Virtual Machine Providers
=========================

Cloudmesh is based on the concept of providers that make it possible to develop
API interfaces for different services independently while inheriting the
functionality form a common abstract class.


Let us demonstrate the concept of abstract providers for compute
providers. We assume that the source directories are stored in ~/cm.
We have the following structure::

    ~/cm/cloudmesh-abstract/cloudmesh/abstract/ComputeNodeABC.py
    ~/cm/cloudmesh-cloud/cloudmesh/vm/Provider.py

    ~/cm/cloudmesh-openstack/cloudmesh/openstack/compute/Provider.py
    ~/cm/cloudmesh-aws/cloudmesh/aws/compute/Provider.py
    ~/cm/cloudmesh-aws/cloudmesh/azure/compute/Provider.py
    ~/cm/cloudmesh-aws/cloudmesh/oracle/compute/Provider.py
    ~/cm/cloudmesh-aws/cloudmesh/google/compute/Provider.py
            ...

Here the ABC class determines which methods must be implemented by the
main cloud provider. This provider then detects the activity to the
cloud provider that is determined by the internal cloudmesh `cloud`
variable. To simplify authentication, the credentials can be stored in
the cloudmesh.yaml file.


Example: The yaml file ~/.cloudmesh/cludmesh.yaml contains the entry::

    cloudmesh:
      compute: # currently called cloud
        mycloud:
          cm:
            name: maycloud
            kind: aws
          credentials:
            ...
          defaults:
            size: ...
            image: ...

Now when we call::

    provider = cloudmesh.compute.Provider(service="mycloud")


The Provider will load in the provider from the AWS directory, as the cm.kind
is specified as `aws`. Thus the main provider delegates the tasks to interface
with the particular cloud type via the definitions coming from the cloudmesh
YAML file. This makes it possible to easily create multiple interfaces to
different cloud service providers while managing a uniform interface via the
ABC class. All providers in this hierarchy must inherit from the ABC class.

Deatils of a virtual machine provider
~~~~~~~~~~~~~~~---------------~~~~~~~

Here we list in more details how a virtual machine provider can look like::

    ~/cm/

        cloudmesh-compute/  #curertly named cloudmes-cloud
            cloudmesh/compute
                ComputeABC.py
                Provider.py
                command/vm.py
                command/image.py
                command/flavor.py

        cloudmesh-aws/
            cloudmesh/
                aws/Provider.py

        cloudmesh-azure/
            cloudmesh/
                azure/Provider.py

In this case, we have includes in the compute provider imports for the providers
defined in their own repositories. As we use the shared namespace they can be
accessed from the main provider easily. This allows us to simply add the
provider with a simple pip install::

    cd ~/cm/cloudmesh-compute/
    pip install .
    cd ~/cm/cloudmesh-aws/
    pip install .
    cd ~/cm/cloudmesh-azure/
    pip install .

Now the aws and azure providers are accessible in cloudmesh and if a command is
provided they can be accessed from there.