Nginx shared cache does not respect Cache-Contol due to next.js documentation recomendation.

[l-you]

Hello. I create this discussion because I want to help people saving their time.
I spent too much time to debug this thing... So, hope it helps someone else.

I had an issue with self-hosted next.js + nginx. Cache-Control header were presented. They were public. Nginx config was very carefully configured. BUT. For some reason, Nginx did not cached any response with Cache-Control: public max-age ... immutable. It did not cache even completely static JS and CS files.
After long process of debugging I found an issue.

[l-you]

The issues was caused by the "recommendations" of the Next.js documentation.
Here is the link: https://nextjs.org/docs/app/guides/self-hosting#streaming-and-suspense .
It suggested to add header that will disable Nginx buffering to make Next.js streaming work.
But it gave much more issues and performance degradation than fixed. Every resource server from Next.js upstream server was not cached by proxy at all.
To fix that all I need is to remove the following header from my next.config.js.

	async headers() {
		return [
			{
				source: '/:path*{/}?',
				headers: [
					{
						key: 'X-Accel-Buffering', //Dissable buffering for Nginx https://nextjs.org/docs/app/guides/self-hosting#streaming-and-suspense
						value: 'no',
					},
				],
			},
		]
	},

Hope, this will save someone their time.