Connecting applications to a service integration bus

The factors that affect how applications connect to a service integration bus so that they can use resources provided by that bus.

To connect to a service integration bus, an application actually connects to a messaging engine on the bus.

In the simplest case, you can configure the environment to automatically connect applications to any available messaging engine on the bus. You can specify extra configuration details to control the connection process; for example, to identify special bootstrap servers, or to limit connection to a subgroup of available messaging engines.

In the case of JMS, the information that controls the connection process is configured on a JMS connection factory.

Applications running in an application server

Applications that are running inside an application server can locate a suitable messaging engine themselves.

If the messaging engine is found in the same server, a connection is created that provides the application with the fastest available connection to a messaging engine. Otherwise, if a messaging engine is found in another process - on the same or a different host - a remote connection is made. If no suitable messaging engine is found the application fails to connect to the bus.

Figure 1. Connection to an messaging engine - Applications running in an application server hostA and hostB are shown. hostA contains two application servers: server1 on hostA contains Application Y; server 3 on hostA contains Application X connected to a local messaging engine; . hostB contains server2, which also contains a messaging engine. server1 and server2 are members of the same bus, and application Y on hostA/server1 is connected to the messaging engine running on hostB/server2.

hostA and hostB are shown. hostA contains two application servers: server1 on hostA contains Application Y; server 3 on hostA contains Application X connected to a local messaging engine; . hostB contains server2, which also contains a messaging engine. server1 and server2 are members of the same bus, and application Y on hostA/server1 is connected to the messaging engine running on hostB/server2.

The figure shows two applications running in application servers. Application X on server3 has connected to the messaging engine running in the same server. Application Y on server1 has connected to a messaging engine that is running in the same bus but on a different server and host, because server1 does not have a suitable messaging engine.

Applications running outside an application server

Client applications running outside an application server (for example, running in a client container or outside the WebSphere environment) cannot locate a suitable messaging engine themselves and must complete a bootstrap process through a bootstrap server. A bootstrap server is an application server that is running the SIBService service, but is not necessarily running any messaging engines. The bootstrap server selects a messaging engine that is running in an application server that supports the desired target transport chain.

Figure 2. Connection to a messaging engine - Applications running outside an application server hostA and hostB are shown. hostA contains server1, which is a bootstrap server. hostB contains server2, which contains a messaging engine. server1 and server2 are members of the same bus. Application X is a client application running outside an application server. This application has a bootstrap connection to server1, and a connection to the messaging engine running in server2.

hostA and hostB are shown. hostA contains server1, which is a bootstrap server. hostB contains server2, which contains a messaging engine. server1 and server2 are members of the same bus. Application X is a client application running outside an application server. This application has a bootstrap connection to server1, and a connection to the messaging engine running in server2.

This figure shows a client application running outside an application server. To connect to a messaging engine, the application connects first to a bootstrap server. The bootstrap server selects a messaging engine then tells the client application to connect to that messaging engine.

A bootstrap server uses a specific port and bootstrap transport chain, which with the host name form the endpoint address of the bootstrap server.

The properties of a JMS connection factory used by a client application control the selection of a suitable messaging engine and how the client connects to the selected messaging engine. By default, a connection factory tries to use a bootstrap server that has an endpoint address of localhost:7276:BootstrapBasicMessaging. That is, the client application tries to use a bootstrap server on the same host as the client, and using port 7276 and the predefined bootstrap transport chain called BootstrapBasicMessaging.

Note:

For the i5/OS platform, you must (at least) change the default endpoint address from localhost:7276:BootstrapBasicMessaging to your.server.name:7276:BootstrapBasicMessaging.

When you create an application server, it is automatically assigned a unique non-secure bootstrap port, SIB_ENDPOINT_ADDRESS, and a secure bootstrap port, SIB_ENDPOINT_SECURE_ADDRESS. If you want to use an application server as a bootstrap server, and the server has been assigned a non-secure port other than 7276, or you want to use the secure port, then you need to specify the endpoint address of the server on the Provider endpoints property of the connection factory.

The endpoint addresses for bootstrap servers must be specified in every connection factory that is used by applications outside of an application server. To avoid having to specify a long list of bootstrap servers, you can provide a few highly-available servers as dedicated bootstrap servers. Then you only need to specify a short list of bootstrap servers on each connection factory.

The messaging engine selection process

The selection process is used to choose a messaging engine that an application should connect to so that it can use the resources of a service integration bus. The information that controls the selection process is configured on the connection factory (or programmatically by the application). The information is used to find the most suitable messaging engine in the bus for the application to connect to. You can configure the properties of the connection factory to restrict the range of messaging engines that applications can connect to.

The default configuration enables applications to connect to any available messaging engine in the bus. For this configuration, you only need to specify the one required connection property, Bus name, which sets the name of the bus to which the application wants to connect.

Although a connection can be made to any available messaging engine, the connection process applies a few simple rules to find the most suitable messaging engine. For an application running in an application server, the process is as follows:

The process looks for a messaging engine in the required bus within the same application server. If a messaging engine in the required bus is found in the same application server then a connection is made from the application to the messaging engine. If a suitable messaging engine is not found, the next rule is checked.
The process looks for a messaging engine that is running on the same host as the application. If a messaging engine is found running on that host, then the application makes a remote connection to the selected messaging engine. If a suitable messaging engine is not found, the next rule is checked.
The process looks for a messaging engine anywhere in the bus. If a suitable messaging engine is found the application makes a remote connection to the selected messaging engine. If a suitable messaging engine is not found, the connection attempt fails.

For an application running outside an application server, connection requests are workload balanced across all the available messaging engines in the bus.

In both cases (that is, an application running in an application server and an application running outside an application server) you can restrict the range of messaging engines available for connection, to a subgroup of those available in the service integration bus. You do this by configuring the following connection properties of the connection factory:

Target inbound transport chain

The messaging engine inbound transport chain that must be supported by the application server in which the messaging engine runs.

These transport chains specify the communication protocols that can be used to communicate with the application server that the client application is connected to. The following predefined messaging engine inbound transport chains are provided:

InboundBasicMessaging: JFAP over TCP/IP
InboundSecureMessaging: JFAP over SSL over TCP/IP

Connection proximity

For an application running in an application server, this property defines the proximity of messaging engines relative to the application server. For an application running outside an application server, this property defines the proximity of messaging engines relative to the bootstrap server.

Bus: Connections can be made to messaging engines in the same bus.
A suitable messaging engine in the same server is selected ahead of a suitable messaging engine in the same host, and in turn ahead of a suitable messaging engine in another host.
Cluster: Connections can be made to messaging engines in the same server cluster. If the application is not running in a clustered server, or the bootstrap server is not in a cluster, then there are no suitable messaging engines.
A suitable messaging engine in the same server is selected ahead of a suitable messaging engine in the same host, and in turn ahead of a suitable messaging engine in another host.
Host: Connections can be made to messaging engines in the same host. A suitable messaging engine in the same server is selected ahead of a suitable messaging engine in the same host.
Server: Connections can be made to messaging engines in the same application server.

Target group

The name of a target that resolves to a group of messaging engines on which the connection proximity check is applied to select a suitable messaging engine.

Before the connection proximity search is performed the set of messaging engines that are members of the specified target group are selected. The connection proximity search is then restricted to these messaging engines. If a target group is not specified (the default), then all messaging engines in the bus are considered during the connection proximity search.

For example, if the Target type property is set to Bus member name, the Target group specifies the name of the bus member from which suitable messaging engines can be chosen.

Target type

The type of target named in the Remote target group parameter; for example, if set to Bus member, the connection factory retrieves the active messaging engines in the named bus member.

Bus member name: The name of a bus member. This option retrieves the active messaging engines that are hosted by the named bus member (an application server or server cluster).
Custom messaging engine group name: The name of a custom group of messaging engines (that form a self-declaring cluster). This option retrieves the active messaging engines that have registered with the named custom group.
Messaging engine name: The name of a messaging engine. This option retrieves the available endpoints that can be used to reach the named messaging engine.

Target significance

This property defines whether or not the connection proximity search must be restricted to only the messaging engines in the target group.

Preferred: It is preferred that a messaging engine be selected from the target group. A messaging engine in the target group is selected if one is available. If a messaging engine is not available in the target group, a messaging engine outside the target group is selected if available in the same service integration bus.
Required: It is required that a messaging engine be selected from the target group. A messaging engine in the target group is selected if one is available. If a messaging engine is not available in the target group, the connection process fails.