Openai/693d2c26-d52c-8010-af9d-5870274165bf

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gpt-5-1-thinking

User: the X-Accel-Redirect is a response header.

the X-Accel-Redirect is a response header. this means that our backed will be returning it. this is not a header that the frontend or our users send. when nginx sees this header in the response, it will look at the uri attached to it and match it to a directory we define in our nginx virtual hosts configuration file. it will then serve the file our backend specified from that directory. -- explain

Assistant: Think of X-Accel-Redirect as a secret note your backend hands to nginx saying:

Think of X-Accel-Redirect as a secret note your backend hands to nginx saying:

“Don’t send this response body. Instead, quietly go fetch that file from over there and send that to the user.”

Breaking your text down:

“the X-Accel-Redirect is a response header. this means that our backend will be returning it.”

• Your backend (app server) adds a header like: X-Accel-Redirect: /protected/files/manual.pdf
• The client never sends this header. It only comes from your backend to nginx.

“this is not a header that the frontend or our users send.”

• Correct. Browsers / frontends don’t know or care about this header.
• It’s an internal contract between your app and nginx.

“when nginx sees this header in the response, it will look at the uri attached to it and match it to a directory we define in our nginx virtual hosts configuration file.”

• In nginx config, you define special internal locations, for example: ``nginx location /protected/ { internal; alias /var/www/secret_files/; } ``
• The value of X-Accel-Redirect must match one of these locations, such as /protected/manual.pdf.

“it will then serve the file our backend specified from that directory.”

• When nginx sees X-Accel-Redirect: /protected/manual.pdf: 1. It ignores any body your backend was going to send. 2. It internally maps /protected/manual.pdf to /var/www/secret_files/manual.pdf. 3. It streams that file to the user as the response. 4. The user just sees a normal file download; they never see /protected/... and never see X-Accel-Redirect.

Why this is useful

• Your backend: - Handles authentication/authorization. - Decides which file the user is allowed to get.
• nginx: - Handles efficient file serving (large files, caching, zero-copy sendfile, etc.).

So the flow is:

1. User requests /download/123.
2. Backend checks permissions, finds it maps to /protected/manual.pdf.
3. Backend responds with headers (status 200, maybe some Content-Type, and X-Accel-Redirect: /protected/manual.pdf) and usually an empty body.
4. nginx intercepts X-Accel-Redirect, internally fetches /protected/manual.pdf from the configured directory, and streams it to the user.

Result: your app controls access, nginx does the heavy lifting of serving the actual file 🧱📂.