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Hi Alex,

Personally I like the approach and how you explain it. I just would like to
know your opinion on how this is better from someone write Heat template
that creates Active Directory  lets say with one primary and one secondary
controller and then publish it somewhere. Since Heat do supports software
configuration as of late and has concept of environments [1] that Steven
Hardy generously pointed out in another mailing thread that can be used for
composition as well it seems like everything you said can be done by Heat
alone

[1]:
http://hardysteven.blogspot.co.uk/2013/10/heat-providersenvironments-101-ive.html


On Mon, Feb 24, 2014 at 7:51 PM, Alexander Tivelkov
<ativelkov at mirantis.com>wrote:

> Sorry folks, I didn't put the proper image url. Here it is:
>
>
> https://creately.com/diagram/hrxk86gv2/kvbckU5hne8C0r0sofJDdtYgxc%3D
>
>
> --
> Regards,
> Alexander Tivelkov
>
>
> On Mon, Feb 24, 2014 at 7:39 PM, Alexander Tivelkov <
> ativelkov at mirantis.com> wrote:
>
>> Hi,
>>
>> I would like to initiate one more discussion about an approach we
>> selected to solve a particular problem in Murano.
>>
>> The problem statement is the following: We have multiple entities like
>> low level resources and high level application definitions. Each entity
>> does some specific actions for example to create a VM or deploy application
>> configuration. We want each entity's workflow code reusable in order to
>> simplify development for a new application as the current approach with XML
>> based rules requires significant efforts.
>>
>> After internal discussions inside Murano team we come up to the solution
>> which uses a well known programmatic concept - classes, their inheritance
>> and composition.
>>
>> In this thread I would like to share our ideas and discuss the
>> implementation details.
>>
>> We want to represent each and every entity being manipulated by Murano,
>> as an instance of some "class". These classes will define structure of the
>> entities and their behavior. Different entities may be combined together,
>> interacting with each other, forming a composite environment. The
>> inheritance may be used to extract common structure and functionality into
>> generic superclasses, while having their subclasses to define only their
>> specific attributes and actions.
>>
>> This approach is better to explain on some example. Let's consider the
>> Active Directory windows service. This is one of the currently present
>> Murano Applications, and its structure and deployment workflow is pretty
>> complex. Let's see how it may be simplified by using the proposed
>> object-oriented approach.
>>
>> First, let's just describe an Active Directory service in plain English.
>>
>> Active Directory service consists of several Controllers: exactly one
>> Primary Domain Controller and, optionally, several Secondary Domain
>> Controllers. Controllers (both primary and Secondary) are special Windows
>> Instances, having an active directory server role activated. Their specific
>> difference is in the configuration scripts which are executed on them after
>> the roles are activated. Also, Secondary Domain Controllers have an ability
>> to join to a domain, while Primary Domain Controller cannot do it.
>>
>> Windows Instances are regular machines having some limitations on the
>> their images (it should, obviously, be Windows image) and hardware flavor
>> (windows is usually demanding on resources). Also, windows machines may
>> have some specific operations, like configuring windows firewall rules or
>> defining local administrator password.
>>
>> And the machines in general (both Windows and any others) are simple
>> entities which know how to create virtual machines in OpenStack clouds.
>>
>> Now, let's map this model to object-oriented concept. We get the
>> following classes:
>>
>>
>>    1.
>>
>>    Instance. Defines common properties of virtual machines (flavor,
>>    image, hostname) and deployment workflow which executes a HEAT template to
>>    create an instance in the cloud.
>>    2.
>>
>>    WindowsInstance - inherits Instance. Defines local administrator
>>    account password and extends base deployment workflow to set this password
>>    and configure windows firewall - after the instance is deployed.
>>    3.
>>
>>    DomainMember - inherits Windows instance, defines a machine which can
>>    join an Active Directory. Adds a "join domain" workflow step
>>    4.
>>
>>    DomainController - inherits Windows instance, adds an "Install AD
>>    Role" workflow steps and extends the "Deploy" step to call it.
>>    5.
>>
>>    PrimaryController - inherits DomainContoller, adds a "Configure as
>>    Primary DC" workflow step and extends "Deploy" step to call it. Also adds a
>>    domainIpAddress property which is set during the deployment.
>>    6.
>>
>>    SecondaryController, inherits both DomainMember and DomainController.
>>    Adds a "Configure as Secondary DC" worflow step and extends Deploy() step
>>    to call it and the "join domain" step inherited from the "Domain Member"
>>    class.
>>    7.
>>
>>    ActiveDirectory -  a primary class which defines an Active Directory
>>    application. Defines properties for PrimaryController and
>>    SecondaryControllers and a "Deploy" workflow which call appropriate
>>    workflows on the controllers.
>>
>>
>> The simplified class diagram may look like this:
>>
>>
>>
>>
>>
>> So, this approach allows to decompose the AD deployment workflow into
>> simple isolated parts, explicitly manage the state and create reusable
>> entities (of course classes like Instance, WindowsInstance, DomainMember
>> may be used by other Murano Applications). For me this looks much, much
>> better than the current implicit state machine which we run based on XML
>> rules.
>>
>> What do you think about this approach, folks? Do you think it will be
>> easily understood by application developers? Will it be easy to write
>> workflows this way? Do you see any drawbacks here?
>>
>> Waiting for your feedback.
>>
>>
>> --
>> Regards,
>> Alexander Tivelkov
>>
>
>
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>


-- 
Sincerely yours
Stanislav (Stan) Lagun
Senior Developer
Mirantis
35b/3, Vorontsovskaya St.
Moscow, Russia
Skype: stanlagun
www.mirantis.com
slagun at mirantis.com
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