Open Stack

Ton, could you repost this as a new thread? It has very little to do
with the referenced thread.

Excerpts from Ton Ngo's message of 2014-03-17 12:10:33 -0700:
> I would like to revisit with more details an idea that was mentioned in the
> last design summit and hopefully get some feedback.
> 
> The scenario is troubleshooting a failed template.
> Currently we can stop on the point of failure by disabling rollback:  this
> works well for stack-create; stack-update requires some more work but
> that's different thread.  In many cases however, the point of failure may
> be too late or too hard to debug because the condition causing the failure
> may not be obvious or may have been changed.  If we can pause the stack at
> a point before the failure, then we can check whether the state of the
> environment and the stack is what we expect.
> The analogy with program debugging is breakpoint/step, so it may be useful
> to introduce this same concept in a stack.
> 
> The usage would be something like:
> -Run stack-create (or stack-update once it can handle failure) with one or
> more resource name specified as breakpoint
> -As the engine traverses down the dependency graph, it would stop at the
> breakpoint resource and all dependent resources.  Other resources with no
> dependency will proceed to completion.
> -After debugging, continue the stack by:
>     -Stepping: remove current breakpoint, set breakpoint for next resource
> (s) in dependency graph, resume stack-create (or stack-update)
>     -Running to completion: remove current breakpoint, resume stack-create
> (or stack-update)
> 
> Some other possible uses for this breakpoint:
> - While developing new template or resource type, bring up a stack to a
> point before the new code is to be executed
> - Introduce human process: pause the partial stack so the user can get the
> stack info and perform some tasks before continuing
> 
> Some issues to consider (with initial feedback from shardy):
> - Granularity of stepping:  resource level or internal steps within a
> resource
> - How to specify breakpoints:  CLI argument or coded in template or both
> - How to handle resources with timer, e.g. wait condition:  pause/resume
> timer value
> - New state for a resource:  PAUSED
> 
> Thanks.
> 
> Ton Ngo,
>