Question

Server Sent Events Support on DigitalOcean LoadBalancers

I have an application API that works on Server-Sent Events (SSE, https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events).

It’s hosted in Managed kubernetes and exposed directly through Managed loadbalancer.

The Requests fail with “502 Bad Gateway”, “upstream connect error or disconnect/reset before headers. reset reason: protocol error”, although backend API shows 200 OK in logs.

As server-sent events are nothing but long-standing HTTP requests, there are ways to achieve it via increasing LoadBalancer <-> BackEnd SSE API HTTP connection timeout period.

I don’t see this option in DO LB though.

Ex. A workaround on GCP: https://stackoverflow.com/questions/44729212/running-a-https-sse-server-over-kubernetes-ingress-and-google-cloud-platform


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Accepted Answer

Personally Solved by using Nginx Controller.

LoadBalance <- TCP -> Nginx Controller <- HTTP with timeout -> SSE API

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
    name: sse-api
    annotations:
        kubernetes.io/ingress.class: nginx
        nginx.ingress.kubernetes.io/proxy-read-timeout: "21600"
        nginx.ingress.kubernetes.io/eventsource: "true"