Information Technology Reference
In-Depth Information
To increase reusability, the logic of the system is implemented with set of
workflows and modules (the codes that implement the executables invoked by each
node). Modules are self-contained Java modules or scripts that act as interfaces to
resources that are external to HELIOGate. They can be invoked either directly by
the advanced propagation model portlet as atomic operations, or as a result of the
execution of a node in a workflow. Modules act as interfaces to external web
services. Among the external web services developed by the HELIO, AMDA and
VSO projects, the most relevant to HELIOGate are the HELIO event catalogue
(HEC) that catalogues solar events, the HELIO feature catalogue (HFC) that cat-
alogues solar features, AMDA to evaluate data series, the Instrument Capabilities
Service (ICS) and the instrument location service (ILS) that catalogue information
on the instruments catalogues across the Solar System. These external web services
expose SOAP and REST interfaces and return VO-TABLES as results of queries.
Small modules are also used to control the SHEBA propagation model and the data
processing scripts de
ned by the users. The SHEBA propagation model is written
in IDL7.1 (IDL 2014) language, and it relies on the SSW libraries developed by
NASA (SSW 2014).
For users who do not want to develop workflows in non-native languages such
as TAVERNA, the DCI bridge of the HELIOGate frontend can connect to the
SHIWA interoperability platform through the GEMLCA service. Up to now,
external workflows have been developed using the TAVERNA language, and they
connect to web services using SOAP interfaces.
The hardware architecture is comprised of a set of front-end machines and a
back-end composed of a cluster and storage. Three instance of HELIOGate (pro-
duction, development and testing) run in XEN virtual images hosted on a Dell 2950
with 16 GB of RAM and a 80 GB hard disk. The gateway instances are connected
to the computational and storage facility of the Computer Architecture Group of
Trinity College Dublin that comprises a 216-core Torque cluster composed of 16
worker nodes (Dell R410) and up to 80 TB of storage. As typical user jobs rely on
large volumes of local data, this data is exported to all nodes in the cluster using
many automounted NFS shares.
14.7 User Experience
The experiences gathered during the development, maintenance, and usage of
HELIOGate have highlighted some of the characteristics of the WS-PGRADE and
gUSE technologies: mainly the flexibility and the broad spectrum of the solutions
that can be implemented within this framework. Actually, the suite of technologies
offered by SCI-BUS support the development of workflow-oriented gateways
offering flexibility and customization along three main dimensions: infrastructure,
design of application, and their access and execution.
Regarding infrastructures, it is worth noting that the SCI-BUS technologies
can connect into a large variety of DCIs that range from clusters to grids to clouds.
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