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The HTML and server code remain in Next.js. Only the content of .next/static, available as _next/static, is loaded onto the CDN. Files from public require separate URLs. The behavior of assetPrefix is described in Next.js documentation.

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1. Select delivery address

General CDN: https://cdn.erlcrussia.com/YOUR_TEAM_SLUG/releases/RELEASE_ID. Custom domain: https://files.example.com/releases/RELEASE_ID after registration, DNS/TLS check. The API domain field takes the team slug or a verified hostname, without a URL scheme or release prefix.

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2. Set up a production build

next.config.js
Upload and run the same production build. After uploading the files, start Next.js with npm run start in your hosting environment. Set the custom domain in CDN_ASSET_PREFIX before building a release for that domain.

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3. Bind the user API key

Set API_BASE=https://api.erlcrussia.com. User CDN routes require erlcrussia-api-key; they do not use a master key. Keep your key out of NEXT_PUBLIC_*, HTML, and application JavaScript.

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4. Upload files before launch

For each file .next/static/RELATIVE_PATH, send a request with the path releases/RELEASE_ID/_next/static/RELATIVE_PATH:
For CSS use text/css, for fonts use MIME of the appropriate format. Do not set the generic Content-Type: multipart/form-data manually: the boundary is added by the client. compress=false saves bytes and SHA-256 assembly. For your own domain, replace domain with files.example.com. HTTP 200 returns { "success": true, "asset": { ... } }. A busy explicit path returns 409; don’t consider this a successful rewrite. Compare the SHA-256 of an existing asset or use a new RELEASE_ID. At 429, wait for Retry-After/Retry-After and retry only the rejected request. Load sequentially, taking into account the overall limit, rather than hundreds of parallel requests. Don’t download the entire .next: that’s where the server code and configuration are. Publish source maps .map only if there is a conscious need. Keep old releases as long as open tabs use them.

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5. Pictures and other public files

The regular img requests the CDN directly. When using the next/image optimization, the browser can access the local /_next/image; this is a separate mechanism. assetPrefix does not port HTML, API, Server Actions and Next.js dynamic data to CDN.

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6. Check the result

In Network, check JS/CSS/font domain, MIME, CORS and HTTP 200. Compare bytes to source files, then HEAD, Range (206) and conditional request by ETag (304). Click the interactive button: the presence of HTML does not prove the execution of JavaScript. The CDN serves files uploaded in advance. originUrl specifies a redirect destination for the domain root or a missing object, rather than a source for automatic downloads. Upload build files through the API before publishing the release. Paths starting with _next/static/ are made immutable by the CDN. If _next is preceded by a release prefix, the current implementation uses a normal Cache-Control; check the actual title. Resetting CDN does not clear the browser cache and does not itself confirm that Cloudflare has cleared it.