Concepts

Standalone WAS server

The heart of WAS installation is the application server itself.
The application server in-turn contains the following services/containers:

1. Admin server - maintains and manages the adminstration repository (configuration as xml files).It accepts requests from the admin console and also from wsadmin commands.
2. Web container - runtime environment for servlets, jsps, etc.
3. Embedded HTTP server (EHS) 
4. Web services engine
5. EJB container
6. J2C service
7. JNDI naming service
8. Messaging engine - provides functionality of Service integration bus.
9. Security service

Concept of profiles

A profile defines the runtime environment.

The profile includes all the files that the server loads in the runtime environment and that you can change. They share core product files. A profile contains its own set of scripts, its own environment, and its own repository. Each profile is stored in a unique directory path selected by the user at profile creation time.

Starting from WAS v6.0, a application server always runs on a profile (either the one you created or the default profile).
You can create a runtime environment either through the manageprofiles command or the Profile Management Tool graphical user interface.

Why Profiles?

Not only is disk space saved, but updating the product is simplified when you maintain a single set of product core files. (core product files are the shared product binary files, which are shared by all profiles) Also, creating new profiles is more efficient and less prone to error than full product installations, allowing a developer to create separate profiles of the product for development and testing.

Node

A node is an administrative grouping of application servers for configuration and operational management within one operating system instance. (except in the case of virtualization where you have multiple operating systems in a single physical machine).
It is possible to create multiple nodes inside one operating system instance, but a node cannot leave the operating system boundaries and so creating multiple nodes on one OS instance is possible but doesn't improve performance or reliability in any way.
A Node cannot span multiple computers(or OS instances).

Nodes can be managed or unmanaged.
Unmanaged nodes are those that are not federated to DMGR. An example would be a standalone application server's node.
Managed nodes are those that are federated to DMGR with the help of a node agent.

Read more about nodes here


Node agent

An administrative agent that manages all application servers on a node and represents the node in the management cell.
A node agent is created automatically when you add (federate) a stand-alone node to a cell. Node agents takes the responsibility of synchronizing the individual configuration of nodes with their master configuration.


Cell

A cell is a grouping of nodes into a single administrative domain. This administrative domain is made possible with the installation of a deployment manager.


Deployment Manager (DMGR)

It is the central administration point of a cell that consists of multiple nodes and node groups in a distributed server configuration. The deployment manager uses the node agent to manage the application servers within one node. DMGR helps to manage not only just WAS Nodes but also HTTP servers, clusters, etc.


Cluster

A cluster is a logical collection of application server processes that provides workload balancing and high availability. Application servers that belong to a cluster are members of that cluster and must all have identical application components deployed on them.

The difference between Node and Cluster is that the Node decides where the JVM’s should run whereas the Cluster is just a mere pointer to the JVM’s. Also a single Cluster can point to a local application server(vertical clustering) and/or a remote server(horizontal clustering) where a single Node holds either local or remote and not both.