Information Technology Reference
In-Depth Information
grid/cloud/service-based middleware. The separate DCIs can be handled by
plug-ins and their numbers can be increased without any restriction. Main com-
ponents of the DCI Bridge are:
BES Service
Job Registry
Proxy Cache
DCI Plugin Manager (Fig.
4.2
shows the gLite plugin manager as an example)
Job Temporary Directory (not shown in Fig.
4.2
to simplify the
gure).
The plugin manager is the main service of the DCI Bridge; it contains four types
of queues: Input Queue, Submit Queue, Status Queue (DCI and Job Status queues)
and Output Queue (DCI and Job Output queues). All of them are processed by
several threads that are created dynamically according to the load of the DCI
Bridge. The DCI Bridge administrator can de
ne the maximum number of queue-
handling threads. There are as many Plugin Manager instances as there are DCIs
connected to the given gateway. For example, if a gateway is connected to a gLite
and a BOINC grid, then it has two plugin manager instances.
The BES service of DCI Bridge accepts standardized JSDL job description
documents, which are based on well-de
ned XML schemes, and which contain
information about the job inputs, binaries, runtime settings, and output locations.
The core JSDL itself is not powerful enough to fit all needs, but various extensions
are used to overcome this issue. The DCI Bridge makes use of three legacy
extensions: one for de
ning execution resources, one for proxy service, and one for
callback service access. The execution resource extension is needed both for the
core DCI Bridge in order to de
c execution resource needs and for the
metabroker service. The proxy service extension is needed for security management
and credential handling (see below). The callback service extension is needed if
status change callback functionality is needed: the DCI Bridge will initiate a call to
the service speci
ne speci
ed in the extension upon every job status change.
Incoming BES jobs are placed in the job registry and their references are passed
to the other DCI Bridge services. The job
is reference is immediately placed into the
input queue of the corresponding Plugin Manager. The processing of a job consists
of the following steps:
'
Security management
Input
file management
Submission
Status inquiry
Transfer status information to gUSE workflow interpreter (WFI)
Output inquiry
Result
files upload to gUSE storage.
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