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Thomas Spatzier <thomas.spatzier at de.ibm.com> wrote on 10/21/2013 08:29:47
AM:

> you mentioned an example in your original post, but I did not find it.
Can
> you add the example?

Hi Thomas,

Here is the example I used earlier:

For example, consider
a two VM app, with VMs vmA, vmB, and a set of software components (ai's and
bi's)
to be installed on them:

vmA = base-vmA + a1 + a2 + a3
vmB = base-vmB + b1 + b2 + b3

let us say that software component b1 of vmB, requires a config value
produced by
software component a1 of vmA. How to declaratively model this dependence?
Clearly,
modeling a dependence between just base-vmA and base-vmB is not enough.
However,
defining a dependence between the whole of vmA and vmB is too coarse. It
would be ideal
to be able to define a dependence at the granularity of software
components, i.e.,
vmB.b1 depends on vmA.a1. Of course, it would also be good to capture what
value
is passed between vmB.b1 and vmA.a1, so that the communication can be
facilitated
by the orchestration engine.


Thanks,
LN

>
> Lakshminaraya Renganarayana <lrengan at us.ibm.com> wrote on 18.10.2013
> 20:57:43:
> > From: Lakshminaraya Renganarayana <lrengan at us.ibm.com>
> > To: OpenStack Development Mailing List
> <openstack-dev at lists.openstack.org>,
> > Date: 18.10.2013 21:01
> > Subject: Re: [openstack-dev] [Heat] A prototype for cross-vm
> > synchronization and communication
> >
> > Just wanted to add a couple of clarifications:
> >
> > 1. the cross-vm dependences are captured via the read/writes of
> > attributes in resources and in software components (described in
> > metadata sections).
> >
> > 2. these dependences are then realized via blocking-reads and writes
> > to zookeeper, which realizes the cross-vm synchronization and
> > communication of values between the resources.
> >
> > Thanks,
> > LN
> >
> >
> > Lakshminaraya Renganarayana/Watson/IBM at IBMUS wrote on 10/18/2013
02:45:01
> PM:
> >
> > > From: Lakshminaraya Renganarayana/Watson/IBM at IBMUS
> > > To: OpenStack Development Mailing List
> <openstack-dev at lists.openstack.org>
> > > Date: 10/18/2013 02:48 PM
> > > Subject: [openstack-dev] [Heat] A prototype for cross-vm
> > > synchronization and communication
> > >
> > > Hi,
> > >
> > > In the last Openstack Heat meeting there was good interest in
> > > proposals for cross-vm synchronization and communication and I had
> > > mentioned the prototype I have built. I had also promised that I
> > > will post an outline of the prototype ... Here it is. I might have
> > > missed some details, please feel free to ask / comment and I would
> > > be happy to explain more.
> > > ---
> > > Goal of the prototype: Enable cross-vm synchronization and
> > > communication using high-level declarative description (no wait-
> > > conditions) Use chef as the CM tool.
> > >
> > > Design rationale / choices of the prototype (note that these were
> > > made just for the prototype and I am not proposing them to be the
> > > choices for Heat/HOT):
> > >
> > > D1: No new construct in Heat template
> > > => use metadata sections
> > > D2: No extensions to core Heat engine
> > > => use a pre-processor that will produce a Heat template that the
> > > standard Heat engine can consume
> > > D3: Do not require chef recipes to be modified
> > > => use a convention of accessing inputs/outputs from chef node[][]
> > > => use ruby meta-programming to intercept reads/writes to node[][]
> > > forward values
> > > D4: Use a standard distributed coordinator (don't reinvent)
> > > => use zookeeper as a coordinator and as a global data space for
> > communciation
> > >
> > > Overall, the flow is the following:
> > > 1. User specifies a Heat template with details about software config
> > > and dependences in the metadata section of resources (see step S1
> below).
> > > 2. A pre-processor consumes this augmented heat template and
> > > produces another heat template with user-data sections with cloud-
> > > init scripts and also sets up a zookeeper instance with enough
> > > information to coordinate between the resources at runtime to
> > > realize the dependences and synchronization (see step S2)
> > > 3. The generated heat template is fed into standard heat engine to
> > > deploy. After the VMs are created the cloud-init script kicks in.
> > > The cloud init script installs chef solo and then starts the
> > > execution of the roles specified in the metadata section. During
> > > this execution of the recipes the coordination is realized (see
> > > steps S2 and S3 below).
> > >
> > > Implementation scheme:
> > > S1. Use metadata section of each resource to describe  (see
> > attached example)
> > > - a list of roles
> > > - inputs to and outputs from each role and their mapping to resource
> > > attrs (any attr)
> > > - convention: these inputs/outputs will be through chef node attrs
node
> [][]
> > >
> > > S2. Dependence analysis and cloud init script generation
> > >
> > > Dependence analysis:
> > > - resolve every reference that can be statically resolved using
> > > Heat's fucntions (this step just uses Heat's current dependence
> > > analysis -- Thanks to Zane Bitter for helping me understand this)
> > > - flag all unresolved references as values resolved at run-time at
> > > communicated via the coordinator
> > >
> > > Use cloud-init in user-data sections:
> > > - automatically generate a script that would bootstrap chef and will
> > > run the roles/recipes in the order specified in the metadata section
> > > - generate dependence info for zookeeper to coordinate at runtime
> > >
> > > S3. Coordinate synchronization and communication at run-time
> > > - intercept reads and writes to node[][]
> > > - if it is a remote read, get it from Zookeeper
> > > - execution will block till the value is available
> > > - if write is for a value required by a remote resource, write the
> > > value to Zookeeper
> > >
> > > The prototype is implemented in Python and Ruby is used for chef
> > > interception.
> > >
> > > There are alternatives for many of the choices I have made for
> theprototype:
> > > - zookeeper can be replaced with any other service that provides a
> > > data space and distributed coordination
> > > - chef can be replaced by any other CM tool (a little bit of design
> > > / convention needed for other CM tools because of the interception
> > > used in the prototype to catch reads/writes to node[][])
> > > - the whole dependence analysis can be integrated into the Heat's
> > > dependence analyzer
> > > - the component construct proposed recently (by Steve Baker) for
> > > HOT/Heat can be used to specify much of what is specified using the
> > > metadata sections in this prototype.
> > >
> > > I am interested in using my experience with this prototype to
> > > contribute to HOT/Heat's cross-vm synchronization and communication
> > > design and code.  I look forward to your comments.
> > >
> > > Thanks,
> > > LN_______________________________________________
> > > OpenStack-dev mailing list
> > > OpenStack-dev at lists.openstack.org
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>
>
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