WS-PGRADE/gUSE and Clouds - Science Gateways for Distributed Computing Infrastructures - page 101

user. Thus, the user has a clear view on how much the workflow did cost, and
which jobs were dominant in the workflow cost.

7.4.2 Execution of Cloud-Directed Jobs

After the workflow con guration is saved, the execution of the workflow is man-

aged by the workflow interpreter (WFI) and the DCI Bridge. These two components
also had to be modi ed to enable cloud-based job execution:

WFI: the workflow interpreter parses the workflow guration and prepares

the JSDL [OGSA-BES] that is submitted to the DCI Bridge. This part of the
WFI had to be extended by adding the CloudBroker-speci

' s con

￿

c parts to the JSDL

document.

DCI Bridge: this component had to be extended with a CBP plugin that is
capable of performing job submission and management with the CBP by using
the Java API of CBP. The DCI Bridge fetches authentication data from WS-
PGRADE as set in the authentication portlet.

￿

7.4.2.1 Modifications of the Workflow Interpreter (WFI) to Support
CBP Integration

The WFI is responsible for scheduling submission of jobs to different DCIs after
evaluating job status changes received from the DCI Bridge. For this, the WFI uses
the XML description of the workflow and available job instance information. Once
the WFI realizes that a job can be executed, it takes the job

' s description from the

workflow XML, collects the access information of input files belonging to the job,

creates the JSDL document describing the job, and finally submits the job to the

DCI Bridge. In the case of jobs set to run on a CBP service, the WFI simply maps
the XML attributes specifying the application, resource, region and instance to the
ones used in the JSDL.

7.4.2.2 Extensions of DCI Bridge

The DCI Bridge has been extended with a CBP plugin that is responsible for
communicating with CBP services. Not only one, but also a number of CBP ser-
vices can be con gured in the DCI Bridge. These services are identi ed by a name

and each has its own con guration, but all of them rely on the CBP plugin to

communicate with the target service.
DCI Bridge has two aspects: a con guration aspect and a job execution aspect.

In the con guration aspect administrators may enable the different plugins and set

their con guration, whereas in the job execution aspect the DCI Bridge accepts job