My First Postmortem: Outage Incident on Web Application
Published: 2024-06-09 18:11:23

Postmortem: Outage Incident on Web Application

Issue Summary: Duration: 4th June 2024, 08:00 AM — 5th June 2024, 1:00 PM (GMT) Impact: The web application experienced intermittent downtime, resulting in slow response times and partial service disruption. Approximately 35% of users were affected during this period.

Timeline:

4th June 2024, 08:15 AM (GMT): The issue was detected when monitoring alerts indicated a significant increase in response time.
The engineering team immediately started investigating the issue, suspecting a potential database problem.
Misleadingly, the investigation initially focused on the database cluster due to a recent deployment that involved schema changes.
The incident was escalated to the database administration team to assess the potential impact of the schema changes on the cluster’s performance.
Further investigation revealed no abnormalities within the database cluster, prompting the team to explore other areas of the system.
5th June 2024, 10:30 PM (GMT): The root cause was identified as an overloaded cache layer, leading to increased latency and intermittent failures.
The incident was escalated to the infrastructure team for immediate resolution.
5th June 2023, 1:00 PM (GMT): The incident was resolved, and the web application’s performance returned to normal.
Root Cause and Resolution: The root cause of the issue was an overloaded cache layer. The increased load on the system caused the cache to evict frequently accessed data, resulting in higher latency and intermittent failures. The cache’s eviction policy was not adequately configured to handle the sudden surge in traffic.

To resolve the issue, the infrastructure team adjusted the cache configuration by increasing its capacity and optimizing the eviction policy. Additionally, they implemented a monitoring system to provide early warnings when the cache utilization reaches critical levels. These measures aimed to prevent similar cache overload situations in the future.

Corrective and Preventative Measures: To improve the overall system stability, several actions will be taken:

Optimize cache eviction policies: Review and fine-tune the cache eviction policies based on usage patterns and anticipated traffic fluctuations.
Scale cache infrastructure: Evaluate the current cache infrastructure and determine if additional resources or distributed caching solutions are required to handle peak loads.
Enhance monitoring and alerts: Implement comprehensive monitoring across the entire web stack, including cache utilization, response times, and database performance, to promptly identify any anomalies.
Load testing and capacity planning: Perform regular load testing to simulate various traffic scenarios and ensure the system can handle increased loads without degrading performance.
Improve incident response process: Refine the escalation path and clearly define roles and responsibilities for incident response, ensuring efficient collaboration among teams during critical situations.
Tasks to address the issue:

Patch cache eviction policies: Adjust the cache eviction policies to prioritize frequently accessed data while considering memory constraints.
Evaluate cache infrastructure: Assess the current cache infrastructure’s capacity and explore options for scaling or introducing distributed caching.
Implement comprehensive monitoring: Deploy a monitoring solution that covers cache utilization, response times, and database performance, with appropriate alerts.
Conduct load testing: Develop and execute load testing scenarios to validate the system’s performance under varying traffic conditions.
Review and update incident response procedures: Enhance the incident response process to ensure swift identification, investigation, and resolution of future incidents.
By implementing these corrective and preventative measures, we aim to enhance the reliability and performance of our web application, reducing the likelihood and impact of similar incidents in the future.