Staff SRE / Principal Architect [L3] Observability Staff SRE Scenario [L3]

Q: Your company just acquired a massive monolithic C++ application built 15 years ago. It emits zero metrics and no useful logs. The developers left the company, and re-compiling the code is too dangerous. How do you gain deep observability into its network calls and database queries?

\"In an interview, I explain how we designed actionable, symptom-based alerting using the Four Golden Signals. The interviewer is testing: eBPF (Extended Berkeley Packet Filter), zero-instrumentation observability.. I structure my answer around systematic triage first, root cause analysis second, and permanent remediation third.\" Key Strategy: Pro-Tip: When you cannot modify the application code (zero-instrumentation), you use eBPF-based observability..

When you cannot modify the application code (zero-instrumentation), you use eBPF-based observability.

#Observability #Observability #L3 #Monitoring #Prometheus #SRE

🎙️ Candidate Opening & Architectural Context

""In an interview, I explain how we designed actionable, symptom-based alerting using the Four Golden Signals. The interviewer is testing: eBPF (Extended Berkeley Packet Filter), zero-instrumentation observability.. I structure my answer around systematic triage first, root cause analysis second, and permanent remediation third.""

🛠️ Production Runbook & Step-by-Step Resolution

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Production Solution & Architecture

When you cannot modify the application code (zero-instrumentation), you use eBPF-based observability. eBPF allows executing sandboxed programs directly inside the Linux kernel. Using tools like Pixie, Cilium Hubble, or Datadog Universal Service Monitoring, an eBPF agent running on the host node attaches probes to kernel-level sockets (tcp_sendmsg, tcp_recvmsg). It can intercept and parse the raw plaintext network packets (HTTP, DNS, MySQL protocols) right as they enter/leave the application, dynamically generating RED metrics (Request rates, Errors, Durations) and distributed traces for the legacy monolith without changing a single line of its original C++ code.

💡 The Senior SRE Gold Nugget (Key Architectural Takeaway)

"Pro-Tip: When you cannot modify the application code (zero-instrumentation), you use eBPF-based observability.."

⚡ 60-Second Elevator Pitch Talking Points

Immediate Triage: When you cannot modify the application code (zero-instrumentation), you use eBPF-based observab
Run targeted verification commands before modifying configuration.
Automate permanent guardrails (CI check, alerts, IaC policy) to prevent recurrence.

Q: Your company just acquired a massive monolithic C++ application built 15 years ago. It emits zero metrics and no useful logs. The developers left the company, and re-compiling the code is too dangerous. How do you gain deep observability into its network calls and database queries?

🛠️ Production Runbook & Step-by-Step Resolution

Production Solution & Architecture

📚 Related Production Scenarios in Observability