Logic & Cloud Labs
Real-world engineering scenarios focused on infrastructure, cloud computing, debugging and incident response.
Incident 01 — API Gateway Failure
CRITICAL
At 02:14 UTC, monitoring systems detected a spike in failed requests.
[02:14:22] API Gateway online.
[02:14:31] High latency detected on auth-service.
[02:14:37] Retry threshold exceeded.
[02:14:44] JWT validation failed.
[02:14:48] Database timeout after 3000ms.
[02:14:55] Worker queue saturation detected.
[02:15:03] HTTP 500 returned to client.
[02:15:11] Automatic recovery attempt started.
Engineering Tasks
Identify which service appears to be failing first.
Analyze the relationship between JWT validation failures.
Explain worker queue saturation.
Suggest engineering actions to reduce incident impact.
Incident Resolution
What is the MOST probable root cause of the incident?
Incident 07 — Kubernetes Node Failure
HIGH
Several workloads became unavailable after one cluster node stopped responding.
Node status: NotReady
Pods unavailable
Scheduler waiting for resources
Infrastructure Investigation
What is the infrastructure impact?
Code Investigation — SQL Injection
CRITICAL
Analyze the following backend authentication code.
const query =
"SELECT * FROM users
WHERE email = '" + email + "'
AND password = '" + password + "'";
Security Analysis
What is the MOST critical vulnerability?
Code Investigation — Memory Leak
HIGH
Production memory usage increases continuously over time.
const cache = [];
app.get("/data", async () => {
const result = await fetchData();
cache.push(result);
return result;
});
Backend Analysis
What issue is MOST likely happening?
Code Investigation — Exposed Secret
CRITICAL
A Git repository containing credentials became public.
const AWS_SECRET_KEY =
"AKIAXXXXXXXXXXXXX";
Cloud Security Investigation
What is the MOST severe issue?
Incident 09 — Redis Queue Saturation
HIGH
Background jobs are delayed and message processing time increased drastically.
Redis latency exceeded threshold
Worker queue backlog increasing
Processing delay: 4800ms
Queue Investigation
What infrastructure issue is MOST likely occurring?
Incident 10 — PostgreSQL Replication Lag
CRITICAL
Users report outdated account information after recent transactions.
Replication lag exceeded 60 seconds
Replica node delayed
Read replica outdated
Database Investigation
What platform risk is MOST likely happening?
Code Investigation — Missing Error Handling
HIGH
Production API crashes during unexpected database failures.
app.get("/users", async (req,res) => {
const users =
await database.getUsers();
res.send(users);
});
Backend Stability Analysis
What engineering issue exists in this code?
Code Investigation — Blocking Operation
HIGH
The API becomes extremely slow under high traffic.
app.get("/report", (req,res) => {
const file =
fs.readFileSync("huge-report.csv");
res.send(file);
});
Performance Analysis
What is the MOST probable issue?
Incident 11 — TLS Certificate Expired
MEDIUM
Users cannot establish secure HTTPS connections to the platform.
NET::ERR_CERT_DATE_INVALID
TLS certificate expired
Secure connection rejected
Security Investigation
What impact does this MOST likely create?