On 12/11/13 10:32 -0800, Clint Byrum wrote:
Excerpts from Thomas Spatzier's message of 2013-11-11 08:57:58 -0800:
Hi all,
I have just posted the following wiki page to reflect a refined proposal
for HOT software configuration based on discussions at the design summit
last week. Angus also put a sample up in an etherpad last week, but we did
not have enough time to go thru it in the design session. My write-up is
based on Angus' sample, actually a refinement, and on discussions we had in
breaks, plus it is trying to reflect all the good input from ML discussions
and Steve Baker's initial proposal.
https://wiki.openstack.org/wiki/Heat/Blueprints/hot-software-config-WIP
Please review and provide feedback.
Hi Thomas, thanks for spelling this out clearly.
I am still -1 on anything that specifies the place a configuration is
hosted inside the configuration definition itself. Because configurations
are encapsulated by servers, it makes more sense to me that the servers
(or server groups) would specify their configurations. If changing to a
more logical model is just too hard for TOSCA to adapt to, then I suggest
this be an area that TOSCA differs from Heat. We don't need two models
for communicating configurations to servers, and I'd prefer Heat stay
focused on making HOT template authors' and users' lives better.
I have seen an alternative approach which separates a configuration
definition from a configuration deployer. This at least makes it clear
that the configuration is a part of a server. In pseudo-HOT:
resources:
WebConfig:
type: OS::Heat::ChefCookbook
properties:
cookbook_url: https://some.test/foo
parameters:
endpoint_host:
type: string
WebServer:
type: OS::Nova::Server
properties:
image: webserver
flavor: 100
DeployWebConfig:
type: OS::Heat::ConfigDeployer
properties:
configuration: {get_resource: WebConfig}
on_server: {get_resource: WebServer}
parameters:
endpoint_host: {get_attribute: [ WebServer, first_ip]}
This is what Thomas defined, with one optimisation.
- The webconfig is a yaml template.
As you say the component is static - if so why even put it inline in
the template (well that was my thinking, it seems like a template not
really a resource).
I have implementation questions about both of these approaches though,
as it appears they'd have to reach backward in the graph to insert
their configuration, or have a generic bucket for all configuration
Yeah, it does depend on the implementation. If we use Mistral the
agent will need to ask Mistral for the tasks that apply to the server.
$ mistral task-consume \
--tags=instance_id=$(my_instance_id);stack_id=$(stack_id)
to be inserted. IMO that would look a lot like the method I proposed,
which was to just have a list of components attached directly to the
server like this:
components:
WebConfig:
type: Chef::Cookbook
properties:
cookbook_url: https://some.test/foo
parameters:
endpoing_host:
type: string
resources:
WebServer:
type: OS::Nova::Server
properties:
image: webserver
flavor: 100
components:
- webconfig:
component: {get_component: WebConfig}
parameters:
endpoint_host: {get_attribute: [ WebServer, first_ip ]}
I'd change this to:
components:
- webconfig:
component: {get_file: ./my_configs/webconfig.yaml}
parameters:
endpoint_host: {get_attribute: [ WebServer, first_ip ]}
This *could* be a short hand notation like the volumes property on
aws instances.
Of course, the keen eye will see the circular dependency there with the
WebServer trying to know its own IP. We've identified quite a few use
cases for self-referencing attributes, so that is a separate problem we
should solve independent of the template composition problem.
(aside) I don't like the idea of self ref as it breaks the idea that
references are resolved top down. Basically we have to put in
a nasty hack to produce broken behaviour (first resolution is
bogus and only following resoultions are possibly correct).
In this case just use the deployer to break your circular dep?
Anyway, I prefer the idea that parse-time things are called components
and run-time things are resources. I don't need a database entry for
"WebConfig" above. It is in the template and entirely static, just
sitting there as a reusable chunk for servers to pull in as-needed.
IMO is should just be a template/formatted file.
Anyway, I don't feel that we resolved any of these issues in the session
about configuration at the summit. If we did, we did not record them
in the etherpad or the blueprint. We barely got through the prepared
list of requirements and only were able to spell out problems, not
any solutions. So forgive me if I missed something and want to keep on
discussing this.
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