The fnrun project provides a set of tools for running business functions as a service.

The goal of fnrun is to provide a simple and extensible way to run business functions as a service. Its approach separates infrastructure concerns from the business functions, enabling application developers to build small business-focused functions and test in a variety of environments.

The fnrun project consists of an application called fnrunner and a Go library for building custom business functions and function runners.


fnrun contains four main concepts: sources, middleware, fns, and runners.

A source is a component that provides inputs to a business function and will handle the outputs. Some common sources include a web server that will receive HTTP requests and return HTTP responses and a queue client that will read messages from a queue and mark the messages as handled only if the business function returns an output successfully.

Middleware are components that process inputs received from sources before the input is sent to a business function. They also have an opportunity to manipulate the output or errors from the business function before being returned to the source. Middleware can be composed into a middleware pipeline, where data is passed through each middleware in order until the end of the pipeline is reached.

Fns are components that represent business functions. They can actually be business functions written in Go, but they are more commonly components that interact with an external business function. As an example, the CLI fn runs a business function as a CLI application and communicates with it over std streams.

A runner is a combination of a source, middleware, and an fn. The fnrun project provides a runner called fnrunner that provides common sources, middleware, and fns. However, it is also possible to create custom runners that include new components designed to meet the specific needs of your environment.


The fnrun project provides a runner called fnrunner which packages commonly used sources, middleware, and fns. fnrunner is an executable program that accepts a YAML file (fnrun.yaml by default) that configures a processing pipeline for events.

Following is an example fnrun.yaml file that is used to build a process that runs an HTTP server on port 8080, selects the body from a request, executes the request from a pool of CLI applications run as ./myprogram, and return the result as an HTTP response.

source: fnrun.source/http
  - fnrun.source/key: body
    concurrency: 8
      fnrun.fn/cli: ./myprogram

Details about the use and configuration of the all available components in fnrunner are located on this site.

fnrunner also accepts overrides for the default fnrun.yaml. The following order defines priority from highest to lowest:

  • CONFIG_FILE environment variable
  • -f FILE argument to fnrunner
  • default fnrun.yaml file


The fnrun project is designed to be deployed in a wide variety of environments ranging from servers to serverless. Deploying an fnrun project requires a runner, a business function, configuration files such as fnrun.yaml, and any execution environment required by the business function itself. These may be packaged and deployed to an environment such as a Docker container by whatever means supported by your organization.

It should be noted that fnrun does not provide autoscaling capabilities, but it is designed to work with systems that do provide this scalability such as Knative, AWS Lambda, and AWS Fargate.

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