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Apache Karaf Minho

Apache Karaf Minho is an application runtime, able to operate different kind of applications using application manager services.

It provides extensible launchers per application kind and out of the box services that any application running on Minho can leverage without cost.

Apache Karaf Minho is composed by:

  • Minho boot (Minho) bootstraps the runtimes for your applications, the runtimes are discovered and extensible
  • an API to interact with the boot if you need
  • profiles to easily add cross runtimes dependencies
  • services to easily add cross runtimes features (log, configurations, URL handlers, ...)
  • boot applications

Minho boot can be described/configure programmatically or by a provided JSON file.

Minho Boot

Minho boot is the main runtime orchestrator. It basically loads Minho Services via SPI, and it's configured via Config.

Config can be provided programmatically:

Config config = new Config();
...
Minho minho = Minho.build(config);
minho.init();
minho.start();

or loaded from an external resource like minho.json:

{
 "properties": {
    "foo": "bar"
 },
 "applications": [
    {
        "url": "/path/to/my/jar"
    }
 ]
}

Minho Boot is looking for minho.json file (aka Minho Config):

  • as system property: -Dminho.config=/path/to/minho.json
  • as environment variable: export MINHO_CONFIG=/path/to/minho.json
  • in the current classpath

Minho Services

A Minho Service is a class implementing the org.apache.karaf.minho.boot.spi.Service interface, and loaded via META-INF/services/org.apache.karaf.minho.boot.spi.Service, containing the FQDN of the implementation class.

The service doesn't have to implement any method by default. Optionally, you can define the following methods:

public class MyService implements org.apache.karaf.minho.boot.spi.Service {
    
    @Override
    public String name() {
        // return the service name
        return "my-service";
    }
    
    @Override
    public void onRegister(ServiceRegistry serviceRegistry) throws Exception {
        // callback method, called when the service is registered in the Minho Service Registry
        // you can interact with the Minho Service Registry `serviceRegistry` here, looking for services, etc
    }
    
    @Override
    public int priority() {
        // return the service priority, default is 1000. Lower priority are started before higher priority.
        return 1001;
    }
    
}

Runtime

Minho Boot provides a runtime with:

  • a launcher
  • a service registry (ServiceRegistry) where all services will be located
  • a config service (ConfigService) loads Minho config
  • a lifecycle service (LifeCycleService) is responsible to callback start and stop methods from the services

Then, org.apache.karaf.minho.boot.Karaf launcher can start (Minho.builder().build().start()) all Minho services located in the classloader, you can repackage all dependencies (jar) in a single uber jar.

Minho itself provides several "additional" services:

  • classpath: protocol handler
  • archive extractor
  • JSON configuration loader
  • Properties configuration loader
  • welcome banner
  • a much more! (take a look on the documentation for details)

Application manager services can also deploy "third party" applications, for instance:

  • OSGi application manager is able to deploy OSGi applications (bundles, Karaf 4 features)
  • Spring Boot application manager is able to deploy Spring Boot applications

Minho Services can be configured via the properties, using the service name as prefix.

You can configure launcher in minho.json:

    "properties": {
        "osgi.storageDirectory": "/path/to/storage",
        "spring-boot.cache": "/path/to/cache
    },

Each service is responsible to retrieve the Config service from the service registry, and get the properties.

Third party applications

When you use a third party application manager service, you can define the applications you want to deploy via Config service.

For instance, you can use the following minho.json configuration file:

{
  "properties": {
    "osgi.storageDirectory": "path/to/store",
    "osgi.cache": "path/to/cache"
  },
  "applications": [
    {
      "url": "https://repo1.maven.org/maven2/commons-lang/commons-lang/2.6/commons-lang-2.6.jar",
      "type": "osgi"
    }
  ]
}

Here, you can see how to configure and deploy commons-lang-2.6.jar in the OSGi application manager.

Run

You can use Apache Karaf Minho in your code, simply bootstrapping it and running with:

Minho minho = Minho.build(config);
minho.init();
minho.start();

or simply run with a minho.json:

$ java -jar minho.jar -Dminho.config=minho.json

Minho is launching all you describe in the minho.json.