Following up on our previous post about team tourism at Allegro, as promised we present you with three case studies describing experiences of our engineers during their visits in other teams. The teams visited worked on content automation, machine learning and search engine optimisation.
Are you dreaming about getting a job in IT, but you feel stuck? You may be constantly working your way through books and tutorials about the technology that excites you (be it JavaScript, PHP or whatever else), but it still feels like you will never be able to get that Junior Developer position you want.
We often hear about the importance of exchanging knowledge and practices between different teams. However, less often do we hear concrete suggestions for how to do it. In this article, we discuss one of our practices to address the problem.
When we measure the page loading speed from the user’s perspective, we pay attention to the appearance of subsequent elements on the screen. Metrics such as First Contentful Paint, First Meaningful Paint and Visually Complete directly reflect what the user sees and when. But what if the page is invisible, when it loads in the background, for example in a different tab? Should we consider such views interesting for us? Don’t the collected metrics distort the results?
Developing our own A/B testing platform from scratch came with many lessons during the process. Our platform was built for people who differ vastly in terms of statistical knowledge, also for those who are not familiar with statistics at all. So the main challenge wasn’t technical implementation. The hardest thing was (and still is) developing good practices and spreading them among our users. We want to share some of our current knowledge that we think is crucial for A/B testing at scale. From this article, you will get to know about calculating sample size, what it means and what benefits it provides for you and your organization.
Reactive programming has been a hot topic on many conference talks for at least several months. It’s effortless to find simple code examples and tutorials and to apply them to greenfield projects. Things become a little bit more complicated when production services with millions of users and thousands of requests per second need to be migrated from existing solutions. In this article, I would like to discuss migration strategy from Spring Web MVC to Spring WebFlux by the example of one of the Allegro microservices. I’m going to show some common pitfalls as well as how performance metrics in production were affected by migration.
How many team leaders do you think there are at Allegro? Earlier this year, about a hundred of us had the chance to meet in person for two days. We tackled company-wide technical challenges, exchanged experiences and discussed the way we and our teams work. We encourage you to read our story since it offers a glimpse at the inner workings of our company and its culture.
After 5 years of developing and maintaining Hermes, we are very excited to announce that version 1.0 has been released.
A modern look and fully mobile-friendly design — this is how we created the new version of ads.allegro.pl. Unfortunately, several hundred tests did not protect us from errors. The last straw was when a simple but very annoying problem appeared in production. We decided to start a revolution. We considered Flow, but ended up adopting TypeScript for Allegro Ads.
This post was published on April 1st, 2019, and should not be taken too seriously.
What kind of builders do you use in your tests? Do you use the old good builders where properties are set by a withProperty method? Or maybe, you use builders that make use of closures? As soon as I joined my team, I found out that there is another approach to test builders, and it embraces maps. It seemed innovative, but after a while, it became annoying legacy code. After one of the debugging sessions, I decided to get rid of it, but the monster fought me back.
Since the beginning of my career as a Java developer, keeping up to date with Java was fairly straightforward. Big releases came every few years, causing a bit of mayhem in tooling, IDEs and job interview questions. However with each release there was a lot of time to adjust and migrate to newer versions. With Java 9 things have changed. The so called new release cadence was announced by Oracle. Instead of releasing a new major version each few years, we will get one every half year. This poses a lot of challenges to companies using Java in production, developers and the community as a whole.
We all know that “there are only two hard things in Computer Science: cache invalidation and naming things”. However, we know that writing good tests is hard, too. Does it mean that the author of the famous quote is wrong? Not necessarily! In fact, what are tests? These are descriptions of some concepts. They answer the questions: “what?”, “when?” and “how?”. When writing tests, you are answering these questions by giving names to objects, reasons, and processes. I think writing tests is hard because it is all about naming. I believe you can significantly improve your tests just by focusing on giving them correct names. Let me tell you a story of a pull request I was reviewing some time ago.
Two years ago at Allegro we used to have a very typical Big Data technology stack. The architecture was based on a Hadoop cluster and we would query it with plain Hive queries, Spark jobs and Jupyter notebooks. Over those last two years we have transformed it into a more efficient and easy to use OLAP platform.
At Allegro we use Solr as our main search engine. Due to the traffic to our search engine being thousands of requests per second and index size on the order of a hundred million documents we need to develop custom optimizations. In this post I will describe the story of our Solr plugin development.
We messed up. On July 18th, 2018, at noon, Allegro went down and was unavailable for twenty minutes. The direct cause was a special offer in which one hundred Honor 7C phones whose regular price is around PLN 850 (about € 200), were offered at a price of PLN 1 (less than € 1). This attracted more traffic than we anticipated and at the same time triggered a configuration error in the way services are scaled out. This caused the site to go down despite there being plenty of CPUs, RAM, and network capacity available in our data centers.
Lately my colleague Michał described how he tracked a Java memory leak. Although that problem was completely solved, new complications suddenly appeared on the horizon. As it usually happens, everything started with an alert from our monitoring system which woke me up in the middle of the night.
Throughout my studies at university and work in the industry I switched my primary programming language from Java to C# and back again to Java. This article gathers some of my thoughts on using both languages. It’s not intended to be a comprehensive comparison of Java and C#. There are a lot of other resources on the Internet that cover this topic. Instead, I want to focus on what I personally liked about both languages and how it felt to transition between them.
The following article has two parts. The first part describes improving Allegro iOS app launch time by adopting static linking and sums it up with a speedup analysis. The second part describes how I managed to launch a custom macOS app using not-yet-fully-released dyld3 dynamic linker and also completes with an app launch speedup analysis.
Due to the high interest and controversy concerning this blog post, we believe that it is worth adding some context on how we work and make decisions at Allegro. Each of more than 50 development teams at Allegro has the freedom to choose technologies from those supported by our PaaS. We mainly code in Java, Kotlin, Python and Golang. The point of view presented in the article results from the author’s experience.
We all make errors, but some errors seem so ridiculous we wonder how anyone, let alone we ourselves, could have done such a thing. This is, of course, easy to notice only after the fact. Below, I describe a series of such errors which we recently made in one of our applications. What makes it interesting is that initial symptoms indicated a completely different kind of problem than the one actually present.
Spring is one of the most popular JVM-targeted frameworks. One of the reasons why it has become so popular is writing tests. Even before Spring Boot era, it was easy to run an embedded Spring application in tests. With Spring Boot, it became trivial. JUnit and Spock are two most popular frameworks for writing tests. They both provide great support and integration with Spring, but until recently it was not possible to leverage Spring’s @WebMvcTest in Spock. Why does it matter? @WebMvcTest is a type of an integration test that only starts a specified slice of Spring Application and thus its execution time is significantly lower compared to full end-to-end tests. Things have changed with Spock 1.2. Let me show you, how to leverage this new feature.
At Allegro, feature velocity is a top priority. We believe that one of our critical competitive advantages is the rate at which we introduce new features. In order to achieve a high feature velocity, one of the architectural choices that Allegro made a while back was to move to microservice architecture. So when somebody uses Allegro, a request comes in (and we just have a hypothetical example here) to service D — and we can imagine a service D being a proxy or an API layer — and whatever that service is, it is not going to have all the information it needs to serve a response. So the service D is going to reach out to service C and service F, and F in turn will reach out to A, and it will in turn reach out to B and E, and you see that this very quickly gets complicated. Allegro has somewhere around 500 microservices, so you can imagine how complicated the communication map looks.
This is a post for those seeking to accomplish business goals and ensure stability of the solutions developed while maintaining focus on people. The model of three basic psychological needs that I’m presenting here may be useful for leaders, agile coaches, and scrum masters. I also encourage developers to do some self-reflection. This is the knowledge I’ve gained at the World Conference of Transactional Analysis in Berlin. Transactional Analysis (TA) is a theory of interpersonal relationships developed by Eric Berne which has a practical application in various fields, including organizations.
Application release process, or in fact software development process, as a release is the final stage of application development, is not an easy thing. Books and IT websites discuss many approaches and each has its supporters and opponents. On the one hand, you have product owners, project managers and customers who want a ready-to-use application as soon as possible. On the other hand, we developers and testers, would like to release an application of the highest quality, which may affect the delivery time. Balancing these needs is a hard nut to crack. Usually, both sides need to make some compromises to establish a common way of working. For developers and testers, it involves answering several questions concerning software development methods, skills, use of manual or automated testing, and storage of test cases and test logs. In this article I describe best practices and tips for starting a new project. I think that by following them, you will make the software development process as effective as possible and adjusted to conditions of your project.
