Slowing Down to Speed Up – Circuit Breakers for Slack’s CI/CD

What happens when your distributed service has challenges with stampeding herds of internal requests? How do you prevent cascading failures between internal services? How might you re-architect your workflows when naive horizontal or vertical scaling reaches their respective limits? These were the challenges facing Slack engineers during their day-to-day development workflows in 2020. Multiple internal…

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Frank Chen
•19 min read•advanced•
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Overview

This article discusses how Slack implemented orchestration-level circuit breakers to enhance developer productivity and prevent cascading failures in their CI/CD processes. By addressing challenges related to scale and complexity, Slack's engineering teams were able to improve service reliability and developer experience significantly.

What You'll Learn

1

How to implement orchestration-level circuit breakers in CI/CD systems

2

Why managing request flow is crucial to prevent cascading failures

3

When to apply load shedding and request deferral techniques

Prerequisites & Requirements

  • Understanding of CI/CD processes and orchestration
  • Familiarity with Prometheus and job scheduling systems(optional)

Key Questions Answered

How did Slack address cascading failures in their CI/CD processes?
Slack implemented orchestration-level circuit breakers that regulate request flows between services. This approach minimized cascading failures by deferring or shedding requests when dependent services were under load, thus improving overall system reliability and developer experience.
What challenges did Slack face with their CI/CD systems?
Slack faced challenges related to scaling their CI/CD systems due to increased internal requests and complexity. This led to cascading failures where one service's overload affected others, resulting in degraded performance and increased downtime for developers.
What are the key benefits of using circuit breakers in CI/CD?
The key benefits of using circuit breakers include reduced cascading failures, improved service availability, and enhanced developer productivity. By managing request flows effectively, Slack has seen zero cascading failure incidents in internal tooling over the last two years.

Key Statistics & Figures

Cascading failure incidents
Zero incidents in internal tooling over the last two years
This statistic highlights the effectiveness of the implemented circuit breakers in improving system reliability.
CI/CD request growth
10% month-over-month growth
This growth rate contributed to the challenges Slack faced, necessitating the implementation of circuit breakers.

Technologies & Tools

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Monitoring
Prometheus
Used for programmatic look-ups for dependent service metrics.
Programming Language
Hacklang
Used to implement the circuit breaker logic within Slack's CI/CD orchestration service.
Version Control
Github
Integrated with Checkpoint for CI/CD workflows.

Key Actionable Insights

1
Implement orchestration-level circuit breakers to manage request flows effectively.
This approach can significantly reduce cascading failures and improve the reliability of CI/CD systems, especially in environments experiencing rapid growth.
2
Utilize metrics from dependent services to inform circuit breaker states.
By programmatically retrieving health metrics, teams can make informed decisions about deferring or shedding requests, thus optimizing resource usage during peak loads.
3
Establish clear communication channels for circuit breaker alerts.
Automated alerts help teams respond quickly to issues, facilitating faster resolution and minimizing downtime in CI/CD workflows.

Common Pitfalls

1
Failing to monitor the health of dependent services can lead to unaddressed issues.
Without proper monitoring, teams may not be aware of service overloads, leading to cascading failures. Implementing circuit breakers requires a robust monitoring strategy to be effective.

Related Concepts

CI/CD Best Practices
Service Reliability Engineering
Load Balancing Techniques