sse-cluster

sse-cluster

A scalable Server Sent Events broker

Features

• Channels

  • Seperate streams of events, they are created dynamically when the first client subscribes and are deleted automatically when the last client disconnects.

• Scalability

  • Each node uses gossip protocol to discover more nodes. New nodes need only be started with the hostname of a single active node in the cluster.
  • When a node recieves an event, it propagates it to the next node, appending metadata to the message to avoid event duplication
  • Nodes provide their HTTP port as gossip metadata, allowing connections between nodes that are configured differently from one another.

• EventSource compatibility

  • Using JavaScript, you can use native EventSource class to stream events from the broker. Below is an example:

  const channel = 'my-channel'

  // Connect to a single node, or to a load balancer in-front
  // of many nodes
  const es = new EventSource(`https://my-sse-cluster:8080/channel/${channel}`)

  // Handle the stream generically, all events will trigger this method
  es.onmessage = (e) => {
    const newElement = document.createElement('li');
    const eventList = document.getElementById('list');

    newElement.innerHTML = `message: ${e.data}`;
    eventList.appendChild(newElement);
  }

  // Handle specific event types, this method is invoked for 'ping' events.
  es.addEventListener('ping', (e) => {
    const newElement = document.createElement('li');
    const obj = JSON.parse(e.data);

    newElement.innerHTML = `ping at ${obj.time}`;
    eventList.appendChild(newElement);
  }, false);

Installation

Each node can be ran as a single binary, docker image or Kubernetes deployment.

Installing from source

This section assumes you have go 1.11+ installed.

# download the source code
go get github.com/davidsbond/sse-cluster

# install the binary
go install github.com/davidsbond/sse-cluster

# start a node
sse-cluster start

Running with docker

The application is also available as a docker image here

docker run -d davidsbond/sse-cluster start

Installing with helm

This repository also contains a helm chart for deploying to Kubernetes clusters.

helm install my-sse-cluster ./helm/sse-cluster/

Upon success, a StatefulSet and HorizontalPodAutoscaler will be created in your Kubernetes cluster that will manage the number of sse-brokering nodes. A headless service will also be created to allow name resolution of individual pods. Without this, the sse broker nodes will not be able to communicate.

Configuration

Configuration is provided to a node either via environment variables or command-line arguments. Most aspects of the broker can be controlled via these configuration values.