node package manager
Share your code. npm Orgs help your team discover, share, and reuse code. Create a free org »



Join the chat at

SocketCluster logo

Complete documentation available at:

Documentation for SCC is available at


SocketCluster is a fast, highly scalable HTTP + realtime server engine which lets you build multi-process realtime servers that make use of all CPU cores on a machine/instance. It removes the limitations of having to run your Node.js server as a single thread and makes your backend resilient by automatically recovering from worker crashes and aggregating errors into a central log on each host. SC can also auto-scale across multiple hosts on top of Kubernetes; see SCC guide:

Follow the project on Twitter: Subscribe for updates:


There are two ways to install SocketCluster.

The easy way (Sets up boilerplate - Ready to run):

Setup the socketcluster command:

npm install -g socketcluster


sudo npm install -g socketcluster


socketcluster create myapp

Once it's installed, go to your new myapp/ directory and launch with:

node server

Access at URL http://localhost:8000/

The hard way (More modular - Separate server and client):

npm install socketcluster

You will also need to install the client separately which you can get using the following command:

npm install socketcluster-client

The socketcluster-client script is called socketcluster.js (located in the main socketcluster-client directory)

It is recommended that you use Node.js version >=0.10.22 due to memory leaks present in older versions.

Using over HTTPS

In order to run SocketCluster over HTTPS, all you need to do is set the protocol to 'https' and provide your private key and certificate as a start option when you instantiate SocketCluster - Example:

var socketCluster = new SocketCluster({
  workers: 3,
  brokers: 3,
  port: 8000,
  appName: 'myapp',
  workerController: 'worker.js',
  protocol: 'https',
  protocolOptions: {
    key: fs.readFileSync(__dirname + '/keys/enc_key.pem', 'utf8'),
    cert: fs.readFileSync(__dirname + '/keys/cert.pem', 'utf8'),
    passphrase: 'passphase4privkey'

The protocolOptions option is exactly the same as the one you pass to a standard Node HTTPS server:

Docker and SocketCluster

You can create an app on top of SocketCluster's docker image. The SC container can be run standalone or as a base image for your own container.

The official SocketCluster container on DockerHub is here:

The Dockerfile for the base image is here:

To use the SocketCluster container as your base image, your app's Dockerfile might look like this:

FROM socketcluster/socketcluster

LABEL version="1.0.0"
LABEL description="Custom app based on SocketCluster"

WORKDIR /usr/src/
COPY . /usr/src/

RUN npm install


CMD ["npm", "start"]

Then you can just build your container using:

docker build -t my-socketcluster-app:v1.0.0 .

Note that there are more ways to run SocketCluster with Docker. You can also mount your own volumes and point to custom worker.js and broker.js files which are inside those volumes using environment variables. You can see the environment variables which are used by SocketCluster here:

Docker volumes allow you to sneak your own directories (containing your own worker.js and broker.js source files) into the SocketCluster container without having to rebuild the image (good for development). Read this section on volumes to get an idea of how they work with Docker:

Note that if you want to attach any volumes to your SocketCluster container, you should mount them to the /usr/src/ path (inside the container) - That's the root directory from which SC loads user-defined source code.

For example, if you wanted to quickly run SocketCluster with your own workerController file (worker.js), you could just put your worker.js file inside a /home/my-username/controllers/ directory (on your host system) and then bundle it into the container as a volume by running a command like this (example):

docker run -d -v /home/my-username/controllers/:/usr/src/controllers/ -p 8000:8000 -e "SOCKETCLUSTER_WORKER_CONTROLLER=/usr/src/controllers/worker.js" socketcluster/socketcluster

To summarize:

  • The -d flag just tells Docker to run the container in the background.
  • The -v flag tells docker to mount the /home/my-username/controllers/ directory (which is on your host machine) and map it to the /usr/src/controllers/ (inside the SocketCluster container).
  • The -e flag allows you to define custom environment variables. Here we are just using the SOCKETCLUSTER_WORKER_CONTROLLER env var to tell SocketCluster to use the worker.js file which is inside the volume which we just mounted to the container at path /usr/src/controllers/.
  • The final argument socketcluster/socketcluster is the Docker image.

Contribute to SocketCluster

  • More integration test cases needed
  • Unit tests
  • Efficiency/speed - faster is better!
  • Suggestions?

To contribute; clone this repo, then cd inside it and then run npm install to install all dependencies.


If you would like to contribute to the SocketCluster project financially, you can make a Bitcoin donation to the following wallet address: 1FwhDzAAWQHtfhZkNaB7oSwmbSoreHPC6o

Change log

See GitHub releases for changes.

Custom Codecs

An increasing number of users have expressed interest in using SC to build massively multiplayer online games. One concern which was raised is that the standard SocketCluster protocol message format has too much overhead for certain kinds of games. See Based on the standard format, various actions can have between 40 and 70 bytes of overhead - This isn't much if each user is only sending one medium-sized message every few seconds but what if you wanted 10 to 20 tiny messages every second? The overhead bandwidth cost would add up and could negatively affect the profitability of the game. For this reason, we have introduced the concept of 'Custom Codecs' - Since v5.0.15, you can provide a custom Codec engine (a JavaScript/Node.js module) on both the client and server to allow you to compress messages into any format you like (optimized for your use case). If you write a Codec module which you feel might be useful for other developers, feel free to let us know here and share with the rest of the SC community.

Search for 'setCodecEngine' in!/docs/api-scserver and 'codecEngine' in!/docs/api-socketcluster-client for more details.