Wasm

Use Wasm programs as a filter.

Supported event types: logs

The Wasm filter lets you modify the incoming records using Wasm technology.

You can extend Fluent Bit capabilities by writing custom filters using built Wasm programs and its runtime. A Wasm-based filter takes the following steps:

1. (Optional) Compile Ahead Of Time (AOT) objects to optimize the Wasm execution pipeline.

2. Configure the filter in the main configuration.

3. Prepare a Wasm program that will be used by the filter.

Configuration parameters

The plugin supports the following configuration parameters:

Key	Description
accessible_paths	Specify the allowlist of paths to be able to access paths from Wasm programs. Default: . (current directory).
event_format	Define event format to interact with Wasm programs: msgpack or json. Default: json.
function_name	Wasm function name that will be triggered to do filtering. It's assumed that the function is built inside the Wasm program specified previously.
wasm_heap_size	Size of the heap size of Wasm execution. Review unit sizes for allowed values.
wasm_path	Path to the built Wasm program that will be used. This can be a path relative to the main configuration file.
wasm_stack_size	Size of the stack size of Wasm execution. Review unit sizes for allowed values.

Configuration example

Here is a configuration example.

fluent-bit.yaml

pipeline:
  inputs:
    - name: dummy
      tag: dummy.local

  filters:
    - name: wasm
      match: 'dummy.*'
      event_format: json    # or msgpack
      wasm_path: /path/to/wasm_program.wasm
      function_name: filter_function_name
      # Note: run Fluent Bit from the 'wasm_path' location.
      accessible_paths: /path/to/accessible

  outputs:
    - name: stdout
      match: '*'

fluent-bit.conf