Information Technology Reference
In-Depth Information
is represented by the HTTP INTERFACE box in Fig.
5.3
. On upload or download,
the Blacktop is
first requested to create an alias (
createAlias
) for a remote
le
residing on some remote storage; later on, client
s read/write operations from/to the
HTTP alias URL are translated automatically to actual storage read/write operations
by the Blacktop. This technique is also known as HTTP tunneling. Aliases can be
created for reading or writing. An alias URL thus indeed behaves as an
'
“
alias
”
of
the remote resource.
Aliases can be created with an arbitrary
lifetime
. In this way, storage resources
can also be shared over HTTP for a longer time (days, weeks, or months), or can be
made accessible for other parties who are not aware of the particular storage
resource protocol (e.g., computing elements having HTTP capability only). Aliases
are managed and made persistent by the
Alias manager
component.
Different storages use different authentication mechanisms. The most frequent
authentication types are: username-password authentication (SFTP), access key
-
secret key (S3), X.509 proxy-based authentication (with or without VOMS
extension, used by GridFTP or SRM). Such authentication data are called cre-
dentials that need to be passed to the Blacktop service to be able to connect to the
related storage resources. Due to the session management of the Blacktop, these
credentials have to be passed in the very
first operation and are used as long as the
session does not expire.
When creating aliases, credentials that are needed to access a remote file or a
folder must be given to the Blacktop. These credentials will be used throughout the
whole lifecycle of the alias each time a request comes over the HTTP alias. Note
that clients using an alias (potentially different from the client who had created
them) are not required to be aware of the credentials needed to access the storage
resource.
5.3 Data Avenue in WS-PGRADE/gUSE
Data Avenue can be used in two levels in WS-PGRADE/gUSE. As mentioned
earlier, starting from the WS-PGRADE/gUSE release 3.6.0, Data Avenue UI is part
of the WS-PGRADE/gUSE portlet set. The Data Avenue UI portlet is available
through the menu item
“
Data Avenue
”
; portal users can thus manage remote storage
resources, upload or download
files within the WS-PGRADE/gUSE environment in
the same way as described in Sect.
5.2.1
, and as shown in Fig.
5.4
.
Beyond this feature, WS-PGRADE/gUSE also makes it possible to exploit
remote storage resources during workflow execution. This feature is described in
more detail in the following paragraphs.
When designing workflows, so-called
ports
can be created for jobs that allow one
to specify the inputs for individual computations, and to give name or location for
the outputs, respectively. There are numerous options for determining the
type
of
such ports. The
source
of an input port can be a local
file accessible
over HTTP, cloud, grid, etc., protocols; similarly, there are several options for
file or a remote
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