SPF, DKIM and DMARC: troubleshooting email authentication
Diagnose DNS record syntax, alignment, authentication results and enforcement changes responsibly.
THE FIELD GUIDE
Troubleshooting guides and operational runbooks
Step-by-step procedures, explanations and references for infrastructure and IT operations.
✳ Review commands and environment-specific requirements before use.
Explore the library
Technical explanations with relevant tools and references.
Designing a safe deployment and rollback workflow
Use immutable releases, preflight validation, health checks and deliberate rollback verification.
Prometheus error rates and availability objectives
Calculate request error ratios from counters while accounting for labels, low traffic and reliability objectives.
PostgreSQL replication lag: what to measure
Interpret primary-side replay metrics and standby-side receive/replay timestamps without assuming one lag signal fits all.
Designing a safe Linux health-check script
Build read-only diagnostics for disk capacity, systemd services and host resources without changing state.
IPv4 subnetting: practical /31 and /32 examples
Understand prefix math, point-to-point /31 networks, /32 host routes and common allocation mistakes.
Building an incident timeline from application logs
Normalize timestamps, correlate evidence, record actions and distinguish facts from hypotheses.
HTTP security headers: what they do and do not protect
Review CSP, HSTS, nosniff, framing controls and referrer policies in deployment context.
DNS resolution versus network connectivity
Distinguish resolver failures, routing problems, port blocks and TLS issues using layered tests.
Reviewing configuration differences before deployment
Normalize and compare changes, avoid exposing secrets and create repeatable approval and rollback evidence.
Troubleshooting Cloudflare Tunnel 502, 522 and 525 errors
Learn to separate tunnel-to-origin failures from edge-to-origin connectivity and TLS handshake errors.
Apache and PHP-FPM: when HTML loads but PHP fails
A structured approach to Apache routing, FastCGI sockets, PHP handler configuration and error visibility.
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