War Stories interview prep

• A Deployment That Could Not Be Rolled Back — A database migration included in the same deployment as application code made rollback impossible after the ne
• A Failed Migration That Left the Database in a Partial State — A migration script that added 3 constraints failed partway through, leaving the database with one constraint a
• A Feature Flag Change That Triggered a Production Outage — Enabling a feature flag caused all application instances to immediately reload configuration, creating a thund
• Accidental DELETE Without a WHERE Clause in Production — An engineer running a cleanup script against the wrong environment deleted 2.3 million user preference records
• An IAM Misconfiguration That Let a Developer Become Admin — A developer with iam:PassRole and lambda:CreateFunction permissions silently escalated to full AdministratorAc
• AWS Credentials Committed to a Public GitHub Repository — An access key ID and secret committed in a config file were found by an automated scanner within 4 minutes, le
• Backups That Were Never Actually Completing — A 14-month-old backup job was logging success but writing zero bytes — discovered only when a recovery was att
• BGP Route Leak That Rerouted Traffic Through an Unexpected AS — A misconfigured BGP peer accepted a broader-than-intended prefix announcement, briefly rerouting user traffic
• Blue-Green Deployment That Resulted in Split-Brain Sessions — Incomplete session store migration meant users were authenticated on green but not on blue, causing random log
• Cache Stampede on a Flash-Sale Product Page — Synchronized TTL expiry on a high-traffic product page caused every application server to hit the database sim
• Connection Pool Exhaustion That Brought Down 12 Microservices — A single slow migration caused connection pool exhaustion on the RDS primary, cascading to 12 services that sh
• DynamoDB Hot Partition That Throttled a Flash Sale — A product ID used as the DynamoDB partition key concentrated 80% of flash-sale reads on a single partition, ca
• Failover to a Lagging Replica Lost 4 Minutes of Orders — Automatic RDS failover promoted a replica that was 4 minutes behind the primary, discarding all writes from th
• Internal DNS Cache Poisoning That Redirected API Traffic — A misconfigured internal DNS resolver accepted forged responses, causing microservice-to-microservice calls to
• Malicious npm Package Exfiltrated Environment Variables at Build Time — A typosquatted npm package installed via a developer's local npm install exfiltrated AWS credentials from CI e
• N+1 Query Pattern That Collapsed Under Load — An ORM-generated N+1 query pattern that ran fine in staging (10 records) caused 8,400 database queries per use
• NAT Gateway Port Exhaustion Under Bursty Lambda Traffic — A burst of Lambda invocations exhausted NAT Gateway SNAT ports, causing connection failures to external APIs w
• Node.js Memory Leak That Required Daily Restarts — A closures-based event listener accumulation caused heap growth of 40 MB/hour, requiring nightly automated res
• Public S3 Bucket Exposed Customer PII for 8 Months — A single Block Public Access setting left unchecked exposed 3.2 million customer records in a logging bucket.
• Silent Data Corruption from an Off-By-One Migration — A database migration that ran successfully corrupted currency amounts for 6% of transactions due to an integer
• Single-Region Dependency That Caused a Global Outage — A globally deployed service collapsed because its auth token endpoint was pinned to a single AWS region.
• The Cascade That Took Down Three Services — A single slow dependency turned synchronous timeouts into a process-pool meltdown that propagated upstream.
• Third-Party API Outage That Was Mistaken for Own Code — Four hours of debugging internal code before realizing the root cause was a third-party geolocation API silent
• Thundering Herd After a Cache Cluster Restart — Restarting an ElastiCache cluster during low-traffic hours triggered a database overload at 3 AM when all cach
• TLS Certificate Expiry That Took Down an Internal API — A wildcard TLS certificate for internal APIs expired with no automated renewal, causing all internal service-t

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