sse-cluster

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.

Argument	Environment Variable	Description	Default
`gossip.port`	`GOSSIP_PORT`	The port to use for communications via gossip protocol	`N/A`
`gossip.hosts`	`GOSSIP_HOSTS`	The initial hosts the node should connect to, should be a comma-seperated string of hosts	`N/A`
`gossip.secretKey`	`GOSSIP_SECRET_KEY`	The key used to initialize the primary encryption key in a keyring	`N/A`
`http.client.timeout`	`HTTP_CLIENT_TIMEOUT`	The time limit for HTTP requests made by the client	`10s`
`http.server.port`	`HTTP_SERVER_PORT`	The port to use for listening to HTTP requests	`8080`
`http.server.cors.enabled`	`HTTP_SERVER_ENABLE_CORS`	If set, allows cross-origin requests on HTTP endpoints	`false`

imladenovic / sse-cluster