Hi folks,
There have been requests for triggering a Pulsar Function just like one can
curl an AWS Lambda.
There can be several modes using different mechanisms that can be
supported. Just wanted to get community feedback around this.
The idea is that one can issue a curl command with payload to a Pulsar
Function running inside a Pulsar cluster and have the function work on the
payload. The output of the function, if any, should be the response of the
curl command.
There are several considerations
1. Since Pulsar Functions consume from a topic, should we publish the
message to the incoming topic. What if a function consumes from multiple
input topics. In that case which topics should we publish on? Also note
that publishing on input topic will also affect other consumers beside the
function in consideration.
2. What is the side-affects of running functions this way. For example if
they modify any counters, that would be globally seen. Is this reasonable
behavior? What about any outputs being published to output topic?
3. What is the best mechanism to implement such a functionality? If
side-effects are ok, then publish/consume is probably the easiest way to
implement it. Alternatively one can send the payload via grpc from the
brokers to the function instance to have it triggered. The state
side-effects concerns still exist in this scenario.

Any other concerns? Feedback is welcome.

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