Solution:
Root Cause: Node.js Framework Body-Parser Limits When Nginx proxies request streams to Node.js, Nginx passes requests up to
client_max_body_size. However, frameworks like Express.js default to a
100kb limit via internal middleware (
body-parser). If exceeded, Express responds with its own HTTP 413 error payload (
PayloadTooLargeError: request entity too large).
Diagnostic Verification: Examine Node.js application process logs:
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bash
pm2 logs --lines 50
# or
journalctl -u my-node-app.service -n 50
Look for
PayloadTooLargeError: request entity too large stack traces.
Step-by-Step Fix: 1 Update Express middleware body-parsing definitions in your application entry point (server.js or app.js):
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javascript
const express = require('express');
const app = express();
// Increase JSON payload limits
app.use(express.json({ limit: '50mb' }));
// Increase URL-encoded payload limits
app.use(express.urlencoded({ limit: '50mb', extended: true }));2 If using file upload middleware (e.g., express-fileupload or multer):
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javascript
const fileUpload = require('express-fileupload');
app.use(fileUpload({
limits: { fileSize: 50 * 1024 * 1024 }, // 50MB
}));3 In your Nginx reverse proxy configuration, align client_max_body_size:
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nginx
location /api/ {
proxy_pass [http://127.0.0.1:3000](http://127.0.0.1:3000);
client_max_body_size 50M;
}4 Restart the Node application and reload Nginx:
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bash
pm2 restart all
sudo systemctl reload nginxPrevention & Long-Term Monitoring: Explicitly define explicit middleware limit exceptions on dynamic upload routes instead of blanket high payload thresholds.