Information Technology Reference
In-Depth Information
in the network. On top, the
platform layer
supports application related man-
agement tasks including e.g. the deployment of application artifacts to different
nodes as well as starting and stopping components. Finally, the
application layer
facilitates the application development by providing APIs and debugging tools.
3.1 Daemon Layer
The daemon layer (cf. Fig. 2) consists of different nodes on which a
daemon plat-
form
is running in the background. The daemon platform represents the entry
point for a node to the cloud. It has the purpose of facilitating the discovery of
the underlying node, which can only be part of the cloud when announced by the
awareness agent (
awa
). Depending on the type of network the cloud should span,
different announcement protocols have to be used. In case of a local area net-
work, a simple TCP/IP multicast mechanism is su
cient in many cases, whereas
more complex network setups also require more elaborated announcement meth-
ods.
3
Furthermore, the daemon agent (
dae
) provides a high-level service API for
application management from the platform layer. This API allows for starting
and stopping application platforms, on which application components (
App
)
can be executed. The design is meant to enforce a strict separation between
daemon and application execution in order to ensure long-lived manageability
of the node even if an application is erroneous. During application execution
the daemon can monitor the application platforms and terminate them when-
ever appropriate. The daemon platform also has access to repositories containing
software bundles. Currently the repository is based on flat files, but the idea is
to use a chain of Maven repositories to support versioning, etc. In this context
it is distinguished between local, private and public repositories. A local reposi-
tory is located directly on the node of the daemon, whereas a private repository
is typically owned by an organization and shared by the member nodes of this
organization. Public repositories have global scope and are thus available on In-
ternet scale. The daemon uses these repositories for updating itself by regularly
testing if new versions of its library are available.
In the following the role of the daemon layer is illustrated with respect to
the running example of the Mandelbrot application. When a user wishes to de-
ploy the Mandelbrot application on, e.g., a pool of workstation computers she
has to make sure that all nodes can be discovered by the cloud infrastructure.
Therefore, the minimal daemon platform has to be installed on each node. The
platform registers itself e.g. as a unix daemon or windows service, such that it
is started each time the host operating system is started. Therefore, the dae-
mon has to be installed only once and needs no further attention afterwards.
When assuming that the daemon is already present at each of the nodes, e.g. as
part of a customized system distribution used for each pool workstation, then
no administration tasks are required in the daemon layer for the Mandelbrot
application.
3
In ongoing work Internet scale announcement and discovery is analyzed by utilizing
existing peer-to-peer mechasims based on registries and superpeers.
