nginx fails to use proxy_pass when handling error - nginx

Question

I am trying to configure nginx to serve up error pages from an s3 bucket.
To that end my configuration looks like this:
location / {
error_page 404 = #fallback;
}
location #fallback {
rewrite ^ /my-s3-bucket/404.html;
proxy_pass https://s3.ap-northeast-2.amazonaws.com;
}
My expectation is that anything that hits the website and is not found is then sent to the #fallback location. I then want to rewrite the URL with the actual location of my 404 page and send on to the s3 bucket. I don't want to just 302 redirect to the 404 page.
The problem is that the proxy_pass directive is not executed. Instead, it just looks for my rewritten URL locally.
See my access logs below:
2019/01/07 03:05:42 [error] 85#85: *3 open() "/etc/nginx/html/sdfd" failed (2: No such file or directory), client: 172.17.0.1, server: www.dev.mywebsite.com.au, request: "GET /sdfd HTTP/2.0", host: "www.dev.mywebsite.com.au"
2019/01/07 03:05:42 [error] 85#85: *3 open() "/etc/nginx/html/my-s3-bucket/404.html" failed (2: No such file or directory), client: 172.17.0.1, server: www.dev.mywebsite.com.au, request: "GET /sdfd HTTP/2.0", host: "www.dev.mywebsite.com.au"
I made a request to www.dev.mywebsite.com.au/sdfd which wasn't found. 'sdfs' was rewritten to 'my-s3-bucket/404.html' but instead of then proxy passing that to https://s3.ap-northeast-2.amazonaws.com it looks for it in the local /etc/nginx/html directory.
My nginx version is 1.15.2

Answer 1

Use rewrite...break if you want the rewritten URI to be processed within the same location block. See this document for more.
For example:
location #fallback {
rewrite ^ /error/404.html break;
proxy_pass https://example.com;
}