Introduction to Fn with Node.js

Fn is a lightweight Docker-based serverless functions platform you can run on your laptop, server, or cloud. In this introductory tutorial we’ll walk through developing a function using the JavaScript programming language and Node.js (without installing any Node.js tools!) and deploying that function to a local Fn server. We’ll also learn about the core Fn concepts like applications and triggers.

Before you Begin

  • Set aside about 15 minutes to complete this tutorial.
  • Make sure Fn server is up and running by completing the Install and Start Fn Tutorial.
    • Make sure you have set your Fn context registry value for local development. (for example, “fndemouser”. See here.)

As you make your way through this tutorial, look out for this icon. Whenever you see it, it’s time for you to perform an action.

Your First Function

Now that Fn server is up and running, let’s start with a very simple “hello world” function written in Node.js JavaScript. Don’t worry, you don’t need to know Node! In fact you don’t even need to have Node installed on your development machine as Fn provides the necessary Node tools as a Docker container. Let’s walk through your first function to become familiar with the process and how Fn supports development.

Create your Function

In the terminal type the following.

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fn init --runtime node --trigger http nodefn

The output will be

Creating function at: /nodefn
Runtime: node
Function boilerplate generated.
func.yaml created.

The fn init command creates a simple function with a bit of boilerplate to get you started. The --runtime option is used to indicate that the function we’re going to develop will be written in Node. A number of other runtimes are also supported. The --trigger option creates an HTTP trigger for the function allowing you to invoke the function from a URL. Fn creates the simple function along with several supporting files in the /nodefn directory.

Review your Function File

With your function created change into the /nodefn directory.

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cd nodefn

Now get a list of the directory contents.

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func.js func.yaml package.json

The func.js file which contains your actual Node function is generated along with several supporting files. To view your Node function type:

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cat func.js
const fdk=require('@fnproject/fdk');

  let name = 'World';
  if (input.name) {
    name = input.name;
  return {'message': 'Hello ' + name}

This function looks for JSON input in the form of {"name": "Bob"}. If this JSON example is passed to the function, the function returns {"message":"Hello Bob"}. If no JSON data is found, the function returns {"message":"Hello World"}.

Understand func.yaml

The fn init command generated a func.yaml function configuration file. Let’s look at the contents:

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cat func.yaml
schema_version: 20180708
name: nodefn
version: 0.0.1
runtime: node
entrypoint: node func.js
- name: nodefn-trigger
  type: http
  source: /nodefn-trigger

The generated func.yaml file contains metadata about your function and declares a number of properties including:

  • schema_version–identifies the version of the schema for this function file. Essentially, it determines which fields are present in func.yaml.
  • name–the name of the function. Matches the directory name.
  • version–automatically starting at 0.0.1.
  • runtime–the name of the runtime/language which was set based on the value set in --runtime.
  • entrypoint–the name of the executable to invoke when your function is called, in this case node func.js.
  • triggers–identifies the automatically generated trigger name and source. For example, this function would be requested from the URL http://localhost:8080/t/appname/nodefn-trigger. Where appname is the name of the app chosen for your function when it is deployed.

There are other user specifiable properties but these will suffice for this example. Note that the name of your function is taken from the containing folder name. We’ll see this come into play later on.

Other Function Files

The fn init command generated one other file.

  • package.json – specifies all the Node.js dependencies for your Node function.

Fn and Node.js Dependencies

Fn handles Node.js dependencies in the following way:

  • If a package.json is present without a node_modules directory, an Fn build runs an npm install within the build process and installs your dependencies.
  • If the node_modules is present, Fn assumes you have provided the dependencies yourself and no installation is performed.

Deploy Your First Function

With the nodefn directory containing func.js and func.yaml you’ve got everything you need to deploy the function to Fn server. This server could be running in the cloud, in your datacenter, or on your local machine like we’re doing here.

Check your Context

Make sure your context is set to default and you are using a demo user. Use the fn list contexts command to check.

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fn list contexts
*       default	default		http://localhost:8080	fndemouser

If your context is not configured, please see the context installation instructions before proceeding. Your context determines the server your function is deployed to.

Create an App

Next, functions are grouped together into an application. The application acts as the main organizing structure for multiple functions. To create an application type the following:

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fn create app nodeapp

A confirmation is returned:

Successfully created app:  nodeapp

Now nodeapp is ready for functions to be deployed to it.

Deploy your Function to your App

Deploying your function is how you publish your function and make it accessible to other users and systems. To see the details of what is happening during a function deploy, use the --verbose switch. The first time you build a function of a particular language it takes longer as Fn downloads the necessary Docker images. The --verbose option allows you to see this process.

In your terminal type the following:

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fn --verbose deploy --app nodeapp --local

You should see output similar to:

Deploying nodefn to app: nodeapp
Bumped to version 0.0.2
Building image fndemouser/nodefn:0.0.2 
FN_REGISTRY:  fndemouser
Current Context:  default
Sending build context to Docker daemon   5.12kB
Step 1/9 : FROM fnproject/node:dev as build-stage
dev: Pulling from fnproject/node
cd784148e348: Pull complete 
b44a6bdc3ce6: Pull complete 
4a521620f99f: Pull complete 
Digest: sha256:af86804c77b827efefa7f16395908f47842558382ab2cbdfcba8d78ab912c711
Status: Downloaded newer image for fnproject/node:dev
 ---> 1959078abed4
Step 2/9 : WORKDIR /function
 ---> Running in bae6000b50b2
Removing intermediate container bae6000b50b2
 ---> 5c8692d1e321
Step 3/9 : ADD package.json /function/
 ---> 8a609ca9d62d
Step 4/9 : RUN npm install
 ---> Running in ac0389a21058
npm notice created a lockfile as package-lock.json. You should commit this file.
npm WARN [email protected] No repository field.

added 1 package from 2 contributors and audited 1 package in 1.628s
found 0 vulnerabilities

Removing intermediate container ac0389a21058
 ---> f27015c4e988
Step 5/9 : FROM fnproject/node
latest: Pulling from fnproject/node
Digest: sha256:af86804c77b827efefa7f16395908f47842558382ab2cbdfcba8d78ab912c711
Status: Downloaded newer image for fnproject/node:latest
 ---> 1959078abed4
Step 6/9 : WORKDIR /function
 ---> Using cache
 ---> 5c8692d1e321
Step 7/9 : ADD . /function/
 ---> 322790c57f6a
Step 8/9 : COPY --from=build-stage /function/node_modules/ /function/node_modules/
 ---> 71035a700e7f
Step 9/9 : ENTRYPOINT ["node", "func.js"]
 ---> Running in 85aaa3aa14eb
Removing intermediate container 85aaa3aa14eb
 ---> 9f6cf7646cdf
Successfully built 9f6cf7646cdf
Successfully tagged fndemouser/nodefn:0.0.2

Updating function nodefn using image fndemouser/nodefn:0.0.2...
Successfully created function: nodefn with fndemouser/nodefn:0.0.2
Successfully created trigger: nodefn-trigger
Trigger Endpoint: http://localhost:8080/t/nodeapp/nodefn-trigger

All the steps to load the current language Docker image are displayed.

Specifying --app nodeapp explicitly puts the function in the application “nodeapp”.

Specifying --local does the deployment to the local server but does not push the function image to a Docker registry–which would be necessary if we were deploying to a remote Fn server.

The output message Updating function nodefn using image fndemouser/nodefn:0.0.2... let’s us know that the function is packaged in the image “fndemouser/nodefn:0.0.2”.

Note that the containing folder name ‘nodefn’ was used as the name of the generated Docker container and used as the name of the function that container was bound to. By convention it is also used to create the trigger name nodefn-trigger.

Normally you deploy an application without the --verbose option. If you rerun the command a new image and version is created and loaded.

Invoke your Deployed Function

There are two ways to call your deployed function.

Invoke with the CLI

The first is using the fn CLI which makes invoking your function relatively easy. Type the following:

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fn invoke nodeapp nodefn

which results in:

{"message":"Hello World"}

When you invoked “nodeapp nodefn” the fn server looked up the “nodeapp” application and then looked for the Docker container image bound to the “nodefn” function and executed the code.

You can also pass data to the run command. Note that you set the content type for the data passed. For example:

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echo -n '{"name":"Bob"}' | fn invoke nodeapp nodefn --content-type application/json
{"message":"Hello Bob"}

The JSON data was parsed and since name was set to “Bob”, that value is passed in the output.

Understand fn deploy

If you have used Docker before the output of fn --verbose deploy should look familiar–it looks like the output you see when running docker build with a Dockerfile. Of course this is exactly what’s happening! When you deploy a function like this Fn is dynamically generating a Dockerfile for your function, building a container, and then loading it for execution.

NOTE: Fn is actually using two images. The first contains the language compiler and all the necessary build tools. The second image packages all dependencies and any necessary language runtime components. Using this strategy, the final function image size can be kept as small as possible. Smaller Docker images are naturally faster to push and pull from a repository which improves overall performance. For more details on this technique see Multi-Stage Docker Builds for Creating Tiny Go Images.

When using fn deploy --local, fn server builds and packages your function into a container image which resides on your local machine.

As Fn is built on Docker you can use the docker command to see the local container image you just generated. You may have a number of Docker images so use the following command to see only those created by fndemouser:

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docker images | grep fndemouser

You should see something like:

fndemouser/nodefn    0.0.2               b9330bddec26        2 minutes ago      66.4MB

Explore your Application

The fn CLI provides a couple of commands to let us see what we’ve deployed. fn list apps returns a list of all of the defined applications.

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fn list apps

Which, in our case, returns the name of the application we created when we deployed our nodefn function:


We can also see the functions that are defined by an application. Since functions are exposed via triggers, the fn list triggers <appname> command is used. To list the functions included in “nodeapp” we can type:

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fn list triggers nodeapp
FUNCTION    NAME             TYPE    SOURCE          ENDPOINT
nodefn      nodefn-trigger   http    /nodefn-trigger http://localhost:8080/t/nodeapp/nodefn-trigger

The output confirms that nodeapp contains a nodefn function that can be called via this URL.

Invoke with Curl

The other way to invoke your function is via HTTP. The Fn server exposes our deployed function at http://localhost:8080/t/nodeapp/nodefn-trigger, a URL that incorporates our application and function trigger as path elements.

Use curl to invoke the function:

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curl -H "Content-Type: application/json" http://localhost:8080/t/nodeapp/nodefn-trigger

The result is once again the same.

{"message":"Hello World"}

We can again pass JSON data to our function get the value of name passed to the function back.

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curl -H "Content-Type: application/json" -d '{"name":"Bob"}' http://localhost:8080/t/nodeapp/nodefn-trigger

The result is once again the same.

{"message":"Hello Bob"}

Wrap Up

Congratulations! In this tutorial you’ve accomplished a lot. You’ve created your first function, deployed it to your local Fn server and invoked it over HTTP.

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