Michael Park created MESOS-7702:
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Summary: Fix the validation / conversion strategy of `Resources`.
Key: MESOS-7702
URL: https://issues.apache.org/jira/browse/MESOS-7702
Project: Mesos
Issue Type: Bug
Reporter: Michael Park
With reservation refinement, we introduced the "post-reservation-refinement"
format which uses a new {{Resource.reservations}} field to represent the
reservation state of a resource. The "pre-reservation-refinement" format used
the {{Resource.role}} and {{Resource.reservation}}.
In order to avoid writing two code paths for everything in every component, the
general strategy is to convert the resource format at the component boundaries.
That is, convert to the "post-reservation-refinement" format in-bound, and
convert back as necessary out-bound.
While I think this strategy is still good, the mechanism of how this happens
really needs to change.
It's very hard to tell and keep track of the state of {{Resource}} objects and
at what point they've been validated and have been converted.
For example, can we afford to call {{convertResourceFormat}} *after*
{{validation::operation::validate}}? Since {{operation::validate}} calls
{{Resources::validate}} within it, it may seem innocent to convert after the
operation has been validated. The issue though is that after
{{Resources::validate}} has been called within {{operation::validate}}, it
starts to use functions that require resources to be validated, and in the
"post-reservation-refinement" format. What this means is that validation and
conversion has a much tighter relationship than is enforced currently.
Besides the complexity that I added during reservation refinement, I also
believe that we already have some tech-debt in this area. For example, the
{{Resources}} constructor simply __drops__ invalid resources. This is really
subtle, and would be a nightmare to track down. I think a better approach would
be to have a creation function that can fail correctly. Since we live in a
world with no exceptions, this can be solved by having a creation function that
returns a {{Try}}. That is, {{Try<Resources> createResources(...);}} would do
the validation and return an {{Error}} on failure. Note that we can also bundle
the __conversion__ logic here as well.
* https://reviews.apache.org/r/60253/
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