Docker run results in "host not found in upstream" error

Question

I have a frontend-only web application hosted in Docker. The backend already exists but it has "custom IP" address, so I had to update my local /etc/hosts file to access it. So, from my local machine I am able to access the backend API without problem.

But the problem is that Docker somehow can not resolve this "custom IP", even when the host in written in the container (image?) /etc/hosts file.

When the Docker container starts up I see this error

$ docker run media-saturn:dev
2016/05/11 07:26:46 [emerg] 1#1: host not found in upstream "my-server-address.com" in /etc/nginx/sites/ms.dev.my-company.com:36
nginx: [emerg] host not found in upstream "my-server-address.com" in /etc/nginx/sites/ms.dev.my-company.com:36

I update the /etc/hosts file via command in Dockerfile, like this

# install wget
RUN  apt-get update \
  && apt-get install -y wget \
  && rm -rf /var/lib/apt/lists/*

# The trick is to add the hostname on the same line as you use it, otherwise the hosts file will get reset, since every RUN command starts a new intermediate container
# it has to be https otherwise authentification is required
RUN echo "123.45.123.45 my-server-address.com" >> /etc/hosts && wget https://my-server-address.com 

When I ssh into the machine to check the current content of /etc/hosts, the line "123.45.123.45 my-server-address.com" is indeed there.

Can anyone help me out with this? I am Docker newbee.

Answer 1

I have solved this. There are two things at play.

One is how it works locally and the other is how it works in Docker Cloud.

Local workflow

• cd into root of project, where Dockerfile is located
• build image: docker build -t media-saturn:dev .
• run the builded image: docker run -it --add-host="my-server-address.com:123.45.123.45" -p 80:80 media-saturn:dev

Docker cloud workflow

• Add extra_host directive to your Stackfile, like this

• and then click Redeploy in Docker cloud, so that changes take effect

  extra_hosts:

  • 'my-server-address.com:123.45.123.45'

Optimization tip

• ignore as many folders as possible to speed up process of sending data to docker deamon
• add .dockerignore file
• typically you want to add folders like node_modelues, bower_modules and tmp
• in my case the tmp contained about 1.3GB of small files, so ignoring it sped up the process significantly