1.DNS
The Domain Name System (DNS) is a hierarchical naming system for computers, services, or any resource participating in the Internet or web services. It is associated with various information with domain names assigned to such participants. Most importantly, it translates domain names into the numerical (binary) identifiers associated with networking equipment for the purpose of locating and addressing these devices world-wide.
DNS is basically a database of all domain names registered in a top level domain. A registry operator also known as Network Information Centre (NIC), is a part of the DNS of the Internet or the Web Services or Web Applications that the server holds in its domain. It maps domain names to IP addresses. Each NIC is an organization that manages a registration of Domain Names within the top-level-domains for which it is responsible, controls the policies of the domain name allocation, and technically operates its top level domain.
Domain names are managed under a hierarchy headed by the Internet Assigned Numbers Authority (IANA), which manages the top of the DNS tree by administrating the data in the root nameservers.
2. Resources Used by Managed Servers
A domain contains the resources and services that Managed Servers and Deployed Applications require. Managed Servers can use the following resources:
· Machine definitions that identify a particular, physical piece of hardware. A machine definition is used to associate a computer with the Managed Servers it hosts. This information is used by Node Manager in restarting a failed Managed Server, and by a clustered Managed Server in selecting the best location for storing replicated session data.
· Network channels that define default ports, protocols, and protocol settings that a Managed Server uses to communicate with clients. After creating a network channel, you can assign it to any number of Managed Servers and clusters in the domain.
· Virtual hosting, which defines a set of host names to which WebLogic Server instances (servers) or clusters respond. When you use virtual hosting, you use DNS to specify one or more host names that map to the IP address of a server or cluster.
Applications can use the following resources and services:
a) Security providers, which are modular components that handle specific aspects of security, such as authentication and authorization.
b) Resource adapters, which are system libraries specific to Enterprise Information Systems (EIS) and provide connectivity to an EIS.
c) Diagnostics and monitoring services.
d) JDBC data sources, which enable applications to connect to databases.
e) Mail sessions.
f) XML entity caches and registry of XML parsers and transformer factories
g) Messaging services such as JMS servers and store-and-forward services
h) Persistent store, which is a physical repository for storing data, such as persistent JMS messages. It can be either a JDBC-accessible database or a disk-based file.
i) Startup classes, which are Java programs that you create to provide custom, system-wide services for your applications.
j) Managers, which determine how an application prioritizes the execution of its work based on rules you define and by monitoring actual runtime performance. You can create Work Mangers for entire WebLogic Server domains or for specific application components.
k) Work Contexts, which enable applications to pass properties to a remote context without including the properties in a remote call.
3. Web server load balancing
Web server load balancing is useful for queuing and throttling requests. For the Weblogic Server, the most commonly used method for load balancing is Round-Robin DNS.
Round-Robin DNS is a relatively simple method of load balancing, where a Domain Name System (DNS) server provides a name to address resolution and is always involved when a host name is included in a URL. A Round-Robin DNS server can resolve one single host name into multiple IP addresses, such that requests for a single URL (containing a host name) actually reference different web servers. The client requests a name resolution for the host name but, in fact, receives different IP addresses, thus spreading the load among the web servers. In a simple configuration, the Round-Robin DNS server cycles through the list of available servers.
