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A Hello World App

Let's see how Jamsocket works by using it to spawn a little Hello World server.


We'll also want to use the Jamsocket CLI to manage our Jamsocket services and interact with Jamsocket's container registry. It's generally recommended to install the Jamsocket CLI either globally or in your project root with npm install jamsocket (or npm install jamsocket --global).

If you install the CLI globally on your machine, you may want to use a tool like Node Version Manager to manage your NodeJS binaries. (You can read more about that here.)

Logging in

Once you've got the CLI installed, you'll need to run npx jamsocket login to log in.

Creating a Service

First, we'll want to create a service for our Hello World project. We'll refer to the service's name whenever we push containers and spawn backends. We can create a new service with the CLI:

npx jamsocket service create hello-world

Our Hello World will be a simple NodeJS HTTP server. So let's create a server.js file in our project root with the following code:

const http = require('http')
const PORT = process.env.PORT

const server = http.createServer((req, res) => {
  res.end('Hello World')

server.listen(PORT, () => {
  console.log(`Server running at${PORT}/`)

Packaging a Container

Next, we need to package our backend into a container. All a container needs to be compatible with Jamsocket is to serve an HTTP server on port 8080 (which is also provided through $PORT for compatibility with Heroku-ready containers).

Let's use Docker to create a container for our app. We'll just need to write a Dockerfile that tells Docker how to build a containerized version of our application. Create a file named Dockerfile in your project root and add these lines to it:

FROM node:16
COPY server.js .
CMD ["node", "server.js"]

Now, let's use the Docker CLI to build the container and name it hello-world-image. (Note: Jamsocket currently runs backends on nodes with an x86 architecture. If you are building the container on an x86 machine, like an Intel Mac, you don't need the --platform linux/amd64 flag.)

docker build --platform linux/amd64 --tag hello-world-image .

Great! You should be able to run docker images now and see your new hello-world-image container image in the list.


Now that we've containerized our application, we just need to push the container image to our new hello-world service on Jamsocket.

npx jamsocket push hello-world hello-world-image


Let's spawn an instance of our service.

npx jamsocket spawn hello-world

You should see a result like this:

backend name:  1e9w4
backend url:
status url:
ready url:

Open the ready url in your browser. It serves as a temporary landing page while your backend spins up. You'll be redirected to the backend url once it's ready. Note that, in some cases, you might not get to see the landing page before you're redirected to the ready container. For more information on what else is contained the spawn command's response, see the Spawn a Service section of the API Docs.

Getting Logs

Finally, let's get some logs from our running container.

npx jamsocket logs 1e9w4

You should see your server logs in the output.

2022-05-05T13:00:00.123456789Z Server running at

Spawn one of our example apps

Our Hello World app is simple enough to demonstrate how pushing code and deploying backends works on Jamsocket, but it doesn't really show off the power of building applications with stateful backends. To see how session backends make multiplayer games and collaborative applications easier to build, check out one of our demos below.

Demo Description Image
Drop Four Drop Four (aka Connect 4) game example from Aper
Jupyter Notebook Jupyter notebook

To run one of these demos, simply pull the image down, create a new Jamsocket service, push the image to your service, and spawn. Here's an example:

docker pull
npx jamsocket service create drop-four-demo
npx jamsocket push drop-four-demo
npx jamsocket spawn drop-four-demo

Open the ready url in your browser to try out the demo. For collaborative demos, like the Drop Four and Chrome demos, open the ready url in two different tabs to see how application state is shared between them.