unix
11 minTCP, UDP, ss, netstat, and tcpdump: A Layered Network Debugging Guide
Diagnose connection failures by separating DNS, routing, transport, listening sockets, and application protocol behavior.
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31 matching resultsArticles and interview answers
Q&A
Q&AHow do you check whether a service is listening on a port?
Inspect local socket state and bind address before changing firewall policy.
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On Linux, `ss -lntup` lists listening sockets; `netstat` may be available via net-tools on older systems. Confirm the process, address, and network namespace. A service bound only to 127.0.0.1 is not externally reachable; also check container port mapping and host policy.
kubernetes
5 minKubernetes Foundations: Pods, Workloads, and Declarative State
Understand what the API stores, why controllers replace Pods, and how labels connect workloads without treating a cluster as a remote shell.
http
6 minHTTP conditional writes: detect an edit based on stale state
Use strong validators and atomic preconditions to prevent lost updates without confusing them with retry identity.
security
8 minCSRF defenses: reason from browser credential attachment, not CORS
Separate cross-site request forgery from cross-origin response access and validate state changes.
Q&A
Q&AHow do you safely recover a Terraform state lock after a crashed job?
Verify the lock holder is truly gone and preserve state before force-unlocking.
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Inspect lock metadata, backend state, and the pipeline that acquired it; confirm no apply is still running. Preserve a state backup and compare cloud reality before force-unlocking the specific stale lock. Then run and review a plan. Force-unlocking a live writer can permit competing state updates and corrupt tracking.
Q&A
Q&AWhy can a database trigger make an application write hard to debug?
The statement has side effects that are not visible at its call site.
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A trigger can modify other rows or tables implicitly during an insert or update. That makes the visible application statement an incomplete description of the transaction and can add locking or recursion. Document and test trigger effects, or move orchestration to an explicit routine/service when hidden behavior harms operability.
Q&A
Q&AHow do you find the third-highest distinct salary in SQL?
Use DENSE_RANK for distinct values and state whether you want salary values or employee rows.
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Filter out NULL salaries, compute DENSE_RANK() OVER (ORDER BY salary DESC), then select rank 3. DENSE_RANK treats equal salaries as the same rank. PostgreSQL, MySQL 8+, and Oracle support this window-function approach; if you instead mean the third row, use ROW_NUMBER with a deterministic tie-breaker.