Open Stack

An honest question,

U are mentioning what appears to be the basis for a full programming language (variables, calling other workflows - similar to functions) but then u mention this is being stuffed into yaml.

Why?

It appears like u might as well spend the effort and define a grammar and simplistic language that is not stuffed inside yaml. Shoving one into yaml syntax seems like it gets u none of the benefits of syntax checking, parsing, validation (highlighting...) and all the pain of yaml.

Something doesn't seem right about the approach of creating languages inside the yaml format (in a way it becomes like xsl, yet xsl at least has a spec and is well defined).

My 2 cents....

Sent from my really tiny device...

On Feb 14, 2014, at 7:22 PM, "Alexander Tivelkov" <ativelkov at mirantis.com<mailto:ativelkov at mirantis.com>> wrote:


Hi folks,


Murano matures, and we are getting more and more feedback from our early adopters. The overall reception is very positive, but at the same time there are some complaints as well. By now the most significant complaint is is hard to write workflows for application deployment and maintenance.

Current version of workflow definition markup really have some design drawbacks which limit its potential adoption. They are caused by the fact that it was never intended for use for Application Catalog use-cases.


I'll briefly touch these drawbacks first:

  1.  Murano's workflow engine is actually a state machine, however the workflow markup does not explicitly define the states and transitions.
  2.  There is no data isolation within any environment, which causes both potential security vulnerabilities and unpredictable workflow behaviours.
  3.  There is no easy way to reuse the workflows and their related procedures between several applications.
  4.  The markup uses JSONPath, which relies on Python’s 'eval' function. This is insecure and has to be avoided.
  5.  5. The workflow markup is XML-based, which is not a common practice in the OpenStack community.

So, it turns out that we have to design and implement a new workflow definition notation, which will not have any of the issues mentioned above.

At the same time, it should still allow to fully specify the configuration of any third-party Application, its dependencies with other Applications and define specific actions which are required for Application deployment, configuration and life cycle management.

This new notation should allow to do the following:


  *   List all the required configuration parameters and dependencies for a given application

  *   Validate user input and match it to the defined parameters

  *   Define specific deployment actions and their execution order

  *   Define behaviors to handle the events of changes in application’s environment


Also, it should satisfy the following requirements:


  *   Minimize the amount of configuration for common application parts, i.e. reuse existing configuration parts and add only difference specific to the application.

  *   Allow to use different deployment tools with using the same markup constructs. i.e. provide a high-level abstraction on the underlying tools (heat, shell, chef, puppet etc)

  *   For security reasons it should NOT allow to execute arbitrary operations - i.e. should allow to run only predefined set of meaningful configuration actions.



So, I would suggest to introduce a simple and domain specific notation which would satisfy these needs:

  *   Application dependencies and configuration properties are defined declaratively, in a way similar to how it is done in Heat templates.

  *   Each property has special constraints and rules, allowing to validate the input and applications relationship within the environment.

  *   The workflows are defined in imperative way: as a sequence of actions or method calls. This may include assigning data variables or calling the workflows of other applications.

  *   All of these may be packaged in a YAML format. The example may look something like this [1]


The final version may become a bit more complicated, but as the starting point this should look fine. I suggest to cover this in more details on our next IRC meeting on Tuesday.


Any feedback or suggestions are appreciated.



[1] https://etherpad.openstack.org/p/murano-new-dsl-example

--
Regards,
Alexander Tivelkov
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