Network Deployment (Distributed operating systems), v8.0 > Applications > Naming and directory > Naming


Namespace logical view

The namespace for the entire cell is federated among all servers in the cell. Every server process contains a name server. All name servers provide the same logical view of the cell namespace. The various server roots and persistent partitions of the namespace are interconnected by a system namespace. We can use the system namespace structure to traverse to any context in a cell's namespace.

The bindings in the preceding diagram appear with solid arrows, labeled in bold, and dashed arrows, labeled in gray. Solid arrows represent primary bindings. A primary binding is formed when the associated subcontext is created. Dashed arrows show linked bindings. A linked binding is formed when an existing context is bound under an additional name. Linked bindings are added for convenience or interoperability with previous WAS versions.

A cell namespace is composed of contexts which reside in servers throughout the cell. All name servers in the cell provide the same logical view of the cell namespace. A name server constructs this view at startup by reading configuration information. Each name server has its own local in-memory copy of the namespace and does not require another running server to function. There are, however, a few exceptions. Server roots for other servers are not replicated among all the servers. The respective server for a server root must be running to access that server root context.

In WAS Network Deployment cells, the cell and node persistent areas can be read even if the dmgr and respective node agent are not running. However, the dmgr must be running to update the cell persistent segment, and a node agent must be running to update its respective node persistent segment.


Namespace partitions

There are five major partitions in a cell namespace:

System namespace partition

Contains a structure of contexts based on the cell topology. The system structure supports traversal to all parts of a cell namespace and to the cell root of other cells, which are configured as foreign cells. The root of this structure is the cell root. In addition to the cell root, the system structure contains a node root for each node in the cell. We can access other contexts of interest specific to a node from the node root, such as the node persistent root and server roots for servers configured in that node.

All contexts in the system namespace are read-only. We cannot add, update, or remove any bindings.

Server roots partition

Each server in a cell has a server root context. A server root is specific to a particular server. We can view the server roots for all servers in a cell as being in a transient read/write partition of the cell namespace. System artifacts, such as enterprise bean (EJB) homes for server applications and resources, are bound under the server root context of the associated server. A server application can also add bindings under its server root. These bindings are transient. Therefore, the server application creates all required bindings at application startup, so they exist anytime the application is running.

A server cluster is composed of many servers that are logically equivalent. Each member of the cluster has its own server root. These server roots are not replicated across the cluster. In other words, adding a binding to the server root of one member does not propagate it to the server roots of the other cluster members. To maintain the same view across the cluster, you should create all user bindings under the server root by the server application at application startup so that the bindings are present under the server root of each cluster member. Because of Workload Management (WLM) behavior, a JNDI client outside a cluster has no control over which cluster member's server root context becomes the target of the JNDI operation. Therefore, you should execute bind operations to the server root of a cluster member from within that cluster member process only.

Server-scoped configured name bindings are relative to a server's server root.

The name of a cluster member must be unique within a cell and must be different from the cell name.

Cell persistent partition

The root context of the cell persistent partition is the cell persistent root. A binding created under the cell persistent root is saved as part of the cell configuration and continues to exist until it is explicitly removed. Applications that need to create additional persistent bindings of objects generally associated with the cell can bind these objects under the cell persistent root.

It is important to note that the cell persistent area is not designed for transient, rapidly changing bindings. The bindings are more static in nature, such as part of an application setup or configuration, and are not created at run time.

The cell persistent area can be read even if the dmgr is not running. However, the dmgr must be running to update the cell persistent segment. Because every server contains its own copy of the cell persistent partition, any server can look up locally objects bound in the cell persistent partition.

Cell-scoped configured name bindings are relative to a cell's cell persistent root.

Node persistent partition

The node persistent partition is similar to the cell partition except that each node has its own node persistent root. A binding created under a node persistent root is saved as part of that node configuration and continues to exist until it is explicitly removed.

Applications that need to create additional persistent bindings of objects associated with a specific node can bind those objects under that particular node's node persistent root. As with the cell persistent area, it is important to note that the node persistent area is not designed for transient, rapidly changing bindings. These bindings are more static in nature, such as part of an application setup or configuration, and are not created at run time.

The node persistent area for a node can be read from any server in the node even if the respective node agent is not running. However, the node agent must be running to update the node persistent area, or for any server outside the node to read from that node persistent partition. Because every server in a node contains its own copy of the node persistent partition for its node, any server in the node can look up locally objects bound in that node persistent partition.

Node-scoped configured name bindings are relative to a node's node persistent root.

Applications partition

The Java EE 6 specification introduces module, application, and global namespaces. Java URL JNDI names that have the prefixes...

  • java:module
  • java:app
  • java:global

...can access the respective namespaces. In some situations, the namespaces are only locally accessible, and in other situations the namespaces are remotely accessible.

The applications partition contains namespaces that are remotely accessible. The root of the java:global namespace is the applications root context. The roots of other namespaces are under the subcontext...

    com.ibm.ws.AppNameSpaces

For example, the java:app root context for the application, MyApp, is bound with the name...

    MyApp/root

...relative to...

    com.ibm.ws.AppNameSpaces

Module and component namespaces are only accessible remotely when the module is a client module in a server-deployed mode or in a federated mode. For example, the java:module root context for the server-deployed client module MyClientModule in the application MyApp is bound with the name...

    MyApp/MyClientModule/root

...relative to...

    com.ibm.ws.AppNameSpaces

The component namespace, which contains comp/env bindings, for that same module is bound under...

    MyApp/MyClientModule/ClientComponent/root

...relative to...

    com.ibm.ws.AppNameSpaces

Application resources, such as EJB references, resource references, and environment entries, with java:global names are bound into the java:global namespace when the defining application is installed. The application does not need to be running for those name bindings to be available to other applications.

Resources defined in applications with java:global names are bound in the application partition for all servers in the cell when the data is distributed to their respective nodes. Applications can look up those objects from any server in the cell. EJB homes are also bound in the java:global namespace with names of the form...

    java:global/appName/moduleName/beanName

...but only in servers in which the enterprise beans run. However, java:global lookups on any EJB can be resolved from any server in the cell.


Related

Naming
Configured name bindings
Configuration documents
Use naming
Lookup names support in deployment descriptors and thin clients
Initial context support

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