Add "continue" as an error handling option for getMeta at initialization
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Key: UIMA-1295
URL: https://issues.apache.org/jira/browse/UIMA-1295
Project: UIMA
Issue Type: New Feature
Components: Async Scaleout
Reporter: Eddie Epstein
In http://markmail.org/message/ceb2npk5qsmuftn4 Yosi Mass requested that UIMA
support a peer-to-peer capability where services are discovered dynamically to
improve load balancing, and presumably, to enhance processing by using
analytics which only become available after a client has started.
UIMA AS already supports dynamically expanding processing capability for a
particular service, by simply starting additional service instances pointed at
the service's existing request queue. Using appropriate error handling and/or
custom flow controller options, a UIMA AS aggregate also has the capability to
ignore a missing delegate service, as long as the delegate service was
available during aggregate initialization. The enhancement suggested here is to
allow an aggregate service to later use a delegate service that was unavailable
during initialization.
UIMA changes would be:
1. add a new error handling option for getMeta failures at initialization.
Currently the options at init are to disable any use of the delegate, or fail
initialization and terminate the aggregate. The new option, "continue", would
be ignore this failure and complete initialization of the aggregate, but mark
the delegate as being in a special state, very similar to the "questionable"
state described in UIMA-1127.
2. The difference from UIMA-1127 is that when getMeta succeeds for this
delegate, the service's type system would be checked to see that it is
compatible with that of the aggregate. See UIMA-1290 for details on what
validation means. If valid, the delegate is marked fully operational. If the
type system fails validation, and process error handling is set to continue, a
new exception type would be given to the flow controller to decide how to
handle the situation.
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