Mar 4 2015
Any website finds identification of visitors crucial.
Usually, cookie files are used, but they have several drawbacks,
as users can delete or block them (e.g. by activating the “incognito” mode in web browsers).
Besides, cookies fail to identify a user who uses several different web browsers, even if he or she connects using the same device.
Hence the idea of a browser fingerprint — a unique user identifier
which does not change between successive sessions and which does not depend on selected web browser.
Mar 2 2015
Typically, applications we develop gain more and more features in each sprint. After a certain time it’s hard to say how
a particular functionality should work. No one remembers all the corner cases without looking into the source code. So
we write high level acceptance tests that describe expected behavior. Using some example scenarios that the end user
could trigger, tests check that the outcome is correct. After the user story is implemented, the test joins a
regression suite that will protect the application from bugs
introduced in future stories.
Feb 26 2015
This post is an introduction to sysdig — an “open source, system-level exploration” tool that ease
the task of performance troubleshooting in Linux operating system.
Feb 23 2015
According to what we were taught at school, you cannot build a perpetual motion machine as it is against
the laws of thermodynamics. There is nothing in the world that can generate energy forever, without any energy
source. Anyway, I am not going to teach you physics. Instead, I would like to write about the energy that drives us.
Feb 18 2015
There’s no denying that the most important way
to reach an offer on Allegro is a search bar. How it works from the user’s point of view everybody knows. You input a
search phrase, select some filters when needed, click “search” and you get some results, usually quite fast. What looks
like a simple and straightforward process on the surface, inside actually engages really
complicated algorithms. In this first post of the series we will try to make you a little bit familiar with the tools we
use here at Allegro to make search happen. In an upcoming post, we will describe how to use them, focusing mainly on the
analysis process.
Feb 13 2015
On January 30th we made a visit to GeeCon TDD to find out what’s going on in the world of TDD. Allegro was one of the sponsors
of the event and our colleague Piotr Betkier appeared as a speaker. The theme of the conference was the broad subject of
software testing and TDD. The question for the conference to answer was “Is TDD dead?”. The major stars who came to Poznań
were Nat Pryce and Steve Freeman, authors of the book “Growing Object-oriented Software, Guided by Tests”.
Feb 11 2015
Allegro was founded in 1999. As you can imagine, technology was quite different at that time.
Small startup of three developers wrote first version of the platform. There was no problem with scalability as there
were only hundreds of users. We didn’t even used any sql database. All data were stored in the files. This first few
years of Allegro are all almost mythical for current developers as no code or data schema is preserved from these
times. Over all those years we have grown up – a small company hiring a few programmers has changed into a
corporation with dozens of teams and hundreds of programmers. Everything was much easier back then when people were,
literally, working together. But with the growing number of programmers, we faced problems that soon turned into
blockers. Our code and its complexity grew along with the company. After some time, we realized that such uncontrolled
growth would block us one day. Application maintenance would become expensive, and any change of the system
behaviour would be risky. That is why we decided to act and our today’s architecture is the result of that decision.
Here is the story of our transition.
Feb 6 2015
Even though a lot of software development is high-level stuff which does not require the developer to delve into the details of how things
work under the hood, in certain situations it can be very helpful to know what sort of low-level operations an application is performing.
Two typical scenarios are performance tuning and debugging.
Feb 3 2015
In this post I would like to show you how to add a resource programatically in Jersey
container. We start from a business use case that needs to be implemented. What we are
trying to achieve is to allow external clients to use some resources of internal
microservices. I am aware of the fact that the solution we are going to discuss is not
the best way to solve the problem. Choosing the best solution lies outside the scope
of this post. What is covered in this post are the steps and solutions we tried to use
in order to solve the problem.
Jan 29 2015
When you publish your service API it is crucial to make it easy to upgrade. If you forget about it, you might end up in dependency hell.
Each attempt to change your API will force you to contact all your clients and tell them to upgrade their software.
As a result, both you and your clients will be very unhappy.
You can mitigate it by providing multiple versions of your resources. But there is no single way how to manage them.
Different companies solve it in different ways. Below you find three most popular approaches.
Jan 26 2015
This is the second part of the article about how, in one of the teams at Allegro Group,
we combined the Minimum Viable Product (MVP) and Walking Skeleton concepts
with the Story Mapping technique to quickly define the scope of the forthcoming project
and eventually built a reliable and valuable product in a limited amount of time.
Jan 21 2015
Any programmer can admit that working with code that has been developed for years by many people is a difficult task.
Keeping your own application architecture clean is troublesome, and it gets even more challenging in case of an application
that was written by other programmers several years ago. One can enjoy writing new applications and tools that do
not carry any burden, but each product evolves together with its business assumptions. Moreover, new features are added
and the application needs to be constantly improved.
Jan 16 2015
QCon is one of the most identifiable conferences in IT world. Several times every year it connects IT professionals
from the whole world in such a well-known locations like San Francisco, New York, Shanghai, Tokyo, Beijing or London.
The main idea of conference is to facilitate the spread of knowledge and innovation in developer community.
Jan 14 2015
At the beginning of December we published our first post about Swift.
Today we want to continue the Swift thread and introduce a few interesting facts about functions in Swift language.
Jan 7 2015
On 23rd and 24th October, the Allegro platform suffered a failure of a subsystem
responsible for asynchronous distributed task processing. The subsystem consists
of several daemon processes, Gearman job server,
Redis and Oracle databases. The problem affected many areas,
e.g. features such as purchasing numerous offers via cart and bulk offer editing
(including price list editing) did not work at all.
Moreover, it partially failed to send daily newsletter with new offers.
Also some parts of internal administration panel were affected.
Dec 31 2014
Devoxx (formerly JavaPolis) is an annual Java-centric conference organized by BeJUG that
takes place in Antwerp, Belgium. Such a big Java event can‘t go unnoticed by Allegro. This year five representatives
of our company had a chance to experience five full days of Devoxx.
Dec 24 2014
This post is an introduction to the mysterious and alien world of aspect-oriented programming, or aspects for short.
At first sight it is difficult to understand why to use aspects and how a project can benefit from this technology.
The simplest use case where we can use an aspect is logging. I believe that everyone saw, or even wrote on their own,
a piece of code where the business logic was interweaving with infrastructure code:
Dec 19 2014
In distributed environments it is crucial to have a common, standardized language which services can use to exchange
information between each other. At Allegro, to meet this goal, we’ve chosen the REST architecture.
Dec 17 2014
Big Data Spain is an annual conference on Big Data and related topics held in the
suburbs of Madrid. This year’s, i.e. third, edition has so far been the biggest; it has attracted more than 500 guests
and various speakers including Big Data celebrities like Paco Nathan of Databricks. During two days of the conference,
guests could attend many keynotes, speeches and workshops and learn about variuos products, services and specific
use-cases, in both English and Spanish. Allegro was represented by two employees with a presentation on Hadoop pitfalls
and gotchas.
Dec 12 2014
Two weeks ago, I attended Swift Warsaw as a speaker, holding a presentation on “Swift Runtime
— Swift Method Dispatching”. I promised to summarise the talk in an article, so hereby I keep my promise.
Dec 9 2014
This post is about migrating a real-world, non-trivial, business-critical application from Java 7 to Java 8.
When searching for a JDK 8 migration guide, you can often find blog posts that claim to be helpful but in reality only repeat the list
of features found in release notes and offer no insight into issues you may encounter in practice. Having no migration guide during our own
migration, we decided to create one. This is a report right from the trenches, no details spared, casualties included.
Dec 5 2014
At Allegro, we always try to pick the right tool for the job. As a result, despite focusing on JVM for implementing our
services, we do use Python extensively for infrastructure automation and management.
Dec 3 2014
Introduction of Swift programming language during WWDC 2014 was big news in developers’ world. The community
warmly welcomed the language created by Apple and many developers started learning and using it immediately.
This article explains what Swift is and its basic concepts. If you are an iOS (or OS X) developer it means that you probably already know all the
things described below, but if you haven’t started your iOS development adventure yet (but you want to), this article could be a good introduction for you.
Dec 2 2014
Two weeks ago we attended AWS re:invent conference in Las Vegas.
Our company was represented by Wojciech Lesicki (Product Owner of our cloud infrastructure), Sebastian Pietrowski (Head of Architecture and Operations) and Mateusz Gajewski (Solutions Architect).
This post summarises new product announcements made during the keynotes, our impressions on breakout sessions, bootcamps and conference itself.
Nov 26 2014
REST (Representational State Transfer) has become very popular
over the course of the past few years. It has happened so not only because of growing popularity of lightweight Web frameworks
(like Angular.js) but also due to the new Microservice Architecture
hype (thank you Netlifx). Frameworks like Spring add new REST-related functionalities with
each new release and more and more companies decide to give them a try… But how do you test them - REST services and their clients?
