2017-04-17

Recap of DjangoConEurope 2017

"DjangoCon, why is everybody wearing this t-shirt?" wondered the security guys in the airport of Florence, Italy, in the beginning of April. The reason for that was DjangoCon Europe 2017 happening there for a week, full of interesting talks in an exciting location.

What I liked, was that the conference was not only about technical novelties in Django world, but also about human issues that programmers deal with in everyday life.

Interesting Non-tech Topics

According to a manifest, the conference had a goal to strengthen the Django community and to shape responsible attitude towards the works done with Django.

Healthy and Successful Community

We have to build stronger communities including everyone who wants to participate without discrimination. Although, at first, it might be difficult as people have biases, i.e. prejudices for or against one person or group; by being emphatic we can accept and include everyone no matter what is their gender identity or expression, sexual orientation, ethnicity, race, neurodiversity, age, religion, disabilities, geographical location, food diversities, body size, or family status.

Valuing diversity and individual differences is the key for a healthy, positive and successful community, that empowers its members and helps them grow stronger and happier.

Responsibility for How We Use Technology

Information technology companies (Apple, Alphabet, Microsoft, Amazon, and Facebook) are among the most traded companies in the world. IT connects people and their things, automates processes, stores and treats historical data. Usually you don't need many physical resources to start an IT business. Software developers have a power to shape the future, but should use this power responsibly:

With this, great responsibility is upon us: to make the future a better place, to make the future more evenly distributed, across gender gaps and discriminations, breaking economical, political and geographical barriers.

Business

  • When creating an online business, it is important to think about the business value that your product will give to people and the way you will make money with it. Don't make assumptions without talking to your customers.
  • When choosing employees for your company, give them freedom how to prove their knowledge: by a quiz, or whiteboard interview, or a take-home programming task. Different people have different ways how to best represent their skills.
  • Launch as early as possible. Track the usage statistics with Google Analytics or other analytics service. Collect emails for the mailing list. Write about your product in a blog and personalized emails.
  • Django is an open-source project based on the hard work of many professionals, and if you gain any commercial value of it and appreciate the framework, you should donate to the Django Software Foundation.

Interesting Tech Topics

From the technical point of view, I liked several ideas mentioned in the conference:

Automate your processes

  • For starting new projects, you can have boilerplates with the mostly used functionalities already prepared. Django management command startproject has a parameter --template for that where you can pass a URL to a zip file.
  • Developers should have troubleshooting checklists for debugging, just like airplane pilots.
  • There are several types of tests. Unit tests check the functionality of individual functions or methods. Integration tests check how different units work together. The functional tests check how the processes of business requirements work from start to end. Finally, there is manual testing requiring people to click through the website and fill in the forms. Some tests like the ones involving third-party authentication or mobile phones, are hardly possible to automate. Anyway, manual testing is the most expensive in time and resources (besides it being boring for the tester), functional tests go after them, then integration tests, and lastly unit tests. Although automatic testing adds up to the development time, in the long run it makes the systems more stable and error proof.

What about Django

  • You can extend the Django ORM with custom lookups, transactions, and filtered prefetchings, to make your QuerySets more readable and more capable.
  • Once again, PostgreSQL has more capabilities than MySQL and is more stable. Use EXPLAIN ANALYZE ... SQL command to find the bottlenecks of your database queries. You can usually fix them by adding indexes.
  • You can have custom indexes for your database tables, to optimize the performance on PostgreSQL (or some other vendor) database.
  • Django 1.11 is out and it's a long-term support version.

What about Third Party Django Packages

  • After analyzing the 6 most popular model translation packages (parler, hvad, klingon, modeltranslation, nece, and i18nfield) from different angles (database support, integration in django admin and forms, performance, etc.), django-hvad seemed to be the winning approach.
  • You can visually build static websites with very little coded configuration using django-cms and djangocms-cascade. The djangocms-cascade provides an alternative nested-plugins system for Django CMS.

What about Django Projects

  • If you build web apps for developing countries, you have to keep these things in mind: people might be using cell phones instead of computers (you need responsive design with small or no images), Internet connectivity is slow and unstable (websites have to be fast and should preferably have offline versions), the users do not always understand English (the websites should be translated and adapted), and locations where people live do not always have street addresses.
  • Some interesting use cases: tracking the health of the heart with Arduino and Django, providing weather data to the whole Europe using Django, managing a radio station in Birmingham using Django.

Thanks

Finally, thanks to the organizers for making this conference as great as it was. The city was beautiful, the food and coffee was delicious, the location for the talks was impressive. Looking forward to the next DjangoConEurope!

2017-03-01

Tracking the Results of Cron Jobs

Every Django website needs some automatic background tasks to execute regularly. The outdated sessions need to be cleaned up, search index needs to be updated, some data needs to be imported from RSS feeds or APIs, backups need to be created, you name it. Usually, if not all the time, those regular tasks are being set as cron jobs. However, when some task is run in the background, by default, you don't get any feedback whether it was successfully completed, or whether it crashed on the way. In this post I will show you how I handle the results of cron jobs.

In a Django project, all those tasks are usually implemented as management commands. For each such command I write a short bash script, that will call the management command with specific parameters and will print the verbose output to a log file.

Let's say my project structure is like this on a remote server:

/home/myproject
├── bin
├── include
├── lib
├── public_html
├── backups
├── project
│   └── myproject
├── scripts
└── logs

A virtual environment is created in the home directory of myproject linux user. The Django project itself is kept under project directory. The scripts directory is for my bash scripts. And the logs directory is for the verbose output of the bash scripts.

For example, for the default clearsessions command that removes outdated sessions, I would create scripts/cleanup.sh bash script as follows:

#!/usr/bin/env bash
SECONDS=0
PROJECT_PATH=/home/myproject
CRON_LOG_FILE=${PROJECT_PATH}/logs/cleanup.log

echo "Cleaning up the database" > ${CRON_LOG_FILE}
date >> ${CRON_LOG_FILE}

cd ${PROJECT_PATH}
source bin/activate
cd project/myproject    
python manage.py clearsessions --verbosity=2 --traceback >> ${CRON_LOG_FILE}  2>&1

echo "Finished." >> ${CRON_LOG_FILE}
duration=$SECONDS
echo "$(($duration / 60)) minutes and $(($duration % 60)) seconds elapsed." >> ${CRON_LOG_FILE}

To run this command every night at 1 AM, you could create a file myproject_crontab with the following content:

MAILTO=""
00 01 * * * /home/myproject/scripts/cleanup.sh

Then register the cron jobs with:

$ crontab myproject_crontab

By such a bash script, I can track:

  • At what time the script was last executed.
  • What is the verbose output of the management command.
  • If the management command broke, what was in the traceback.
  • Whether the command finish executing or hung up.
  • How long it took to run the command.

In addition, this gives me information whether the crontab was registered and whether the cron service was running at all. As I get the total time of execution in minutes and seconds, I can decide how often I can call the cron job regularly so that it doesn't clash with another cron job.

When you have multiple Django management commands, you can group them thematically into single bash script, or you can wrap them into individual bash scripts. After putting them into the crontab, the only thing left is manually checking the logs from time to time.

If you have any suggestions how I could even improve this setup, I would be glad to hear your opinion in the comments.

Here is the Gist of the scripts in this post. To see some examples of custom Django management commands, you can check Chapter 9, Data Import and Export in my book Web Development with Django Cookbook - Second Edition.