Postmortem: Resolving a Load Balancer Misconfiguration and Restoring Service Availability

Issue Summary:

• Duration: The outage occurred on May 10th, 2024, starting at 10:00 AM (UTC) and lasting for approximately 3 hours until 1:00 PM (UTC).
• Impact: The outage affected the availability of our primary web application, resulting in slow response times and intermittent errors for users. Approximately 30% of our user base experienced degraded performance or inability to access the service during the outage period.
• Root Cause: The root cause of the outage was identified as a misconfiguration in the load balancer settings, leading to uneven distribution of traffic and overload on certain backend servers.

Timeline:

• 10:00 AM (UTC): The issue was detected through monitoring alerts indicating increased latency and error rates on the web application.
• 10:10 AM (UTC): Engineers noticed abnormal behavior in server logs and began investigating potential causes.
• 10:30 AM (UTC): Initial assumption was that the issue was related to database performance, leading to investigation of database servers and query execution times.
• 11:00 AM (UTC): Misleading path: Database servers were optimized and scaled up, but the issue persisted.
• 11:30 AM (UTC): The incident was escalated to the infrastructure team for further investigation into network and load balancer configurations.
• 12:00 PM (UTC): Root cause identified: Load balancer misconfiguration causing uneven distribution of traffic.
• 1:00 PM (UTC): The misconfiguration was corrected, and services were restored to normal operation.

Root Cause and Resolution:

• Root Cause: The misconfiguration in the load balancer settings resulted in certain backend servers being overloaded with traffic, leading to degraded performance and errors for users.
• Resolution: The misconfiguration was corrected by adjusting the load balancer settings to evenly distribute traffic among backend servers. Additionally, monitoring and alerting thresholds were updated to detect similar issues proactively in the future.

Corrective and Preventative Measures:

• Improvements/Fixes:
• Implement automated configuration checks for load balancers to prevent misconfigurations.
• Enhance monitoring and alerting systems to detect and respond to similar issues more rapidly.
• Conduct regular audits of infrastructure configurations to identify and address potential vulnerabilities.
• Tasks to Address the Issue:
• Update load balancer configurations to ensure proper traffic distribution.
• Review and update documentation related to load balancer setup and configuration best practices.
• Conduct a post-incident review with all stakeholders to identify lessons learned and areas for improvement in incident response processes.

This postmortem outlines the duration, impact, root cause, timeline of events, and corrective/preventative measures taken in response to the outage. By addressing the root cause and implementing corrective actions, we aim to minimize the likelihood of similar incidents occurring in the future and improve the overall resilience of our systems.