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[API Redesign] Add proposal to improve fault tolerance

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Related to #79
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Victor Woeltjen 2015-09-11 12:26:45 -07:00
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docs/src/design/proposals/APIRedesign.md
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@ -180,6 +180,11 @@ to develop a tabular visualization plugin.
* Add a model property to the bundle.json to take in "Hello World"
as a parameter and pass through to the controller/view
### Open Source Contributer
* [Failures are non-graceful when services are missing.](
https://github.com/nasa/openmctweb/issues/79)
## Misc. Feedback (mostly verbal)
* Easy to add things.
@ -950,3 +955,48 @@ a telemetry series.
* Merging with `subscribe` may lose the clarity/simplicity of the
current API.
## Allow Composite Services to Fail Gracefully
Currently, when no providers are available for a composite service
that is depended-upon, dependencies cannot be resolved and the
application fails to initialize, with errors appearing in the
developer console.
This is acceptable behavior for truly unrecoverable missing
dependencies, but in many cases it would be preferable to allow a
given type of composite service to define some failure behavior
when no service of an appropriate type is available.
To address this:
* Provide an interface (preferably
[imperative](#bundle-Declarations-in-javascript))
for declaring composite services, independent of any implementation
of an aggregator/decorator/provider. This allows the framework
layer to distinguish between unimplemented dependencies (which
could have defined failover strategies) from undefined dependencies
(which cannot.)
* Provide a default strategy for service composition that picks
the highest-priority provider, and logs an error (and fails to
satisfy) if no providers have been defined.
* Allow this aggregation strategy to be overridden, much as one
can declare aggregators currently. However, these aggregators should
get empty arrays when no providers have been registered (instead of
being ignored), at which point they can decide how to handle this
situation (graceful failure when it's possible, noisy errors when
it is not.)
### Benefits
* Allows for improved robustness and fault tolerance.
* Makes service declarations explicit, reducing "magic."
### Detriments
* Requires the inclusion of software units which define services,
instead of inferring their existence (slight increase in amount
of code that needs to be written.)
* May result in harder-to-understand errors when overridden
composition strategies do not failover well (that is, when they
do need at least implementation, but fail to check for this.)