WASM Input Plugins

WebAssembly (Wasm) is a binary instruction format for stack-based virtual machines.

Fluent Bit supports integration of Wasm plugins built as Wasm/WASI objects for inputs and filter plugins only. The interface for Wasm filter plugins is currently under development but is functional.

Prerequisites

Build Fluent Bit

There are no additional requirements to execute Wasm plugins.

For Wasm programs

Fluent Bit supports the following Wasm toolchains:

• Rust on wasm32-unknown-unknown

  • rustc 1.62.1 (e092d0b6b 2022-07-16) or later

• TinyGo on wasm32-wasi

  • v0.24.0 or later

• WASI SDK 13 or later

Get started

Compile Fluent Bit with Wasm support. For example:

$ cd build/
$ cmake ..
$ make

Once compiled, you can see new plugins that handle wasm. For example:

$ bin/fluent-bit -h
Usage: fluent-bit [OPTION]
Inputs
  # ... other input plugin stuffs
  exec_wasi               Exec WASI Input

Filters
  # ... other filter plugin stuffs
  wasm                    WASM program filter

Build a Wasm input for input plugin

Wasm input in Fluent Bit assumes WASI ABI, also known as wasm32-wasi on Rust target and wasm32-wasi on TinyGo target.

Install additional components

TinyGo and WASI SDK support Wasm target by default. When using Rust's wasm32-wasi target, you must install wasm32-wasi by using rustup. Then, install the target components as:

$ rustup target add wasm32-wasi

Requirements of Wasm/WASI programs

Wasm input plugins execute the function that has a WASI main function entrypoint, and Wasm input plugins in Fluent Bit communicate through stdout on Wasm programs.

Wasm programs should handle stdout for ingesting logs into Fluent Bit.

Once built, a Wasm/WASI program will be available. Then you can execute that built program with the following Fluent Bit configuration:

[INPUT]
    Name exec_wasi
    Tag  exec.wasi.local
    WASI_Path /path/to/wasi_built_json.wasm
    # For security reasons, WASM/WASI program cannot access its outer world
    # without accessible permissions.
    # accessible_paths .,/path/to/fluent-bit

[OUTPUT]
    Name  stdout
    Match *

For an example that handles structured logs, see the Rust serde-json example.