Common Libraries Specification

The core facilities of the e-Infrastructure include a set of Java libraries that compose into solutions for managing software and hardware as resources of the e-Infrastructure, as well as for interacting with those resources. This document overviews these common libraries.

Overview

Common libraries are grouped in three main distributions:

• the Featherweight Stack (FWS) is the client stack of the e-Infrastructure, i.e. the set of libraries that allow clients to interact with services that are managed by the e-Infrastructure, first and foremost the services of its enabling technologies. It is the client stack o

The featherweight nature of the stack is in the footprint of its components, which is very small in terms of code, dependencies, and overall usage requirements. Overall, the FWS simplifies the task of clients that wish to interact with the services managed by the e-Infrastructure, thereby encouraging uptake.

• Smartgears is a set of libraries that transform services and service containers into resources managed by the e-Infrastructure. Most noticeably, SmartGears meets the description, publication, lifecycle management, and controlled sharing requirements which characterise hardware and software as resources of the e-Infrastructure.

SmartGears delivers these management functions in a standard manner, i.e relying only on Servlet specifications, and transparently, i.e. without demanding source-level dependencies from applications. Overall, SmartGears brings a wide range of software under the management regime of the e-Infrastructure, without requiring dedicated development. Equally, it allows the enabling technologies underneath the e-Infrastructure to evolve along standard pathways.

• the gCore Application Framework is a comprehensive framework to develop services as resources of the e-Infrastructure, i.e. software written to run and be managed in the infrastructure.

gCore offers maximum integration between software and e-Infrastructure, trading off simplicity for flexibility in development. The trade-off is most advantageous for the services that enable the e-Infrastructure, and indeed gCore is the basis upon which the vast majority of those services are built. As a classic development framework, gCore is less indicated as a resource enabler of existing software, a role which is fulfilled by SmartGears transparently.

Key features

Collectively, the common libraries provide for:

transparent publication and lifecycle management

perodic and event-based publication of resource profiles from initial configuration;

state transitions in response to internal or external events;

transparent sharing

scope assignment, removal, and validation for hardware and software resources;

scope validation for incoming calls;

scoping of outgoing calls;

transparent security management

authentication and authorisation of calls to software resources.

resource discovery

automatic assignment and handling of unrecoverable, retry-same, and retry-equivalent failure semantics;

state management support for software resource development

WSRF-compliant support for access, persistence, publication, and discovery of stateful instances;

resource publication and discovery support for software resource development

high-level models of resources, queries and query results;

resource encryption and decryption for publication and querying;

remote interaction support for software resource development

high-level model of service calls

best-effort strategies for service replica discovery and replica management;

caching;

plugin management support for software resource development

transparent plugin discovery, registration, unregistration;

Design

Philosophy

The system delivers its library support for resource management and software resource development in two distinct forms.

In the first form, it provides a single a single application framework (the gCube Application Framework) which is tightly integrated with a particular set of runtime technologies (Globus’ WS-Core Container). Framework and runtime are bundled in a single distribution (gCore) which can be installed on hardware resources to bring them under the management regime of the system. The framework includes a set of programming abstractions that simplify significantly the development of software resources which can again be brought under the management regime of the system.

In the second form, the system provides a set of libraries that specialise in different management and development support functions. The libraries that support resource management functions are independent of runtime technologies and raise no compile-time or run-time dependencies on the managed resources. The libraries that support development of software resources do so in a modular fashion, which allows partial and on-demand dependencies on system facilities.

The transparencies granted by the first approach have been instrumental to the rapid and consistent growth of the system, reducing significantly administration and development costs for hardware and software resources explicitly allocated to the system or developed for it. The commitment to lightweight integration mechanisms and design modularity of the second approach aligns with modern practices and brings a wider range of resources under the management regime of the system.

Architecture

The core facilities of the system rely on the following libraries:

• gcf: the gCube Application Framework, a one-stop solution for resource management support and software resource development support;

• ghn-service: a system component that transparently manages HTTP services that run in a Servlet container;

• ghn-client: an extensible framework for system components that transparently manage clients of HTTP services;

• ghn-client-proxy: a system component that transparently manages client calls to HTTP services;

• common-clients: an API for client library development;

• common-gcore-clients: an extension of the common-clients API for clients of gCore services;

• common-scope: scope handling facilities;

• common-resources: an implementation of the resource model;

• common-resources-publisher: local API of remote publication services;

• common-resources-discovery: local API of remote discovery services;

• common-utils-encryption: resource encryption/decryption facilities;

Deployment

Common Libraries are a set of facilities available as Java libraries. Therefore, there is no deployment scheme for them. They are just individually and independently co-deployed with components that need to use a particular feature that one of the offers.