, the wizard saves the username and encrypted the password in a boot identity file. A WebLogic Server instance can refer to a boot identity file during its startup process. If a server instance does not find such a file, it prompts you to enter credentials. If you create a domain in production mode, or if you want to change user credentials in an existing boot identity file, you can create a new boot identity file.
A WebLogic Server cluster consists of multiple WebLogic Server server instances running simultaneously and working together to provide increased scalability and reliability. A cluster appears to clients to be a single WebLogic Server instance. The server instances that constitute a cluster can run on the same machine, or be located on different machines. You can increase a cluster’s capacity by adding additional server instances to the cluster on an existing machine, or you
can add machines to the cluster to host the incremental server instances. Each server instance in a cluster must run the same version of WebLogic Server.
Any external access to EJB is not allowed. if the apache web server already configures as front-end. then we need to lookup by JNDI tree.
If managed server is in FAILED State there could be reason as follows: