seaworthy-demo

A demo of Seaworthy for my Docker/Travis blog part 3

This repository is split into three directories:

1. django: All the Django project code and its Dockerfile
2. nginx: The Nginx configuration and Dockerfile
3. seaworthy: The Seaworthy test code

Running the demo

Pull all the necessary images (optional—Seaworthy will quietly do this for you if you don't):

docker pull jamiehewland/seaworthy-demo:django
docker pull jamiehewland/seaworthy-demo:nginx
docker pull postgres:alpine

Install Seaworthy (you probably want to be in a virtualenv):

cd seaworthy
pip install -r requirements.txt

Run pytest:

pytest -v test.py

Debugging

To access the Django web app, insert a breakpoint into a test that uses the Nginx container, for example:

     def test_admin_page(self, nginx_container, django_container):
         """
         When we try to access a page served by Django, for example, the Django
         admin page, that page is returned via Nginx.
         """
+        import pdb;pdb.set_trace()
         client = nginx_container.http_client()
         response = client.get("/admin")

Run pytest again for the test:

pytest -v test.py::TestNginxContainer::test_admin_page

You should (eventually) get at a Python debugger shell from which you can inspect the containers in scope:

collected 1 item

test.py::TestNginxContainer::test_admin_page
>>>>>>>>>>>>>>>>>>>>>> PDB set_trace (IO-capturing turned off) >>>>>>>>>>>>>>>>>>>>>>>
> /Users/jamie/ws/seaworthy-demo/seaworthy/test.py(39)test_admin_page()
-> client = nginx_container.http_client()
(Pdb)

Here you can do cool things like inspect the Nginx container for its port:

(Pdb) nginx_container.get_first_host_port()
('127.0.0.1', '32805')

And then go to http://127.0.0.1:32805/icecream in your browser:

Note that you can also pass the --pdb option to pytest to jump to the Python debugger when a test fails.

Architecture

The Nginx container (1) receives incoming HTTP requests and proxies them to the web application container (2). The web application container in the centre contains the actual application: Django served using Gunicorn. This Django application needs a database to store its data in, and that’s where the final part comes in — the PostgreSQL database container (3).

The two volumes are Docker volumes that are shared between the Nginx and web application containers. The “socket volume” contains Gunicorn’s Unix socket. Nginx initiates HTTP requests to Gunicorn & Django via this socket. The second volume is used to share Django’s static files with Nginx, which Nginx can serve to users efficiently.