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I'm trying to create an aggregate counter for various streams I have set up. In SpringXD it would look like this: "tap:stream:MyCustomStream > aggregate-counter".

In Spring Cloud Dataflow so far I have done ":MyKafkaTopic > aggregate-counter", which seems to create a Kafka consumer and read the payload to determine a count of events on the topic. I'd like to be able to tap any stream not just a Kafka source, e.g. "MyApp1 | MyApp2" --name MyCustomStream.

The provided example "stream create --definition ":mainstream.http > counter" --name tap_at_http --deploy" essentially assumes mainstream.http is a Kafka topic (or RabbitMQ topic).

Anyone done this before?

Kevin Niemann
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1 Answers1

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Going by your example,

stream create foo --definition "MyApp1 | MyApp2"

If you'd have to TAP the foo stream at the producer, MyApp1 level, your TAP stream would like the following.

stream create bar --definition ":foo.MyApp1 > MyApp3"

You're just pointing to the producer in the stream where you'd like to TAP to get a copy of same data. The format is: :<streamName>.<label/appName>. You could use "labels" instead of app names, too. Please review the reference guide for more details.

The provided example "stream create --definition ":mainstream.http > counter" --name tap_at_http --deploy" essentially assumes mainstream.http is a Kafka topic (or RabbitMQ topic).

In this case, mainstream is the stream name and you're TAP'ing at http source application, which equates to :mainstream.http.

This is analogous to tap:stream:foo in Spring XD. By default, Spring XD assumes the producer if there's only in the stream. You'd have to specify it when you TAP at the processor, though.

In SCDF, we require it specifically to make it more descriptive and the DSL is easy to follow as well.

Sabby Anandan
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