client_max_body_size not taking effect

Question

I am currently an application with the following components, all running in docker containers on an AWS server:

• angularJs
• nodeJS
• nginx (using jwilder/nginx-proxy image)
• letsencrypt (using jrcs/letsencrypt-nginx-proxy-companion:v1.12 image)

The application allows me to upload files from the frontend, which sends them to an API endpoint in the nodeJs backend. Multiple files can be uploaded together, and these are all base64 encoded and sent in the same request.

When the files are small (up to about 5Mb total) this works perfectly fine, but recently I've tried slightly larger files (still less than 10Mb total) and I am experiencing the following error in my Chrome browser:

{"message":"request entity too large","additionalMessage":null,"dictionaryKey":"server_errors.general_error","hiddenNotification":false,"handledError":false}

Inspecting the traffic, I realised that the request was never making it to my backend, and thus assume that this error is caused by nginx blocking the request, presumably via the client_max_body_size property in my nginx config. Checking the logs of the nginx docker container, it doesn't actually show me any errors, but does warn that a tmp file is used (note I hgave masked IPs and URLs):

nginx.1     | 2021/11/12 03:19:15 [warn] 389#389: *9 a client request body is buffered to a temporary file /var/cache/nginx/client_temp/0000000001, client: 100.00.00.000, server: my-host-url.com, request: "POST /api/docs/upload HTTP/2.0", host: "my-host-url.com", referrer: "https://my-host-url.com/"

After some googling, I found and followed this article https://learn.coderslang.com/0018-how-to-fix-error-413-request-entity-too-large-in-nginx/ which explains the issue pretty clearly and even references the same docker image that I use. Unfortunately this has not fixed the issue. I also read the nginx docs which show that this property can be applied at

http, server, location

level, and so I updated my nginx config accordingly and restarted nginx on it's own, and also shut down and restarted the containers. Still no luck :(

My docker/nginx config is as follows, noting that I am now using client_max_body_size 0; to completely disable the check instead of just increasing the size

Docker compose

version: '2.4'
    services:
        nginx-proxy:
            image: jwilder/nginx-proxy
            environment:
                # DEBUG: "true"
                DEFAULT_HOST: my-host-url.com
            ports:
                - '80:80'
                - '443:443'
            volumes:
                - /var/run/docker.sock:/tmp/docker.sock:ro
                - nginx-certs:/etc/nginx/certs:ro
                - nginx-vhost:/etc/nginx/vhost.d
                - nginx-html:/usr/share/nginx/html
                - ./nginx.conf:/etc/nginx/nginx.conf
            sysctls:
                - net.core.somaxconn=65536
            mem_limit: 200m
            labels:
                - com.github.jrcs.letsencrypt_nginx_proxy_companion.nginx_proxy
            networks:
                - common
            restart: 'always'
            logging:
                options:
                    max-size: 100m
                    max-file: '5'

    letsencrypt:
        image: jrcs/letsencrypt-nginx-proxy-companion:v1.12
        depends_on:
            - nginx-proxy
        volumes:
            - /var/run/docker.sock:/var/run/docker.sock:ro
            - nginx-certs:/etc/nginx/certs:rw
            - nginx-vhost:/etc/nginx/vhost.d
            - nginx-html:/usr/share/nginx/html
        # environment:
        #   DEBUG: "true"
        networks:
            - common
        restart: 'always'

nginx.conf copied to container

user  nginx;
worker_processes  auto;

error_log  /var/log/nginx/error.log warn;
pid        /var/run/nginx.pid;


events {
    worker_connections  1024;
}


http {
    include       /etc/nginx/mime.types;
    default_type  application/octet-stream;

    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  /var/log/nginx/access.log  main;

    sendfile        on;
    #tcp_nopush     on;

    keepalive_timeout  65;

    gzip  on;

    client_max_body_size  0;
    proxy_connect_timeout 301;
    proxy_send_timeout    301;
    proxy_read_timeout    301;
    send_timeout          301;

    include /etc/nginx/conf.d/*.conf;

    server {
        client_max_body_size  0;
    
        location / {
            client_max_body_size  0;
        }
    }
}

daemon off;