Wednesday, August 22, 2018

OSGi Remote Services Between Python and Java

In a previous post, I described the support for OSGi Remote Services and Remote Service Admin in iPOPO 0.8.0 release.   The previous post refers to a tutorial showing a Python service impl and Python consumer.

Python<->Java Distribution Provider

Included with iPOPO 0.8.0 is a distribution provider that allows remote services between Java and Python frameworks.   For example, this is a tutorial, that uses Karaf on the Java side as the remote service implementation, and has a Python consumer that calls the Java-implemented remote service.

Python Service Implementation with Java Consumers

This distribution provider also supports Python-implemented remote services, with Java/OSGi consumers.   With iPOPO for dynamic service injection in Python, and Declarative Services for Java/OSGi, this allows very easy Python<->Java service-level interaction, with support for all dynamics, RSA management agent, extensible/customizable topology management, management of complicated service dependencies, pluggable local and network discovery, and other RS/RSA features handled consistently in both Java and Python.  As well, the use of OSGi-specified EndpointDescription service metadata allows service-level interoperability across languages.

Python<->Java with Protocol Buffers Serialization

Also included with this distribution provider is serialization using Google's protocol buffers.  This allows open, extensible, and efficient rpc between Python and Java.

Tuesday, August 21, 2018

Python for OSGi Remote Services

The iPOPO project is a Python implementation of key parts of a standard OSGi framework...e.g. bundles, the service registry and servicereference api, and a dynamic service injection framework similar to the Apache iPOJO project...thus the name iPOPO.

With the 0.8.0 release of iPOPO, there is now a Python implementation of the OSGi Remote Services and Remote Service Admin (RSA) specifications.   To distinguish from the previously-provided remote services in iPOPO, this is known as RSA Remote Services.

iPOPO's RSA Remote Services has many of the same advantages as Java-based Remote Services/RSA.  Some of these advantages:

Decoupling - name/service contract is decoupled from the implementation (and distribution)

Dynamics - The service registry dynamics behavior, along with all notifications, etc is available in Python

Injection and Service Dependency Management - iPOPO provides service injection and dependency management, built upon the Python API

Standard RemoteServiceAdmin Management Agent, RSA Console Commands

API for Distribution and Discovery Providers - There are documented APIs for creating new distribution and discovery providers, making it easy to support other transports and implementations for distribution (e.g. REST/JaxRS, Jsonrpc, MQTT, Zeroconf Discovery, etc).

Other advantages of Java-based OSGi services are described here.   All of these advantages apply to Python/iPOPO-based services, but Python can be used to implement and/or consume services.

Currently, there are two distribution providers included with iPOPO 0.8.0:  XmlRpc, Python-Java and one discovery provider: etcd.   See here for tutorials showing their usage with included sample remote services. 

Other distribution and discovery providers are being considered or worked on.  If you are interested in seeing a particular transport supported for distribution or discovery please open an issue on the iPOPO project.

Remote Services between Python and Java

The Python-Java distribution provider makes it possible to use OSGi Remote Services between Python and Java...on both sides.    This allows Remote Services to be exported from Python, and discovered/imported and consumed in Java, or exported from Java and discovered/imported/consumed from Python.  See here for a sample and tutorial.   These capabilities and the underlying distribution provider will be described in more detail in a subsequent posting.