Postmortem: Removing all users from github.com/trivago

When was the last time you booked accommodation without checking its photos? Most probably never! Because having imagery information makes our decision-making process much easier and faster. However, picking up the best possible images of a hotel to show to the user is an interesting problem to solve, because it can be a naive random selection or a sophisticated machine learning model to know what the user truly wants at that moment.

When operating applications in Kubernetes, proper lifecycle management is crucial to enable Kubernetes to manage applications correctly throughout their different phases: startup, runtime and shutdown. Improper or incomplete lifecycle management can lead to incidents with unforeseen and difficult to debug application behavior, such as random CrashLoopBackOffs, broken/zombie services not being restarted or even entire services not becoming healthy after a scheduled restart. Based on both good and bad applied practices in trivago’s search backend, this article outlines key aspects for lifecycle management of our Java applications running inside docker containers on Kubernetes.

Five years ago trivago started to build guilds – small communities dedicated to certain topics or technologies – as a need arose to organize the collaboration of more than a hundred developers on a wide range of topics. You can read more about how we started in the previous blog posts Part I and Part II. A lot has changed about trivago as an organisation as well as about the technologies we use for product development since our engineers started organising the first tech guilds years ago.

When techies hear about email marketing and designing HTML emails, they typically roll their eyes and think of a very boring field of work. In this article, we hopefully can explain to you why this is wrong from our perspective. Our team built a solution that our marketers use to easily design HTML emails with predefined modules within our email marketing platform Salesforce Email Studio, which is part of the Salesforce Marketing Cloud (SFMC).

This article presents how trivago’s search backend team used reactive programming in Java effectively when designing and implementing one of our many Java backend services. Compared to traditional imperative and functional programming, reactive programming requires a mindset-shift in order to apply the concepts and techniques effectively. The benefits we gain support us in some key challenges that every engineer is facing with essentially every (micro-) service in today’s backend architectures: handling of blocking IO, backpressure, managing highly varying loads as well as message and error propagation.

In the trivago backend, we use the reactive programming pattern for fetching prices from advertisers and updating our caches. This helps us to increase the responsiveness (i.e., scalability and resilience) of our backend. Thus, our backend system can alleviate high response times from internal components and our advertisers while staying responsive, even if downstream components fail entirely. Here is how we use the Java library Reactor Core to ensure those guarantees: