Sudden 5xx Spike on Web Tier

Question

Production dashboards show a sharp increase in HTTP 5xx responses from the web tier over the last 10 minutes, but traffic volume is normal. Describe your step-by-step triage and remediation.

Accepted Answer

This situation requires a methodical and rapid response to pinpoint the root cause of the 5xx errors. My first priority is to confirm the scope and impact while concurrently gathering data to inform the next steps. **1. Scope Confirmation and Initial Data Gathering:** I'd immediately verify the 5xx error rate increase across various dimensions – specific endpoints, geographical regions, or user segments if available. I'd also check related metrics like request latency to see if it's also elevated, and resource saturation (CPU, memory, network) on the web tier to rule out simple overload. Simultaneously, I'd look at our distributed tracing system for any increased error spans associated with incoming web requests. **2. Correlate with Recent Changes:** My next step is to investigate recent deployments, configuration changes, or feature flag toggles that have occurred in the last 10-15 minutes. If a correlation is found, especially with a recent web tier deployment or a change that impacts core functionality, my immediate action would be to initiate a rollback to the last known good version or disable the problematic feature flag. **3. Application and Web Server Log Analysis:** I would then dive deep into the application and web server logs (e.g., Nginx, Apache, application-specific logs) for the web tier. I'd be looking for specific error messages, stack traces, database connection issues, timeouts, or any other anomalies that coincide with the spike in 5xx responses. This often provides the most granular detail about the failure. **4. Upstream Dependency Health Check:** Since web tiers often rely on other services (databases, microservices, caches, external APIs), I'd systematically check the health and performance of these upstream dependencies. I'd look for increased error rates, latency spikes, or saturation in those services, as a failure there could be cascading and manifesting as 5xx errors in the web tier. **5. Targeted Code/Configuration Inspection and Potential Hotfix:** If logs and dependency checks don't immediately reveal the cause, I'd work with developers to quickly review recent code changes in the relevant areas of the application and web server configuration. If a clear, specific bug is identified and can be fixed with a small, targeted hotfix, I would coordinate its deployment after thorough internal testing on a staging environment, ensuring we have a rollback plan. Effective incident response hinges on robust observability. Proactive monitoring, alerting on anomalies, and well-defined runbooks are crucial for minimizing downtime and quickly restoring service. Regularly reviewing incident post-mortems helps refine our processes and prevent recurrence.

Sudden 5xx Spike on Web Tier

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