How do I customize nginx on AWS elastic beanstalk to loadbalance Meteor?

With a LOT of help from AWS paid support, I got this working. The reality is I was not far off it was down to some SED syntaxt.

Here's what currently works (Gist):

option_settings:

  - option_name: AWS_SECRET_KEY
    value: <SOMESECRET>

  - option_name: AWS_ACCESS_KEY_ID
    value: <SOMEKEY>

  - option_name: PORT
    value: 8081

  - option_name: ROOT_URL
    value: <SOMEURL>

  - option_name: MONGO_URL
    value: <SOMEMONGOURL>

    - option_name: MONGO_OPLOG_URL
    value: <SOMEMONGOURL>

  - namespace: aws:elasticbeanstalk:container:nodejs
    option_name: ProxyServer
    value: nginx

    option_name: GzipCompression
    value: true

  - namespace: aws:elasticbeanstalk:container:nodejs:staticfiles

    option_name: /public
    value: /public

    container_commands:

  01_nginx_static:
    command: |
      sed -i '/\s*proxy_set_header\s*Connection/c \
              proxy_set_header Upgrade $http_upgrade;\
              proxy_set_header Connection "upgrade";\
        ' /tmp/deployment/config/#etc#nginx#conf.d#00_elastic_beanstalk_proxy.conf

In addition to this you need to got into your Load balancer and change the Listener from HTTP to TCP:

described here: http://docs.aws.amazon.com/elasticbeanstalk/latest/dg/using-features.managing.elb.html).