Can Nginx limit incoming websocket message size?

Question

In the JS WebSocket library, you can limit the maximum allowed incoming message size via the maxPayload option.

I'd like to impose this limit in my Nginx reverse proxy layer, before it gets to my application server.

Does Nginx have a similar concept? Does client_max_body_size (doc) apply to incoming websocket messages?

score 1 · Accepted Answer · answered Sep 22 '20 at 19:09

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When nginx sees the 101 Switching Protocols response from the backend, it begins to treat the connection as an opaque tunnel and passes traffic back and forth without any further inspection. There is no directive that will limit any particular Websocket message in any way.

answered Sep 22 '20 at 19:09

Michael Hampton

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This is what I figured, thank you for confirming! – rynop Sep 24 '20 at 03:39

score -1 · Answer 2 · answered Sep 22 '20 at 18:57

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According to this Mattermost NGINX conf it should be possible: https://docs.mattermost.com/install/config-proxy-nginx.html

Both a websocket connection (article) and your specified client_max_body_size (doc) are used therein, so I assume it has been tested and works if they mention it in their config.

answered Sep 22 '20 at 18:57

michacassola

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There's no reason to make this assumption, and client_max_body_size doesn't work on websocket connections anyway. – Michael Hampton Sep 22 '20 at 19:08
I outlined the reason for my assumption, as a larger project uses it in their documentation. Trying to contribute... – michacassola Sep 22 '20 at 19:37

Can Nginx limit incoming websocket message size?

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