Technical guide
What is the difference between git add -A and git add .?
In modern Git, both stage additions, modifications, and deletions. Their path scope differs when you run them from a subdirectory.
Explainer
Use a different Prometheus scrape URL for each target
Configure target labels, paths, schemes, and query parameters with separate jobs or target relabeling.
Explainer
Prometheus rate() vs. increase()
Understand per-second counter rates, window increases, reset handling, and why an estimated count can be fractional.
Explainer
Collect Docker application logs with Filebeat and Logstash
Configure a filestream container parser, send events to Logstash, and handle multiline records before different container streams are combined.
Explainer
Reassemble multiline Docker logs in Fluentd
Use concat with an explicit event boundary, container-and-stream isolation, timeout routing, and deliberate timestamp behavior.
Technical guide
Does every subdomain need a separate TLS certificate?
Choose separate, wildcard, or multi-domain certificates, with the SAN matching rules and renewal trade-offs that determine coverage.
Technical guide
Fetch and check out a specific Git tag
Fetch a Git tag, make a shallow clone or source archive, preserve detached commits, and verify the revision used for deployment.
Explainer
Fix Elasticsearch “No handler for type [keyword]”
Check the Elasticsearch version and mapping structure before correcting a keyword mapping error on an older cluster.
Explainer
Supply Fluentd environment variables in systemd and containers
Use environment-backed Fluentd settings with explicit defaults, systemd overrides, Docker env files, Kubernetes Secrets, and safe validation.
Technical guide
Fix ERR_SSL_VERSION_OR_CIPHER_MISMATCH
Diagnose failed TLS negotiation, missing CDN edge coverage, and outdated protocol settings without confusing them with certificate-name errors.
Technical guide
Diagnose OpenSSL “ASN1_CHECK_TLEN: wrong tag”
Check the object type and encoding before treating an ASN.1 parsing error as a damaged certificate.
Technical guide
Fix Cloudflare error 526: invalid SSL certificate
Check the origin certificate behind Cloudflare, distinguish Origin CA trust from public trust, and restore Full (strict) validation.