CODEWITHSUNDEEP
node.jsexpressserver-sent-events
franmcod
franmcod

Reputation: 497

Server Sent Events Delay

Problem: Some events take 1/2 minutes to reach client.

Setup: I have a nodejs backend trying to send events using SSE to a React App client, while having nginx as a proxy. Deployed in aws with fargate task and load balancer.

The events eventually reach the client, but take alot of time making it useless for my use case.

Backend Code:

Endpoint to start connection:
handler: async (req, res) => {
  res.writeHead(200, {
    'Content-Type': 'text/event-stream',
    'Cache-Control': 'no-cache',
    'Connection': 'keep-alive'
  })
  
  const id = Date.now()
  const data = { id, response: res }
  emitterList.push(data) // array with the responses
  
  setTimeout(() => {
    res.end()
    remove(id)
  }, 2 * 60 * 1000)
  
  req.on('close', () => { remove(id) })
}

Endpoint to push data to connected clients
emitterList
  .forEach(elem => {
    try {
      console.log('WRITE: ', new Date())
      elem.response.write(`data: ${JSON.stringify(data)}`)
      elem.response.write(`\n\n`)
    } catch(err) { 
      deadEmitters.push(elem.id) 
    }
    removeDeadEmitters()

Client Code:

 const eventSource = new EventSource(`${process.env.REACT_APP_BACKEND_BASE_URL}/emitter/${id}`)
eventSource.onmessage = (e) => { console.log(new Date()) }

Is there any configuration i need to set in nginx?

Upvotes: 2

Views: 1331

Answers (1)

franmcod
franmcod

Reputation: 497

The solution was to add the header 'X-Accel-Buffering': 'no' in the response.

Upvotes: 3

Related Questions