Q: A Lambda function times out on every invocation. What could be the cause?
1. Timeout too short — default is 3 seconds. If the function takes 5 seconds, increase the timeout (up to 15 minutes).
#AWS #ECS, EKS, Lambda #L2 #Cloud #Infrastructure #S3
🎙️ Candidate Opening & Architectural Context
""AWS reliability requires differentiating between AWS control plane limits and host-level resource exhaustion. When addressing this question, I walk the interviewer through our production incident runbook: isolating the blast radius, checking diagnostic logs and metrics, and applying a safe fix.""
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🛠️ Production Runbook & Step-by-Step Resolution
1️⃣
Initial Diagnostics & Root Cause Analysis
- Timeout too short — default is 3 seconds. If the function takes 5 seconds, increase the timeout (up to 15 minutes).
- Waiting on external resources — DB connection takes too long, external HTTP call is slow, S3 download is large.
- Cold start latency — VPC Lambda cold starts can add 5-10 seconds for ENI provisioning. Use provisioned concurrency for latency-sensitive functions.
- VPC connectivity issue — Lambda in VPC can't reach the internet or RDS because of missing NAT Gateway or incorrect Security Group rules.
2️⃣
Remediation & Permanent Safeguards
Execute the resolution runbook and verify workload health:
- Infinite loop or deadlock — the function logic has a bug that never resolves.
- DB connection pool exhausted — Lambda opens a new DB connection per invocation. With high concurrency, you exhaust DB connections. Use RDS Proxy to pool connections.
💡 The Senior SRE Gold Nugget (Key Architectural Takeaway)
"Pro-Tip: Timeout too short — default is 3 seconds. If the function takes 5 seconds, increase the timeout (up to 15 minutes).."
⚡ 60-Second Elevator Pitch Talking Points
- Timeout too short — default is 3 seconds. If the function takes 5 seconds, increase the timeout (...
- Waiting on external resources — DB connection takes too long, external HTTP call is slow, S3 down...
- Cold start latency — VPC Lambda cold starts can add 5-10 seconds for ENI provisioning. Use provis...
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