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SmartModules are one of Fluvio’s premiere features, allowing users to have direct control over their streaming data by providing a programmable API for inline data manipulation. SmartModules are user-defined functions, written in Rust and compiled to WebAssembly - that means they’re lightweight and portable, and enable enormous flexibility for being integrated at many points in a streaming pipeline. They enhance the entire streaming platform: reducing network costs by allowing precision filtering along the stream and encouraging code-reuse and collaboration.

The following diagram shows common components which may be configured with SmartModules performing inline computation.

SmartModule Overview

The diagram shows five places where SmartModules may currently be used:

  • In Source Connectors and Sink Connectors, and
  • in programmatic Producers, Consumers, and the Fluvio CLI

SmartModules are typically applied to data before the data is sent from one location to another. This is so that any filtering that happens will result in less network traffic and more savings. For example, stream inputs (i.e. Source Connectors and Producers) will apply SmartModules before sending data to the Fluvio cluster, and stream outputs (such as Sink Connectors, Consumers, and the Fluvio CLI) will upload SmartModules to the Fluvio cluster and process data before the stream is sent over the network. This helps to overcome “Data Gravity” by moving only the most minimal amount of data necessary.


Types of SmartModules

Fluvio features the following types of SmartModules:





A Filter SmartModule takes an input record and returns false if the record should be discarded, or true if the record should be kept and sent downstream.

SmartModule Filter


A Map SmartModule takes an input record and may edit and transform it, returning a new record that is sent downstream.

SmartModule Map


A FilterMap SmartModule takes one input record and returns zero or one output record. This effectively means that it may decide to discard or “filter” any input records, or to keep them and apply a transformation to them at the same time.

SmartModule FilterMap


An ArrayMap SmartModule takes one input record and returns zero or many output records. This means that the output stream may have more records than the input stream.

SmartModule ArrayMap




An Aggregate SmartModule takes input records and “accumulates” them, essentially adding each input record to a rolling sum. Each input record gets “added” to the sum after the previous record, and the output stream is full of the “summed” records.

SmartModule Aggregate

Building SmartModules

Fluvio SmartModule generator creates a Cargo project with all the necessary boilerplate to get you up and running quickly.


In Rust

Install cargo-generate if you didn’t install before (one time operation):

$ cargo install cargo-generate 

Run SmartModule template generator:

$ cargo generate --git https://github.com/infinyon/fluvio-smartmodule-template
⚠️   Unable to load config file: /.cargo/cargo-generate.toml
🤷   Project Name : my-filter
🔧   Generating template ...
✔ 🤷   Which type of SmartModule would you like? · filter
✔ 🤷   Want to use SmartModule parameters? · true
[1/7]   Done: .cargo/config.toml
[2/7]   Done: .cargo
[3/7]   Done: .gitignore
[4/7]   Done: Cargo.toml
[5/7]   Done: README.md
[6/7]   Done: src/lib.rs
[7/7]   Done: src
🔧   Moving generated files into: `/my-filter`...
💡   Initializing a fresh Git repository
✨   Done! New project created /my-filter

Navigate to your SmartModule directory, make your changes, then compile:

$ cargo build --release

Now that we have the SmartModule binary compiled let’s see it in action.


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Registering SmartModules

After building a SmartModule as a WASM binary, it may be registered with Fluvio using the fluvio smart-module command, providing a name and a path to the binary. Use SmartModule filters to build a WASM file.

$ fluvio smart-module create my-filter --wasm-file=target/wasm32-unknown-unknown/release/my_filter.wasm

After creating one or more SmartModules, one may use the fluvio smart-module list command to see the available SmartModules:

$ fluvio smart-module list
 NAME       STATUS             SIZE
 my-filter  SmartModuleStatus  108754

Using SmartModules

SmartModules may be used in two ways: by registering them by name with the Fluvio cluster, or by providing them “ad hoc” right when you want to use them. In development, it is useful to use ad-hoc SmartModules, since the compiled WASM code is changing between each run. However, for most actual use-cases, it typically becomes much easier to register the SmartModule and later refer to them by name.


In Consumers


Using Registered SmartModules

You may use a Registered SmartModule anywhere that SmartModules may be used. To use them, you’ll need to provide the name of the SmartModule as well as its type.

For example, when using a registered filter SmartModule with the Fluvio CLI Consumer, provide its name to the --filter argument, like so:

$ fluvio consume my-topic -B --filter=my-filter

Using Inline SmartModules

You may still use SmartModules even without registering them with Fluvio. When using SmartModules this way, you simply provide a path to the WASM file directly when you use it. For example, when using an ad-hoc SmartModule with the Fluvio CLI Consumer, you may pass a file path to --filter that points to the SmartModule WASM file, like this:

$ fluvio consume my-topic -B --filter=target/wasm32-unknown-unknown/release/my_filter.wasm

In Connectors

SmartModules can be applied to any source or sink connector. A SmartConnector devides the collector logic from the data logic. For example, the http source connector, can filter or map data fields before publishing to the topic:

# connect.yml
name: my-sink-connector
type: http
topic: my-topic
create_topic: true
direction: source
  endpoint: https://catfact.ninja/fact
  interval: 30
  filter: my-filter 

In this example, the connector reads cat facts and filters out cat statements based on the criteria defined in the SmartModule. For additional information, check out the SmartConnectors section.