Express server not working on reverse proxy (NGINX) - node.js

Question

I am testing my express server running on proxy. My nginx config file for in sites-available is:
server {
server_name open.yousico.com;
gzip on;
gzip_proxied any;
gzip_types application/javascript application/x-javascript text/css text/javascript;
gzip_comp_level 6;
gzip_buffers 16 8k;
gzip_min_length 256;
location /_next/static/ {
alias /var/www/yousi-website/.next/static/;
expires 365d;
access_log off;
}
location / {
proxy_pass http://127.0.0.1:3000;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection 'upgrade';
proxy_set_header Host $host;
proxy_cache_bypass $http_upgrade;
}
location /api {
rewrite ^/codify(.*) $1 break;
proxy_pass "http://127.0.0.1:3001";
}
listen 443 ssl; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/open.yousico.com/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/open.yousico.com/privkey.pem; # managed by Certbot
include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
}
server {
if ($host = open.yousico.com) {
return 301 https://$host$request_uri;
} # managed by Certbot
listen 80;
server_name open.yousico.com;
return 404; # managed by Certbot
}
My server file for my express server listening on 3001 is:
const express = require('express');
const app = express();
app.listen(3001, console.log("server is running on 3001"));
app.get('/', (req, res) => {
res.send('API is running');
});
app.get('/hello', (req, res) => {
res.send('Hello World');
});
I tested this express server on my local machine, and it seems to be working fine, but when I deploy it to my cloud server, it displays "Cannot GET /api", is there something wrong with my config file? My understanding is that I set my location to /api and direct it to port 3001, and I'm sure that the server is running on 3001.

Answer 1

"Cannot XXX /YYY" is the Express default response when there is no handler for method XXX for path YYY.
In your case, I don't see an app.get("/api", ...) handler in your server code, so the error is quite warranted.
The rewrite statement in your nginx config,
rewrite ^/codify(.*) $1 break;
doesn't make sense either since there's no way for location /api to match /codify.
If you meant to strip the /api out before the URL is passed to your Express server,
rewrite ^/api(.*) $1 break;
in which case /api would be passed as /, and that would match your app.get("/")...