Introduction

Looking for an experienced DevOps System Engineer is a challenging task, because it is usually difficult to estimate all aspects of a person's knowledge.

Technical interviews can reveal some strong and weak sides of a candidate, but sometimes they leave some open questions about real experience. And if we are talking about real routine tasks - it's not only about knowledge, but also about skills to perform different kinds of tasks using manuals, docs, and even Google.

So, the main goal of this test task - is to find out how a candidate can perform typical DevOps engineer tasks, adopting fresh-written applications to run in infrastructure and to be deployed as a production environment.

Also, this task shouldn't take more than ~4 hours.

Application

How it should look: Running Demo.

All files you need - are in this GitHub repository. Just clone it from GitHub.

This app was written in Python, and it is pretty simple. Why Python? In my own opinion, this is one of the languages that any Linux engineer should know. But this task is not about programming, so if you don't know Python and are skilled in Bash - It's ok.

Requirements:

• Python 3.6 (any other 3.x should work too)
• PostgreSQL or MySQL server
• Packages listed in requirements.txt

All this App does - counts unique visitors and shows this statistic. All it needs is a running database.

So, this app has some endpoints:

• / - main page with all data shown
• /version - JSON response with the current app version

Files description

• migrations - directory with database migrations (see Installation) based on alembic
• static - just static files for serving UI
• templates - HTML template for the main page
• app.py - main "executable" which contains all the code
• requirements.txt - list of all Python packages needed to run the app
• requirements.test.txt - list of all Python packages needed for CI/CD tasks
• version.txt - text file with the current version

Installation

To install the application, several steps should be completed:

• Prepare PostgreSQL database
• Install all required packages with pip install -r requirements.txt
• Set all required environment variables
• Apply all migrations with flask db upgrade
• Start application

For the last step, you can use different approaches - just choose one from official docs.

Configuration

As for any Docker-ready application - It can be easily configured via environment variables. So, here is a list of them:

• DATABASE_URL (required) - connection string to your database, you can find examples here.
• USER_NAME - your name, which will be shown on the page
• USER_URL - something like your personal URL (CV, blog, contact page, etc.)

Task

So, now we can talk about the goals. I'm writing just a roadmap, and any step is optional but will give additional points if is done correctly. If you are good in docs - spend more time on writing good documentation, if you have good experience in clouds - write a scalable, fault-tolerant, and cloud-ready solution. Feel free to choose your way and show your best.

An ideal solution should be fulfilled as a git repository, which will contain all Infrastructure-related code (IaC), scenarios, diagrams, and documentation as a main README.md file.

Infrastructure

I think the best option for this is Terraform. But you can also use Ansible or Chef, or any tool you want. It will be great if your solution can be used from the box to start the whole stack on a cloud provider (AWS, GCP, Azure, AlibabaCloud, etc.).

• Start all related servers/instances/logical units
• Make required changes in OS
• Install Docker (or any other kind of containerization software)

Containerisation

Dockerfile - should be included, but it isn't, because the developer of the app was too lazy for this task... So, it will be the first step to build a container with this app - writing Dockerfile and making the first docker build.

• Choose right base image
• Include all installation steps
• Make this app run and listen on an HTTP interface
• Prepare docker-compose.yml for the whole app stack, which can be used by developers

Analysis

All tools you need for this section are in the requirements.test.txt file, which can be easily used with pip install -r requirements.test.txt.

• Lintering
  • Code style
    Just use flake8 and configuration from setup.cfg
  • Static typing
    This project can be verified with mypy static types checker, configuration for it can be found in setup.cfg
• Tests
  There are not so many tests, but you can run them with pytest . and get successful results
• Code coverage
  Checkout Python Coverage project, or, you can get integration with CodeCov or Coveralls - they are free for open-source repositories.

CI/CD

At this stage you already have a project, that can be built and verified for some kind of issues. It's time to automate it.

Choose one of the CI/CD systems you like:

• GitLab
  All you need - .gitlab-ci.yml file as described here.
• BitBucket
  You can also pass this stage using BitBucket Pipelines. Just implement a build step and deployment logic somewhere, from AWS to K8s.
• Jenkins
  The most complex but also more powerful than others. If you choose it - you need to write a working Jenkinsfile to achieve the goal. I recommend using a scripted, not declarative pipeline - it would be much better to show your experience. Documentation about Jenkins Pipelines is avaiable here.

And of course, don't forget about:

• Database Migrations
  The application should execute DB migrations (as described above) on each deployment to update the schema for new code.
• Versioning
  The current project version can be seen in the file version.txt and it will be shown as the version on a web page. What about adding a build number to this version and auto-increment it on each build?

Monitoring

Just prepare some examples, of how this app could be monitored. Docker Healthchecks or rules on AWS Route53 - anything will be accepted as a solution.

Documentation

Documentation should include key points such as:

• What technologies were used and what tools are needed to use your solution?
• How to start this service from scratch using your solution?

Also, you may write additional docs like:

• How to scale the count of servers to take more load?
• What is the application deployment architecture diagram?

To draw diagrams you can use Draw.io, CloudCraft or even ASCII Art. Include them in your repository too.

Fixes?

There are some problems with app architecture. If you have a solution - it will be great!

Questions?

If you still have some questions about this task, feel free to ask me.

License

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.