What is proxy server

A proxy server seats between the client browser and the servers behind it, it intercepts the client request and then connects to the backend server using its own connection pool, forwards clients request to the server, gets response back from the back end server and then returns that response back to the client. A proxy server performs the same basic duties as a web server and in addition to that they perform following things

• Proxy: Accepts requrest from the client, forwards that request to backend, gets response back and forwards that response to client. In doing so it hides the actual back end server information from the client


• Content filtering: They are often used to filter access to internet. The proxy can be configured with rules to reject access to sites that contain objectionable material, preventing users from gaining access to those sites


• Caching: Proxy servers can cache the results of common user requests and next time they get request for that resource, they can server the response from cache instead of sending to the actual backend server


• Security: They terminate the user connection inside the DMZ, they hide server identities by providing thier own domain names in the URL instead of backend server name. Combined with authentication proxy such as TAM, proxies can authenticate the user before forwarding the request to backend

Installapp option during node federation

When you federate node to a cell, any existing installed enterprise applications are uninstalled as part of federation process. If you wish to federate any existing user-installed applications into the cell, you can specify the -installapp command line argument when invoking addNode or you can select the Include applications check box if using the WAS Admin console for adding new node. If selected an attempt will be made to copy the applications installed on the application server instance into the cell, but applications with same name as applications that are currently installed into the cell will not be federated into the cell configuration

WAS ND Architecture main components

Deployment Manager
The Deployment Manager process provides a centralized administration mechanism for all nodes in a cell, including all WAS processes on each nodes as well as the cell configuration repository for both WAS and installed applications. The Dmgr works in conjunction with each node agent to control processes on each node and to maintain the configuration for each node. By providing a central point for management, the Dmgr allows you to control cells consisting of numerous nodes and in turn nodes running one or more server.

Node agent

A node agent is a local administrative agent process running on every node in the cell. The node agent server acts as local proxy for deployment manager, providing capability to manage servers and the configuration for each servers defined on a node. The node agent is intended solely as an administative process, the node agent does not provide a J2EE application runtime.If you use wsadmin tool to directly connect to node agent then you will only get access to AdminControl functions, AdminConfig and AdminApp functions are not available to safeguard against accidental changing of the configuration data

Application server
Application server in ND environment is same as the application server in standalone environment, but the difference is that it does not have a Administrative console application, instead configuration for the application server is managed centerally by the Deployment Manager. If you use wsadmin tool to directly connect to application server then you will only get access to AdminControl functions, AdminConfig and AdminApp functions are not available to safeguard against accidental changing of the configuration data

JMS Server
This server hosts the WebSphere Embedded messaging service on a node. In WAS ND there can be one JMS server node.

Admin Client
WAS provides two different admin clients, one is Web based Admin console and other is wasadmin command which is a command line tool

Managed vs unmanaged processes

A node is a logical grouping of managed servers. A node usually corresponds to a logical or physical computer system with a distinct IP host address. Nodes cannot span multiple computers.

Nodes in the network deployment topology can be managed or unmanaged. A managed node has a node agent process that manages its configuration and servers. Unmanaged nodes do not have a node agent.

A managed node has a node agent that manages all servers on a node, whether the servers are WebSphere Application Servers, Java Message Service (JMS) servers (on Version 5 nodes only), Web servers, or generic servers. The node agent represents the node in the management cell and keeps the configuration up to date.

1. Managed node: A managed node has a node agent that manages all servers on a node, whether the servers are WebSphere Application Servers, Java Message Service (JMS) servers (on Version 5 nodes only), Web servers, or generic servers. The node agent represents the node in the management cell and keeps the configuration up to date. All WAS processes are called managed servers or managed processes, meaning that all are parto f a single administration domain (cell) and results can be centerally managed and monitored. In WAS following processes are managed process
   
   
   
   • Deployment Manager
   
   
   • Node Agent
   
   
   • Application Server
   
   
   • JMS Server
   
   
   
   


2. Unmanaged nodes: An unmanaged node does not have a node agent to manage its servers. Unmanaged nodes in the Network Deployment environment can have server definitions such as Web servers, but not Application Server definitions. Unmanaged nodes in the Network Deployment environment cannot have a node agent added to it, and therefore cannot become a managed node. In the stand-alone Application Server environment, nodes do not have node agents and are also considered unmanaged nodes. The deployment manager cannot manage a stand-alone Application Server because it is not known to the cell. A stand-alone Application Server can be federated. When it is federated, a node agent is automatically created, and the node becomes a managed node in the cell.

A supported Web server can be on a managed node or an unmanaged node. You can define only one Web server to a stand-alone WebSphere Application Server node. This Web server is defined on an unmanaged node. You can define Web servers to the deployment manager. These Web servers can be defined on managed or unmanaged nodes.