Nginx not Caching my Application - node.js

Question

I'm trying to setup the caching of my ExpressApp and its rendered Jade files with Nginx.
When I have a look at the pm2 logs of my application while running the google Pagespeed Insight test, I see that the Images and HTML are still served by the app instead of the Nginx proxy.
Two Questions:
How do I have to change my configuration to have the desired effect?
How do I effectively validate that the Setup/Caching is working?
Thanks!
My current Nginx Configuration:
proxy_cache_path /var/lib/nginx/cache levels=1:2 keys_zone=backcache:8m max_size=50m;
proxy_cache_key "$scheme$request_method$host$request_uri$is_args$args";
proxy_cache_valid 200 302 10m;
proxy_cache_valid 404 1m;
server {
listen 80 default_server;
listen [::]:80 default_server;
location / {
expires 1w;
proxy_cache backcache;
#proxy_cache_bypass $http_cache_control;
add_header X-Proxy-Cache $upstream_cache_status;
proxy_pass http://localhost:3030;
}
}
Headers:
* TLS 1.2 connection using TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384
* Server certificate: ###
* Server certificate: COMODO RSA Domain Validation Secure Server CA
* Server certificate: COMODO RSA Certification Authority
* Server certificate: AddTrust External CA Root
> GET / HTTP/1.1
> Host: ###
> User-Agent: curl/7.43.0
> Accept: */*
>
< HTTP/1.1 200 OK
< Server: nginx/1.10.0 (Ubuntu)
< Date: Thu, 24 Nov 2016 13:15:37 GMT
< Content-Type: text/html; charset=utf-8
< Content-Length: 66761
< Connection: keep-alive
< Vary: Accept-Encoding
< X-Powered-By: Express
< Access-Control-Allow-Origin: *
< Access-Control-Allow-Methods: GET,PUT,POST,DELETE
< Access-Control-Allow-Headers: Origin, x-access-token, X-Requested-With, Content-Type, Accept, un-populated
< ETag: W/"104c9-8+4lo531tUk9k3SJq4sPHg"
< Expires: Thu, 01 Dec 2016 13:15:37 GMT
< Cache-Control: max-age=604800
< X-Proxy-Cache: MISS
Headers of two consecutive Requests to an Image
➜ ~ curl -I **url/img.jpg**
HTTP/1.1 200 OK
Server: nginx/1.10.0 (Ubuntu)
Date: Fri, 25 Nov 2016 03:17:02 GMT
Content-Type: application/octet-stream
Content-Length: 11007
Connection: keep-alive
X-Powered-By: Express
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: GET,PUT,POST,DELETE
Access-Control-Allow-Headers: Origin, x-access-token, X-Requested-With, Content-Type, Accept, un-populated
Accept-Ranges: bytes
Cache-Control: max-age=604800
Last-Modified: Thu, 17 Nov 2016 16:23:13 GMT
ETag: W/"2aff-158731964ca"
Expires: Fri, 02 Dec 2016 03:17:02 GMT
X-Proxy-Cache: MISS
➜ ~ curl -I **url/img.jpg**
HTTP/1.1 200 OK
Server: nginx/1.10.0 (Ubuntu)
Date: Fri, 25 Nov 2016 03:17:08 GMT
Content-Type: application/octet-stream
Content-Length: 11007
Connection: keep-alive
X-Powered-By: Express
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: GET,PUT,POST,DELETE
Access-Control-Allow-Headers: Origin, x-access-token, X-Requested-With, Content-Type, Accept, un-populated
Accept-Ranges: bytes
Cache-Control: max-age=604800
Last-Modified: Thu, 17 Nov 2016 16:23:13 GMT
ETag: W/"2aff-158731964ca"
Expires: Fri, 02 Dec 2016 03:17:08 GMT
X-Proxy-Cache: MISS

Answer 1

The headers you show as the request headers are most probably not the original ones, because it says "Provisional headers shown".
The actual request headers probably contain the "cache-control" header and your nginx configuration uses that header to bypass the cache, as indicated by the 'X-Proxy-Cache:BYPASS' response header.
If there is no reason to keep it, you should remove the proxy_cache_bypass-directive from your config.