Nginx client_max_body_size not working in Docker container on AWS Elastic Beanstalk

It turns out that AWS uses nginx to proxy connections to the docker container, it's necessary to update the AWS nginx configuration in order to set client_max_body_size. Note that I am using 64bit Amazon Linux 2014.09 v1.0.9 running Docker 1.2.0.

I needed to create .ebextensions/01-client-max-body.config with the contents below.

The important line is "server 127.0.0.1:EB_CONFIG_NGINX_UPSTREAM_PORT;"

files:
  "/tmp/custom-nginx.conf":
    mode: "00644"
    owner: "root"
    group: "root"
    content: |
      upstream docker {
        server 127.0.0.1:EB_CONFIG_NGINX_UPSTREAM_PORT;
        keepalive 256;
      }

      server {
        listen EB_CONFIG_HTTP_PORT;
        client_max_body_size 10M;

        location / {
          proxy_pass      http://docker;
          proxy_http_version      1.1;
          proxy_set_header Host                $host;
          proxy_set_header X-Real-IP           $remote_addr;
          proxy_set_header X-Forwarded-For     $proxy_add_x_forwarded_for;
        }
      }

container_commands:
  01_remove_orig_config:
    command: 'sed -i ''/EOF/,/EOF/d'' /opt/elasticbeanstalk/hooks/appdeploy/enact/00flip.sh '
  02_add_new_conf:
    command: 'sed -i ''/# set up nginx/a sed -i s\/EB_CONFIG_NGINX_UPSTREAM_PORT\/$EB_CONFIG_NGINX_UPSTREAM_PORT\/ \/tmp\/custom-nginx.conf \nsed -i s\/EB_CONFIG_HTTP_PORT\/$EB_CONFIG_HTTP_PORT\/ \/tmp\/custom-nginx.conf \ncat \/tmp\/custom-nginx.conf > \/etc\/nginx\/sites-available\/elasticbeanstalk-nginx-docker.conf'' /opt/elasticbeanstalk/hooks/appdeploy/enact/00flip.sh'
    test: 'test ! $(grep custom-nginx.conf /opt/elasticbeanstalk/hooks/appdeploy/enact/00flip.sh)'

Answer provided by super helpful AWS support..

The accepted answer didn't work for me, but I managed to figure it out.

Previously I used a prebuilt docker image (hosted in my own registry), and specified access and url in the dockerrun.aws.json file, and then had a config file at .elasticbeanstalk/config.json with the following:

deploy:
  artifact: Dockerrun.aws.json

This uploaded only the dockerrun file as an artifact.

In order to set the client_max_body_size via ebextentions, you must switch to either uploading the entire folder via eb deploy or specify a zip file artifact containing your .ebextentions folder

I then had success with a config file at .ebextentions/size.config containing:

files:
  /etc/nginx/conf.d/proxy.conf:
    content: |
      client_max_body_size 50M;
container_commands:
   01_reload_nginx:
     command: "service nginx reload"

I arrived at this answer thanks to https://stackoverflow.com/a/23587371/2653503, https://stackoverflow.com/a/39829789/2653503, and a few others that I can't find right now.