Building with AWS S3

Docker builds are supported in two ways. First is to set build: to a git or HTTP URL that is compatible with the using the Docker Remote API. The second approach is to set build: to a local directory and the build context will be uploaded to S3 and then built on demand on each node.


  • Docker
  • Rancher Compose
  • AWS account
  • Rancher Server running with 1 Host

In our example, we’ll define our application in the docker-compose.yml and place the file in a composetest directory. The compose file defines a service called web, that opens port 5000 of the container to be exposed on the host. There is also a link to a service called redis. The application running inside the web container will also be able to reach the redis container by its hostname redis.

version: '2'
    build: .
      - "5000:5000"
      - redis

    image: redis

We’ll also add a rancher-compose.yml file to the same composetest directory to be able use the scale attribute for Rancher. By default, if there is no rancher-compose.yml file or the service is not defined, the scale of the service will be one container.

version: '2'
    scale: 3

Once the files are set for Rancher Compose, the next step is to write the application itself and steps to build it.

Using the example from the docker-compose documentation, we’ll create a filed named The application talks to a host called redis, which is expected to be running a redis KV store. It increments the value of a key in the store called hits and retrieves it.

from flask import Flask
from redis import Redis

app = Flask(__name__)
redis = Redis(host='redis', port=6379)

def hello():
    return 'Hello World! I have been seen %s times.' % redis.get('hits')

if __name__ == "__main__":"", debug=True)

The application is dependent on two libraries, so we will also create a file called requirements.txt.


Now, let’s define the steps to build the application using a Dockerfile. Inside the Dockerfile, the instruction define how the application container should be built.

FROM python:2.7
ADD . /code
RUN pip install -r requirements.txt
CMD python

Since you already have Rancher server running, you need to set up your AWS credentials and just run Rancher Compose with your Rancher server URL and API key.

# Set up your AWS credentials
$ aws configure
AWS Secret Access Key []: AWS_SECRET_KEY
Default region name []: NOT_NEEDED_FOR_S3
Default output format [None]:
# Run rancher-compose in your composetest directory where all the files are created
$ rancher-compose --url URL_of_Rancher --access-key username_of_API_key --secret-key password_of_API_key up

With the command, the web container should be started on a host in your Rancher server. It will first upload the current directory to S3, which can be verified by going to S3 UI and checking for a new upload. After the image is uploaded, it will download it to the host and build a container using the files that were provided.

Troubleshooting S3 Builds

If you are having issues with your S3 builds, you can test out your builds in Docker to make sure that your image can be built and the container can run. In the same location as you’d run your Rancher Compose command, use the following commands to test if it would work in Docker.

# Test building locally to see if works
$ docker build -t test .
# Test running the newly built image
$ docker run test