Testing a running Fn locally

Running functions that call other functions in a local testing environment can be challenging. This document will outline best practices in functions to make this work more easily between deployments as well as some tips to help testing locally.

Best Practices

Included in each function invocation will be the request url for how the function was invoked. In FDKs, this will be exposed in the context object for each language. If your function invokes other functions, it's recommended to either configure the host that your function should use to invoke the other functions yourself (by sending it in the payload, or elsewhere), or to parse the request_url that Fn includes in a function invocation and use that. This makes it easy to switch between e.g. localhost:8080 and fn.my-company.com.

Configuring functions to invoke locally

When running functions that call other functions locally, they will need to be able to address the fn server to do so. Since functions run in a docker container, this can be more challenging when using a localhost url. One option is to use something more heavyweight like ngrok, and this will work. It is also possible in a local environment to start fn with the option FN_DOCKER_NETWORKS=host, this is equivalent to running each function container with --net=host, where each function can address the locally running fn server to invoke functions against on localhost; this setting is not recommended for production and any behaviors therein should not be expected in production, it is extremely convenient for testing locally nonetheless.