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Let’s say we have a pretty standard blue/green deployment setup. NGINX is currently proxying all traffic to the live server (BLUE). We then deploy an updated version of our code to the idle server (GREEN). Finally, we refresh the NGINX configuration so that all HTTP traffic is being routed to GREEN.

From my understanding, NGINX will handle this reload gracefully. All future HTTP requests will be routed to GREEN and all pending HTTP requests that made it to BLUE will be handled by BLUE.

But what about WebSockets? Let’s say that BLUE had ten live WebSocket connections when the configuration was reloaded. What happens to them?

From my understanding on the NGINX documentation, the connections will be terminated in 60 seconds if no new data is sent.

However, if the clients are using some sort of keep-alive or ping then I’d imagine the WebSocket connections will be maintained indefinitely even though BLUE is no longer serving any other HTTP traffic.

Is my intuition right here? If so, I’d imagine that BLUE either needs to close the connections itself, or the client-side code does, unless NGINX has a feature that I am missing.

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Correct, connections will be maintained indefinitely. There's special directive to handle such cases:

https://nginx.org/en/docs/ngx_core_module.html#worker_shutdown_timeout

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