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Last pushed: 2 years ago
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Dynamic Nginx Load Balancing for Docker Cloud services
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Dynamic Nginx Load Balancing for Docker Cloud
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  • All Docker Cloud services are acessible through Docker Cloud's API, this allows us to use Docker Cloud's API for service discovery.
  • When services stop, start, or scale in Docker Cloud, willrstern/docker-cloud-nginx containers will notice.
  • This allows willrstern/docker-cloud-nginx containers to dynamically load balance all services with NGINX_LB ENV variables set.

1) Docker Cloud Setup

  • Create 2 node clusters on Docker Cloud, one with the deploy tag of apps and one with the deploy tag of nginx.

As the names imply, you will give all of your apps, services, databases, etc an apps deploy tag, while only willrstern/docker-cloud-nginx containers get the nginx tag. This way, nginx will always be on the exact same IP addresses, so DNS can be assigned to those IP addresses.

  • Send all of your DNS entries & subdomains to the nginx node IP addresses.
    (NOTE: DynDNS ( supports active failover for IP addresses in case a node goes down, this is a great solution for DNS)

2) Running the Load Balancer

Run one or more copies of willrstern/docker-cloud-nginx on Docker Cloud.

  • add the nginx deploy tag & choose the every node strategy.
  • Choose the autorestart always option as well.
  • MAKE SURE to choose the Full Access API role on the Environment Variables page or the load balancer won't be able to detect running services via the Docker Cloud API.
  • Give the LB a name via the NGINX_LB_NAME=prod env variable.

The Nginx service will now listen to Docker Cloud's stream API. As services change, this LB will balance services with the NGINX_LB=prod env var. A new Nginx configuration is generated & tested with nginx -t. If Nginx accepts the new configuration, it will reload nginx.

3) Load Balancing a Service

Simply run your services on Docker Cloud with the NGINX_PORT, NGINX_VIRTUAL_HOST and NGINX_LB environment variables set in your Dockerfile:


When your service starts, willrstern/docker-cloud-nginx will notice each container and immediately reload it's config!

NOTE: Apps don't need to expose ports to be load balanced! Docker Cloud gives each container an IP, so don't add EXPOSE to your Dockerfile.

4) SSL Termination

  • create a cert
  • concatenate the .key and .crt files
  • replace newlines with \\n and copy the output

    openssl req -x509 -newkey rsa:2048 -keyout mysite.key -out mysite.crt -days 1080 -nodes -subj '/CN=*/O=My Company Name LTD./C=US'
    cat mysite.key mysite.crt > mysite.combined.crt
    awk 1 ORS='\\\\n' mysite.combined.crt
  • add the combined key & cert into NGINX_CERTS env var to your Dockerfile


If you have multiple NGINX_VIRTUAL_HOSTs, add a cert for each host with , in-between: i.e.

ENV NGINX_CERTS < key & cert>,< key & cert>


# only do SSL on
ENV NGINX_CERTS ,< key & cert>

5) Slack Integration

  • Before reloading a config, it runs nginx -t to make sure it is valid
  • If a config fails, it will continue using the last-good-config until a working config is generated
  • Add SLACK_WEBHOOK= env var to get notifications when a config fails.

Local Development Workflow

  • Set the DOCKERCLOUD_AUTH & NGINX_LB_NAME environment variables and run npm start:
    $ DOCKERCLOUD_AUTH="Basic ...." NGINX_LB_NAME=prod npm start

It will now watch your Docker Cloud cluster for events and generate a config to ./default.conf

  • How do I get the DOCKERCLOUD_AUTH variable?
    • Run any service on Docker Cloud with the Full Access API role on the environment variables page.
    • Now inspect the running service's Environment Variables tab to see the DOCKERCLOUD_AUTH value.
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