What caused the sudden spike in API latency for Twilio Segment's Event Streaming service yesterday afternoon?

Introduction

The sudden spike in API latency for Twilio Segment's Event Streaming service yesterday afternoon is a critical issue that demands immediate attention and thorough analysis. As we delve into this problem, we'll follow a systematic approach to identify, validate, and address the root cause while considering both short-term fixes and long-term implications for our product ecosystem.

Step 1

Clarifying Questions (3 minutes)

• Looking at the timing, I'm thinking this might be related to a recent deployment. Has there been any significant code push or infrastructure change in the last 24-48 hours?

Why it matters: Recent changes often correlate with performance issues. Expected answer: Yes, there was a deployment yesterday morning. Impact on approach: If confirmed, we'd focus on changes in that deployment.

• Considering the nature of Event Streaming, I'm curious about the volume of data. Has there been an unusual spike in data volume or user activity preceding the latency issue?

Why it matters: Unexpected load can strain systems and cause latency. Expected answer: Data volume has been within normal ranges. Impact on approach: If true, we'd look more at system issues rather than capacity problems.

• Given that it's an API latency issue, I'm wondering about the scope. Is this affecting all API endpoints or specific ones?

Why it matters: Helps narrow down the problem area and potential causes. Expected answer: The issue is primarily affecting data ingestion endpoints. Impact on approach: We'd focus our investigation on the ingestion pipeline and related components.

• Thinking about our monitoring systems, I'm curious if there were any alerts or anomalies detected before the latency spike became apparent?

Why it matters: Early warning signs can provide valuable clues about the root cause. Expected answer: There were some minor CPU utilization alerts an hour before the spike. Impact on approach: We'd investigate the correlation between CPU usage and the latency issue.