Dear Steve and All,
If I may add up on this already busy thread to share our experience with
using Heat in large and complex software deployments.
I work on a project which precisely provides additional value at the
articulation point between resource orchestration automation and
configuration management. We rely on Heat and chef-solo respectively for
these base management functions. On top of this, we have developed an
event-driven workflow to manage the life-cycles of complex software
stacks which primary purpose is to support middleware components as
opposed to end-user apps. Our use cases are peculiar in the sense that
software setup (install, config, contextualization) is not a one-time
operation issue but a continuous thing that can happen any time in
life-span of a stack. Users can deploy (and undeploy) apps long time
after the stack is created. Auto-scaling may also result in an
asynchronous apps deployment. More about this latter. The framework we
have designed works well for us. It clearly refers to a PaaS-like
environment which I understand is not the topic of the HOT software
configuration proposal(s) and that's absolutely fine with us. However,
the question for us is whether the separation of software config from
resources would make our life easier or not. I think the answer is
definitely yes but at the condition that the DSL extension preserves
almost everything from the expressiveness of the resource element. In
practice, I think that a strict separation between resource and
component will be hard to achieve because we'll always need a little bit
of application's specific in the resources. Take for example the case of
the SecurityGroups. The ports open in a SecurityGroup are application
specific.
Then, designing a Chef or Puppet component type may be harder than it
looks at first glance. Speaking of our use cases we still need a little
bit of scripting in the instance's user-data block to setup a working
chef-solo environment. For example, we run librarian-chef prior to
starting chef-solo to resolve the cookbook dependencies. A cookbook can
present itself as a downloadable tarball but it's not always the case. A
chef component type would have to support getting a cookbook from a
public or private git repo (maybe subversion), handle situations where
there is one cookbook per repo or multiple cookbooks per repo, let the
user choose a particular branch or label, provide ssh keys if it's a
private repo, and so forth. We support all of this scenarios and so we
can provide more detailed requirements if needed.
I am not sure adding component relations like the 'depends-on' would
really help us since it is the job of config management to handle
software dependencies. Also, it doesn't address the issue of circular
dependencies. Circular dependencies occur in complex software stack
deployments. Example. When we setup a Slum virtual cluster, both the
head node and compute nodes depend on one another to complete their
configuration and so they would wait for each other indefinitely if we
were to rely on the 'depends-on'. In addition, I think it's critical to
distinguish between configuration parameters which are known ahead of
time, like a db name or user name and password, versus contextualization
parameters which are known after the fact generally when the instance is
created. Typically those contextualization parameters are IP addresses
but not only. The fact packages x,y,z have been properly installed and
services a,b,c successfully started is contextualization information
(a.k.a facts) which may be indicative that other components can move on
to the next setup stage.
The case of complex deployments with or without circular dependencies is
typically resolved by making the system converge toward the desirable
end-state through running idempotent recipes. This is our approach. The
first configuration phase handles parametrization which in general
brings an instance to CREATE_COMPLETE state. A second phase follows to
handle contextualization at the stack level. As a matter of fact, a new
contextualization should be triggered every time an instance enters or
leave the CREATE_COMPLETE state which may happen any time with
auto-scaling. In that phase, circular dependencies can be resolved
because all contextualization data can be compiled globally. Notice that
Heat doesn't provide a purpose built resource or service like Chef's
data-bag for the storage and retrieval of metadata. This a gap which IMO
should be addressed in the proposal. Currently, we use a kludge that is
to create a fake AWS::AutoScaling::LaunchConfiguration resource to store
contextualization data in the metadata section of that resource.
Aside from the HOT software configuration proposal(s). There are two
critical enhancements in Heat that would make software life-cycles
management much easier. In fact, they are actual blockers for us.
The first one would be to support asynchronous notifications when an
instance is created or deleted as a result of an auto-scaling decision.
As stated earlier, contextualization needs to apply in a stack every
time a instance enters or leaves the CREATE_COMPLETE state. I am not
referring to a Ceilometer notification but a Heat notification that can
be consumed by a Heat client.
The second one would be to support a new type of AWS::IAM::User (perhaps
OS::IAM::User) resource whereby one could pass Keystone credentials to
be able to specify Ceilometer alarms based on application's specific
metrics (a.k.a KPIs).
I hope this is making sense to you and can serve as a basis for further
discussions and refinements.
Cheers,
Patrick
On 10/16/13 12:48 AM, Steve Baker wrote:
I've just written some proposals to address Heat's HOT software
configuration needs, and I'd like to use this thread to get some feedback:
https://wiki.openstack.org/wiki/Heat/Blueprints/hot-software-config
https://wiki.openstack.org/wiki/Heat/Blueprints/native-tools-bootstrap-config
Please read the proposals and reply to the list with any comments or
suggestions.
We can spend some time discussing software configuration at tomorrow's
Heat meeting, but I fully expect we'll still be in the discussion
phase at Hong Kong.
cheers
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Patrick Petit
Cloud Computing Principal Architect, Innovative Products
Bull, Architect of an Open World TM
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