riff Function Streaming Processor

This repository contains the sources of the riff function streaming processor, a component used when dealing with streaming functions.

Purpose

When dealing with streaming functions, one creates a processor in riff like so:

riff streaming processor create example --function-ref some-existing-fn \
    --input  input-stream \
    --input  i2:maybe-another-input \
    --output some-output-stream \
    --output out3:maybe-another \
    --output even-a-third

This creates a pod made of two containers. This component will run in the function pod, alongside the function container, and will

1. continuously pump data from any of the function input streams (input-stream and maybe-another-input in the example above) out of the stream gateway(s)

2. extract the message payloads from the serialized form used in the broker(s).

3. decide how to craft windows of function invocation (currently hardcoded to one minute of wallclock time)

4. invoke the function over RPC, multiplexing the many input streams over the single stream allowed by the RPC spec (see riff-rpc.proto)

5. upon reception of result frames, de-mux messages and serialize them back to the appropriate output streams (some-output-stream, maybe-another and even-a-third in the example above).

Notice that the number of input and output streams can be different and depends entirely on how the actual function is implemented. Likewise, the rate at which messages flow in and out is entirely dictated by the function implementation (one piece of input may trigger the emission of N output messages, in quick succession or over time).

Building

This component is written in Java and leverages the following technologies:

• Spring Boot as the overall framework, in particular for crafting an executable jar,

• Liiklus as the stream gateway,

• gRPC as both the RPC protocol to interact with liiklus and the riff RPC invocation protocol,

• Reactor and reactor-grpc as the main event loop mechanism, preserving back-pressure from output to input.

To build the project, assuming a fresh checkout of this repository as the current directory:

mvn package

To build and create (and push) a docker image:

mvn package com.google.cloud.tools:jib-maven-plugin:1.3.0:build -Dimage=<MY IMAGE>

To create (and push) a docker image containing a native version:

mvn package && docker build . -t <MY NATIVE IMAGE> && docker push <MY NATIVE IMAGE>

Running

When run, the processor expects the following environment variables to be set:

• INPUT_NAMES: a comma separated list of N input parameter logical names,

• OUTPUT_NAMES: a comma separated list of M output result logical names,

• GROUP: a string identifier that will be used as the consumer group for the processor.

• FUNCTION: location of the function RPC server, in the form host:port,

• INPUT_START_OFFSETS: a comma separated list of N strings (each earliest or latest) to drive where to start subscribing from for each input,

• CNB_BINDINGS: directory location of stream bindings information. The processor will read N bindings at $CNB_BINDINGS/input_xxx and M bindings at $CNB_BINDINGS/output_xxx.