Using Heroku to Review Static Websites

Heroku is a great platform to deploy your full-stack application. While not the appropriate place to deploy a production frontend application, Heroku’s Review Apps offer an automated mechanism to create a temporary deployment of your application to a unique, predictable URL.

Review Apps

After creating a Heroku account, create a “Pipeline” for your project and connect it to a repository on GitHub. Heroku’s Pipelines allow your application code to be deployed multiple times, from different branches.

Regardless of the technology your application uses, you will need to tell Heroku about your application’s dependencies in a manifest file. The most basic app.json will look similar to the following:

  "name": "grwifi",
  "scripts": {},
  "env": {},
  "formation": {},
  "addons": [],
  "buildpacks": []

Web Server

In order to serve up our static site, we’ll need to run a web server on Heroku. I developed sappy specifically for the purpose of serving up single-page applications (SPAs) and static websites.

To run our application on Heroku using Sappy, we’ll need to add a few files:

runtime.txt indicates that Heroku should use a Python buildpack (because Sappy is written in Python):


requrements.txt tells Heroku to install Sappy using pip (the package manager for Python):


Procfile specifies sappy as the command to run our application:

web: sappy --port=${PORT}

Automated Deployment

After adding the above files to your repository, enable Review Apps on the pipeline we created earlier:

enable review apps

When new pull requests are created on GitHub, Heroku will automatically deploy the code in that branch to a separate Heroku instance:

review app deployment

Because the temporary application deployment performs virtually identical to production, the end-to-end testing and design review that might occur later in our quality assurance process can now be performed before the code is even merged.

A working example can be found at:

See a typo? Help me edit this post.

Itemizing Your Career Goals

When I was searching for my last job, I found it useful to make a list of all the things I was looking for in a new career. As it turned out, there were actually two categories within these requirements. Upon making a list, I found that I both cared about the company I worked for and the job at hand.

I encourage everyone to make similar lists as a way to learn about your true career goals. You might be surprised that you want something different than you have. I will attempt to maintain these lists as my perspective changes, but here they are.

Company Requirements

  1. Work on new products with friends

  2. Build tools for software engineers

  3. Work in an industry that strongly interests me:
    • politics
    • music
    • theme parks
  4. Work at “a Python shop”

  5. Consult teams and companies on:
    • Automation
    • Quality Assurance
    • Testing
    • Agile Methodologies
    • DevOps
  6. Get paid to work on open source software

Job Requirements

  1. Feel like at least half of the team cares more than I do

  2. Flexible working hours and support for asynchronous work

  3. Work on a team that hates bugs and insists on prioritizing bugs first

  4. Have some free work time for side projects

  5. Have a dedicated conference budget

See a typo? Help me edit this post.

Test Coverage as a Service

Measuring coverage is an important, but sometimes forgotten part of running tests. One of the common debates is around how much coverage a project should have: 50%, 80%, 100%?

More important than the actual coverage metrics is ensuring that your coverage metrics don’t decrease when adding new code. Coverage metrics don’t tell us when a particular section of code has enough tests, but they do help inform us when a section of code has zero tests.

Tracking Metrics

A few options exist for tracking coverage metrics.

Version Control

The naive solution is to commit coverage metrics to a file in your project repository. When tests are run, check this file and report an error if coverage decreased. The main disadvantage of this approach is having lots of commits unrelated to functional changes, which adds noise to your repository.

External Services

Many external services exist to track coverage metrics. One such example is Coveralls. This service works great and is highly recommended for open-source projects to track coverage on pull requests. The main disadvantages of this service are the costs for private repositories and the inability to check coverage metrics locally.

The Coverage Space is a new RESTful API to track coverage metrics that aims to find a balance between these two options.

Basic Usage

The easiest way to get started with The Coverage Space is to use an HTTP client. HTTPie works well for this:

$ pip install HTTPie

Update metrics for your project:

$ http PUT unit=90

where my_owner/my_repo matches your project.

Check out the full API documentation at

Command-line Client

A command-line client is also available to automate the process of reading and uploading coverage metrics:

$ pip install --update

After running your tests with coverage enabled, update metrics for your project:

$ my_owner/my_repo unit

where my_owner/my_repo matches your project.

Check out the full client documentation at

See a typo? Help me edit this post.

Interested in seeing the full implementation? Check out the code on GitHub.

Tracking Direct Image Requests with Google Analytics is an open source meme generator. It renders meme images based on the requested URL.

For example, produces this image:


The site also provides an API to generate memes. This article is about the legacy implementation written using Flask and Flask API.

Client-side Analytics

I have added Google Analytics to the index and API documentation pages using the standard approach of embedding JavaScript on the page:


    ... '//','ga');
    ga('create', '<Google Analytics ID>', 'auto');
    ga('send', 'pageview');


And while this works great for HTML rendered in the browser, direct images requests (like the meme image above) go untracked.

Server-side Analytics

One solution is to track file downloads on the backend by posting to the Google Analytics API directly using an HTTP library like requests:"Sending image: %s", path)

data = dict(
    tid='<Google Analytics ID>',


)"", data=data)

return send_file(path)

While this will track page views for an image, much of the client’s information is still unavailable using this method:

  • geographic location
  • language setting
  • device properties

Tricking Clients

My complete solution involves a bit of hack to return HTML instead of an image for clients that can handle it and the normal image for those that can’t.

Visit in your browser:


It appears to be an image that can be downloaded:

$ wget
Length: 27809 (27K) [image/jpeg]
Saving to: 'or-webpage.jpg'
or-webpage.jpg 100%[============================>]  27.16K  70.7KB/s
2016-01-24 20:51:46 (70.7 KB/s) - 'or-webpage.jpg' saved [27809/27809]

But if you view the network tab in Chrome’s developer tools, you’ll see that it actually loaded a small webpage to run the same client-side Google Analytics JavaScript as above:


This was accomplished by detecting what content types the client can accept:

mimetypes = request.headers.get('Accept', "").split(',')

if 'text/html' in mimetypes:

If the client can handle HTML, the following is returned:

<!DOCTYPE html>

  <title>NOT SURE IF IMAGE / OR WEBPAGE</title>

    body {
      background-image: url("/fry/not-sure-if-image/or-webpage.jpg");
      background-repeat: no-repeat;


    ga('create', '<Google Analytics ID>', 'auto');
    ga('send', 'pageview');


This causes the browser to render the image as expected, but also run a bit of JavaScript to recored additional information about the client.

See a typo? Help me edit this post.

Interested in seeing the full implementation? Check out the code on GitHub.

Deploying a Jekyll Blog to GitHub Pages using Travis CI

Jekyll is a “blog-aware static site generator” written in Ruby that will generate a responsive website from Markdown and YAML files.

GitHub Pages offers you a free way to host static websites. And while they will automatically publish files in a repository named <your-github-id>, sometimes you need a little more control over the process.

Project Tooling

After running $ jekyll new, the base project structure will be generated for you. To simplify setup on additional machines and enable continuous deployment, I like to add additional tooling to this project.


A Gemfile is used to specify the Ruby dependencies (“Gems”) required to generate the website. In addition to jekyll, I’m using:

  • rouge - to provide syntax highlighting in code examples
  • html-proofer - to confirm that external links are valid


The Gemfile.lock is automatically generated when installing Gems. It’s purpose is to record of the exact version of each dependency the last time the project was successfully deployed.


bundler is a tool that can install and run particular versions of Gems for a project. I prefer to store the Gems locally via $ bundler install --path vendor so that I’m not polluting my system directories and can completely delete all files a project creates.


A Makefile puts everything together. I like using make (rather than rake) because it doesn’t depend on Ruby itself, does a good of tracking when files have changed, and provides a standard interface between projects.

I’ll highlight the important parts of this file. This reinstalls the dependencies whenever they change:

VENDOR_DIR := vendor

.PHONY: install
install: $(INSTALLED_FLAG)
$(INSTALLED_FLAG): Gemfile* Makefile
    bundle install --path vendor
    @ touch $(INSTALLED_FLAG)

This builds the site and validates the generated HTML:

.PHONY: build
build: install
    bundle exec jekyll build --quiet
    bundle exec htmlproof _site --only-4xx

And these targets provide a way to run the site locally:

.PHONY: run
run: install
    bundle exec jekyll serve --future --drafts

.PHONY: launch
launch: install
    eval "sleep 5; open http://localhost:4000" & make run

See the source code that generates this site as an example of how these files are used together in practice.

Developing Locally

Using the above tooling, my only system dependencies are ruby, bundler, and make. To work on a new blog entry, I simply run:

$ make launch

to bring up a local instance of the site that is regenerated whenever I edit content.

When I am done editing, running $ make ci will confirm that the site is ready to be published.

Deploying with Travis CI

Travis CI offers free continuous integration for open source projects that can be used to deploy software after running a number of checks.

Adding a .travis.yml to your project tells Travis CI how to build and deploy your site. This specifies which commands to run to install and validate each commit:

- make install

- make ci

If a new commit passes those checks, the following shell script is run:

# Generate HTML
make build ;
# Configure Git with Travis CI information
git config --global "[email protected]" ;
git config --global "travis-ci" ;
# Delete the current repository
rm -rf .git ;
# Rebuild the repository from the generated files and push to GitHub pages
cd _site ;
git init ;
git add . ;
git commit -m "Deploy Travis CI build $TRAVIS_BUILD_NUMBER to GitHub pages" ;
git push -f https://${GH_TOKEN}${TRAVIS_REPO_SLUG} main:gh-pages ;

which will publish the generated files to the gh-pages branch on GitHub.

GH_TOKEN is an encrypted access token to grant Travis CI permissions to modify files in your repository. This site provides a good overview on generating these tokens.

After deployment, you should now see your Jekyll blog live at:


See a typo? Help me edit this post.