Backstage Blog

• Kotlin
• Engineering
• Types
• KotlinConf

Limiting the number of primitives we use in our code in favor of using custom types instead is an easy win. In this way, we as developers will not only reduce the possibility of bugs by using the compiler, but we will also achieve more readable and self-documented types.

• iOS
• Mobile
• Dark Mode
• Engineering
• Swift

Last week’s update to the SoundCloud iOS app includes support for Dark Mode. This took several months of work and collaboration between design and engineering teams across the company, so we wanted to share our approach to implementing Dark Mode and some of the obstacles we encountered along the way.

• Android
• Gradle
• Productivity
• Engineering
• Mobile

Part of a build engineer’s role is to speed up builds. Improving build performance and avoiding work with caching is one way to achieve this, but another tool in the build engineer’s belt is that of disallowing slow builds. This is part two in a series about solving Gradle remote build cache misses.

• Android
• Gradle
• Productivity
• Engineering
• Mobile

Until recently, one of the top technical risks facing SoundCloud’s Android team was increasing build times. Our engineering leadership was well aware of the problem, and it was highlighted in our company’s quarterly goals and objectives as modularization. Faster build times means more productive developers. More productive developers are happier and can iterate on products more quickly.

Modularization is key to decreasing build times, but avoiding work is another important part of the puzzle, and build caching is one way to avoid that work. Gradle, our tool for building Android, has a local file system cache that reuses outputs of previously performed tasks. We have been using the Gradle remote build cache in order to save our developers’ time. It helps us avoid redoing work that other teammates have already done or switching to old branches. However, to get the full benefits of caching, you have to go beyond simply setting it up.

• Android
• Mobile
• Playback
• Media

Media and playback are at the core of SoundCloud’s experience. For that reason, we have established and grown an engineering team that is specialized in providing the best possible streaming experience to our users across multiple platforms.

To do this, we combine the industry’s best-fitting solutions with our own custom technologies, libraries, and tools. In this article, let’s dive into how we improved latency in our Android application by leveraging a new engine for our player’s audio sink.

• Monitoring
• Prometheus
• SRE

If there is anything like a silver bullet for creating meaningful and actionable alerts with a high signal-to-noise ratio, it is alerting based on service-level objectives (SLOs). Fulfilling a well-defined SLO is the very definition of meeting your users’ expectations. Conversely, a certain level of service errors is OK as long as you stay within the SLO — in other words, if the SLO grants you an error budget. Burning through this error budget too quickly is the ultimate signal that some rectifying action is needed. The faster the budget is burned, the more urgent it is that engineers get involved.

This post describes how we implemented this concept at SoundCloud, enabling us to fulfill our SLOs without flooding our engineers on call with an unsustainable amount of pages.

• Web
• Playback
• TypeScript
• Streaming

Maestro is a library we have developed to handle all playback across SoundCloud web applications. It successfully handles tens of millions of plays per day across soundcloud.com, our mobile site, our widget, Chromecast, and our Xbox application. We are considering open sourcing it, and this blog post is a technical overview of what we’ve achieved thus far with Maestro.

• Announcements
• Security

We’re excited to announce the launch of our public bug bounty program with Bugcrowd — the #1 crowdsourced security platform. This public program is open to Bugcrowd’s full crowd of top, trusted whitehat hackers, and we will award up to $1,500 per vulnerability identified on our website, API, and mobile apps.

• Android
• Mobile
• Release
• Testing
• Engineering

Once every two weeks, we prepare new versions of our mobile apps to be published to the app stores. Being confident about releasing software at that scale — with as many features and code contributions as we have and while targeting a wide range of devices like we do at SoundCloud — is no easy task. So, over the last few years, we have introduced many tools and practices in our release process to aid us.

In this blog post, I’ll cover some of the techniques we use to guarantee we’re always releasing quality Android applications at SoundCloud.

• Search
• Performance
• Engineering

In the past, the Search Team at SoundCloud had high lead times for making updates to Elasticsearch clusters, either during the implementation of a new feature or simply while fixing a bug. This was because both tasks require us to reindex our catalog from scratch, which means reindexing more than 720 million users, tracks, playlists, and albums. Altogether, this process took up to one week, though there was even one scenario where it almost took one month to roll out a bug fix.

In this post, I would like to share the concrete Elasticsearch tweaks we made so that we can now reindex our entire catalog in one hour.