Spring-based Server Chassis

The Server Chassis provides the base server framework to host the Open Metadata and Governance (OMAG) Servers in the OMAG Server Platform.

The server-chassis-spring module is an implementation of the server chassis written using Spring Boot. Its main() method is located in a Java class called OMAGServerPlatform.

When the OMAGServerPlatform is first started, all of its REST APIs are visible and callable by an external client. However, only the Administration Services and Platform Services are operational at this point. The other Open Metadata and Governance (OMAG) services will each give an error response if called.

The OMAG Subsystems supporting the other OMAG services are selectively activated in one or more OMAG Servers that run in the OMAGServerPlatform. You can use the administration service to define and configure the subsystems for an OMAG Server. This definition is then stored in a configuration document for the server. This is a one-time activity.

Details of how to set up the configuration document, and activate/deactivate the open metadata services can be found in the OMAG Server Configuration User Guide.

Once the configuration document is in place it is possible to activate and deactivate the server in the OMAGServerPlatform many times over multiple platform restarts.

A detailed description of the internals of the OMAGServerPlatform during server start up is available here.

Application properties

Since this is a Spring Boot application, OMAGServerPlatform can be customized using the application.properties file found in the resources directory and using environment variables.

For example, OMAG servers can be automatically activated at startup by setting spring-boot property startup.server.list, typically in the application.properties file. The server names are listed without quotes. For example:

startup.server.list=cocoMDS1, cocoMDS2

Each server is started with the administration user id set in the spring-boot property startup.user.

For example:

startup.user=garygeeke

By default, this user id is set to the user id system.

When the platform shuts down, if any of the servers that were in the startup list are still running, they will be shut down before the server completes.

If startup.server.list is null then no servers are automatically started or stopped.

startup.server.list=

Adding a new subsystem to the OMAGServerPlatform

When the OMAGServerPlatform class is called, Spring Boot does a component scan for all Spring services that are in Java packages stemming from org.odpi.openmetadata.* and that are visible to this module.

To make a new Java package visible to OMAGServerPlatform, add its spring package to the pom.xml file for server-chassis-spring and it will be picked up in the component scan.

For example, this is the snippet of XML in the pom.xml file that adds the Asset Owner OMAS services to the OMAG server platform.

<dependency>
    <groupId>org.odpi.egeria</groupId>
    <artifactId>asset-owner-spring</artifactId>
</dependency>

Swagger

Swagger API documentation is generated with the chassis and is documented in Swagger Generation.

Spring Boot Actuator

Spring Boot Actuator is used to expose operational information about the running application such as health, metrics, info, dump. It uses HTTP endpoints or JMX beans to enable us to interact with it.

A “discovery page” is added with links to all the endpoints. The “discovery page” is available on /actuator by default. Once this dependency is on the class-path /info and /health endpoints are available out of the box.

In order to expose all endpoints over HTTP, use the following property:

management.endpoints.web.exposure.inlude=*

The exclude property lists the IDs of the endpoints that should not be exposed. For example, to expose everything over HTTP except the env and beans endpoints, use the following properties:

management.endpoints.web.exposure.include=*
management.endpoints.web.exposure.exclude=env,beans

The exclude property takes precedence over the include property.


License: CC BY 4.0, Copyright Contributors to the ODPi Egeria project.