Postmortem Report: Service Outage
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Postmortem Report: Service Outage


This article was written as part of ALX 0x19-Postmoterm Task

Issue Summary

Duration of Outage:

- Start Time: June 5, 2024, 10:00 AM (UTC)

- End Time: June 5, 2024, 12:30 PM (UTC)

Impact:

- Service Down: Main web application was inaccessible.

- User Experience: Users encountered 503 Service Unavailable errors.

- Affected Users: 85% of total user base experienced the outage.

Root Cause:

- A misconfiguration in the load balancer led to an unexpected increase in traffic to a single server, causing it to crash.

Timeline

- 10:00 AM: Issue detected via monitoring alert indicating a spike in 503 errors.

- 10:05 AM: Engineering team alerted through automated paging system.

- 10:10 AM: Initial investigation started; assumption was a potential database issue due to similar past incidents.

- 10:25 AM: Database team confirmed no issues; attention shifted to the application servers.

- 10:40 AM: Misleading path: checked recent application code deployments but found no errors.

- 11:00 AM: Network team investigated and identified a misconfiguration in the load balancer.

- 11:15 AM: Incident escalated to the DevOps team.

- 11:30 AM: DevOps team began reconfiguring the load balancer.

- 12:00 PM: Load balancer configuration corrected and services started to recover.

- 12:30 PM: Full service restoration confirmed; monitoring continued to ensure stability.

Root Cause and Resolution

Root Cause:

The issue was traced to a recent update in the load balancer configuration. A parameter that controls traffic distribution was incorrectly set, directing the majority of incoming traffic to a single application server. This server became overwhelmed, leading to its failure and the resulting 503 errors for users.

Resolution:

The load balancer configuration was reviewed and corrected to ensure even traffic distribution across all application servers. The DevOps team implemented a rolling restart of the application servers to restore full functionality. Continuous monitoring was employed to confirm that the service was stable post-resolution.

Corrective and Preventative Measures

Improvements and Fixes:

1. Configuration Management: Review and tighten the configuration change process for critical infrastructure components such as load balancers.

2. Enhanced Monitoring: Implement more granular monitoring for load balancer configurations and traffic distribution.

3. Training: Conduct regular training sessions for the engineering and DevOps teams on best practices for configuration management and issue detection.

Specific Tasks:

1. Review Load Balancer Configuration: Conduct a comprehensive review of all load balancer settings and ensure they adhere to best practices.

2. Add Monitoring Alerts: Set up alerts for unusual traffic patterns and load balancer configurations.

3. Implement Configuration Audits: Establish regular automated audits of configuration changes for critical components.

4. Update Incident Response Plan: Revise the incident response plan to include steps for quicker identification and resolution of load balancer-related issues.

5. Documentation: Improve documentation for load balancer configurations and common troubleshooting steps.

6. Training Session: Schedule and conduct a training session focused on configuration management and monitoring.

By implementing these measures, we aim to reduce the likelihood of similar incidents and improve our response time for any future issues.

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