Getting started with Wercker and Python

This guide is a step-by-step approach to developing, building and deploying a sample app with Wercker within minutes.

While this guide uses Python, the general concepts explained in this tutorial apply to every other programming language.

Requirements

To be able to follow along with this guide, you will need the following things:

  • A Wercker account
  • The Wercker CLI

Setting up the app

Before we can start developing, we have to fork and clone the sample app into our local development environment. After you’ve done that, cd into the project directory:

$ cd getting-started-python/

Next, install the dependencies using pip and finally run the app to verify everything is working:

$ pip install -r requirements.txt
$ python app.py

Now in your browser navigate to localhost:5000/cities.json and you should be presented with the following output:

{"cities" : ["Amsterdam","Berlin","New York","San Francisco","Tokyo"]}

Developing the app

Now that we’ve setup our app we can start developing. Our list of cities is a bit short, so why not add another one in there? Before we do that however, let’s first take a look at the wercker.yml file included in your project folder.

Wercker.yml

The wercker.yml is the only config file you need for using Wercker. In it, you will define all your steps needed to successfully develop, build and deploy your application. To get started, we’re only interested in developing our app. Let’s take a closer look at this top of the file:

# The container definition we want to use for developing our app
box:
  id: python:2.7-slim
  ports:
    - "5000"

This initial box section defines two things. The id property states which container image you want to use for your project; as we’re developing in Python for this sample we’ve chosen the python:2.7-slim image. Container images are retrieved from Docker Hub if no other registry is specified. You can read more about containers here. The ports property specifies the ports that you want your running container to expose. This example only requires a single port but you can specify multiple ports here if required.

Now let’s look at the dev section:

# Defining the dev pipeline
dev:
  steps:
    # first we want to run pip-install to install all the dependencies
    - pip-install
    # then we want to run a wercker step that watches your files and reloads
    # when changes are detected.
    - internal/watch:
        code: python app.py
        reload: true

This is where we define what we want to happen in our development pipeline, which in this case are two steps: pip-install and internal/watch. Theinternal/watch step watches your files for changes, and if reload is set to true it restarts your app so your changes are reflected immediately. This is especially useful for when you’re developing webapps, as we’re doing now. Both of these steps are pre-written bash scripts written by either wercker or the community. You can read more about steps here.

Let’s see these steps in action now and fire up our dev pipeline.

Wercker dev

In your project folder, run wercker dev –expose-ports. You should see something similar to the following output:

--> Executing pipeline
--> Running step: setup environment
Pulling from library/python: 2.7-slim
Digest: sha256:8ad54c658f70c4265fc41f1ef997c796836d738e32562f0b13afe331b5b7916c
Status: Image is up to date for python:2.7-slim
--> Copying source to container
--> Running step: wercker-init
--> Running step: pip-install
No virtual environment detected. Sudo will be used for pip install
Running pip install with sudo: sudo pip install -r requirements.txt
Collecting Flask==0.9 (from -r requirements.txt (line 1))
 Downloading Flask-0.9.tar.gz (481kB)
Collecting Werkzeug>=0.7 (from Flask==0.9->-r requirements.txt (line 1))
 Downloading Werkzeug-0.12.2-py2.py3-none-any.whl (312kB)
Collecting Jinja2>=2.4 (from Flask==0.9->-r requirements.txt (line 1))
 Downloading Jinja2-2.9.6-py2.py3-none-any.whl (340kB)
Collecting MarkupSafe>=0.23 (from Jinja2>=2.4->Flask==0.9->-r requirements.txt (line 1))
 Downloading MarkupSafe-1.0.tar.gz
Building wheels for collected packages: Flask, MarkupSafe
 Running setup.py bdist_wheel for Flask: started
 Running setup.py bdist_wheel for Flask: finished with status 'done'
 Stored in directory: /root/.cache/pip/wheels/61/5d/75/1ab0ce251600e89ea376ac9e6e344e672ee2c09e089223b72d
 Running setup.py bdist_wheel for MarkupSafe: started
 Running setup.py bdist_wheel for MarkupSafe: finished with status 'done'
 Stored in directory: /root/.cache/pip/wheels/88/a7/30/e39a54a87bcbe25308fa3ca64e8ddc75d9b3e5afa21ee32d57
Successfully built Flask MarkupSafe
Installing collected packages: Werkzeug, MarkupSafe, Jinja2, Flask
Successfully installed Flask-0.9 Jinja2-2.9.6 MarkupSafe-1.0 Werkzeug-0.12.2
pip install succeeded
--> Running step: watch
--> Reloading on file changes
--> Reloading
 * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
 * Restarting with stat

Wercker first checks out your code and then sets up the container environment. This means that the container will be pulled from Docker Hub and subsequently started with access to your checked out code. It will then start executing all the steps that are defined in the wercker.yml.

If you navigate once again to localhost:5000/cities.json you should see the same output as before. That’s not very exciting, so let’s see our live reloading in action. In app.py:14 add a new city to the array:

data = {"cities" : ["Amsterdam","Berlin","New York","San Francisco","Tokyo","London"]}

Once you save your changes, the app should automatically reload. If you refresh your page, our new city should be there! Hurrah!

There are many more steps to use for developing your app. Take a look around, and if you can’t find the step you’re looking for, you can always just make your own

Now that we’re done developing, we want to push our changes and let wercker build and deploy our app for us.

Building your app

Before we continue, Let’s revisit our wercker.yml again.

box:
  id: python:2.7-slim
  ports:
    - "5000"

dev:
  steps:
    - pip-install
    - internal/watch:
        code: python app.py
        reload: true

build:
  steps:
    - pip-install
    - script:
        name: python unit test
        code: |
          python app_test.py

Build Pipeline

We’re now interested in what’s happening in the build pipeline. Notice that the - pip-install step remains the same, but we’ve added a new kind of step: a script step. This script step is a piece of inline bash code which we’re using to run our tests.

- script:
    name: python unit test
    code: |
      python app_test.py

This is a simple inline bash script. You can create these steps directly in your wercker.yml or share them with the community by submitting a step to our repository. This script simply runs the unit tests using python.

Wercker build

Now that we have a better understanding of our wercker.yml let’s go ahead and let wercker build our project. In your project folder, run

$ wercker build
--> Executing pipeline
--> Running step: setup environment
Pulling repository python
Pulling image (2.7-slim) from python: 8320d6315882
Pulling image (2.7-slim) from python, endpoint: https://registry-1.docker.io/v1/: 8320d6315882
Pulling dependent layers: 8320d6315882
Download complete: 8320d6315882
(...)
Download complete: 8320d6315882
Status: Image is up to date for python:2.7-slim
--> Running step: wercker-init
--> Running step: pip-install
No virtual environment detected. Sudo will be used for pip install
Running pip install with sudo: sudo pip install  -r requirements.txt
Collecting Flask==0.9 (from -r requirements.txt (line 1))
  Downloading Flask-0.9.tar.gz (481kB)
Collecting Werkzeug>=0.7 (from Flask==0.9->-r requirements.txt (line 1))
  Downloading Werkzeug-0.10.4-py2.py3-none-any.whl (293kB)
Collecting Jinja2>=2.4 (from Flask==0.9->-r requirements.txt (line 1))
  Downloading Jinja2-2.7.3.tar.gz (378kB)
Collecting markupsafe (from Jinja2>=2.4->Flask==0.9->-r requirements.txt (line 1))
  Downloading MarkupSafe-0.23.tar.gz
Installing collected packages: Werkzeug, markupsafe, Jinja2, Flask
  Running setup.py install for markupsafe
  Running setup.py install for Jinja2
  Running setup.py install for Flask
Successfully installed Flask-0.9 Jinja2-2.7.3 Werkzeug-0.10.4 markupsafe-0.23
pip install succeeded
--> Running step: python unit test
F
======================================================================
FAIL: test_index (__main__.CitiesTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "app_test.py", line 12, in test_index
    self.assertEqual(response.data, json.dumps(['Amsterdam', 'San Francisco', 'Berlin', 'New York']))
AssertionError: '["Amsterdam", "San Francisco", "Berlin", "New York", "Tokyo"]' != '["Amsterdam", "San Francisco", "Berlin", "New York"]'

----------------------------------------------------------------------
Ran 1 test in 0.008s

FAILED (failures=1)
--> Step failed: python unit test
--> Pipeline failed
It seems like our test is failing because we added a new city that isn’t reflected in the tests. Go ahead and add our new city to app_test.py and run the wercker buildagain.

self.assertEqual(response.data, json.dumps(['Amsterdam', 'San Francisco', 'Berlin', 'New York', 'Tokyo']))
It should give you the following output:

pip install succeeded
--> Running step: python unit test
.
----------------------------------------------------------------------
Ran 1 test in 0.007s

OK
--> Steps passed
--> Pipeline finished
Success!

Building locally is very useful when you’re not sure your code will run because of some changes you made. As such you don’t want to push these changes to your Git provider just yet.

But since we’ve verified that our app is compiling and running correctly, it’s time to let wercker build & deploy your app in the cloud, which is what we’ll be doing in the next section.

Adding your app to Wercker

The next step is to create a new application on wercker. Head over to https://app.wercker.com/ and select Add application from the top menu bar.

Select the Owner and Git Provider

First we have to choose who owns the app. For this tutorial, go ahead and select yourself. If you prefer, you can select an organization you created on wercker.

Now select GitHub as your Git provider (BitBucket and GitLab are also available), and then click Next.

Select the repository

You now see a list of your existing repositories. Select the Python example you forked earlier from the list and click Next.

Configure Access

The next step is about configuring access, and the first option wercker will check out the code without using an SSH key is fine for the purpose of this tutorial, because it’s an open source and public application. So go ahead and click Next.

Review application details

Finally, once you’ve verified all the settings, click Create to complete setting up our app. Now you can trigger the first build!

Triggering your first build

The Nicely Done! screen gives you the option to generate a wercker.yml file. But as the repository already contains one, all you have to do is click trigger a build now .

The Runs page now shows a new build has been triggered! This build will do the exact same as the one you triggered locally but now everyone in your team can see and comment on the build.

Wrapping up

Congratulations! You’ve built your first app using Wercker.