Continuous Integration

The Practice

 every push to main (and every PR):
 1. build compiles + artifacts construct
 2. test suites run (unit → integration slices)
 3. static analysis: lint, type-check, security scan
 4. artifact PUBLISHED with immutable version tag

 [git push]──►[CI pipeline]──►✓ green: merge/deploy-eligible
                            └─✗ red: block, notify, fix-forward

 the contract: MAIN IS ALWAYS RELEASABLE.
 integration pain gets paid in tiny increments continuously
 instead of as a big-bang merge catastrophe quarterly.

What Separates Real CI From Ritual

 □ SPEED BUDGET: pipleline ≤ ~10min for PRs. slower = devs
   batch commits = integration risk returns through the back door.
   parallelize; cache aggressively; tier suites (fast on PR,
   deep nightly)
 □ DETERMINISM: flaky tests are poison — quarantine + fix
   discipline, never "re-run until green" culture
 □ ARTIFACT IMMUTABILITY: build once, promote the SAME
   artifact through environments (never rebuild per env —
   "tested ≠ deployed" drift dies here)
 □ EVERYTHING IN REPO: pipeline-as-code, reviewed like code
 □ FAIL LOUD: broken main is an incident-class event;
   revert-first culture over debug-on-main culture

Pipeline Anatomy That Scales

Stage	Contents	Budget
pre-flight	lint/format/typecheck	<2 min
unit	fast tests, high coverage	<5 min
build+scan	artifact, SBOM, CVE scan	parallel
integration slice	container deps, key paths	<10 min
nightly	full suites, perf smoke, e2e sample	unhurried

 monorepo note: affected-detection ("which services did this
 change touch?") keeps CI proportional to change size —
 otherwise monorepos drown everyone in everyone's builds.

The Payoff Chain

 CI is unglamorous but load-bearing:

 CI ✓ → deployable anytime → CD becomes possible
      → trunk-based development viable
      → feature flags carry releases (not branches)
      → rollbacks are boring (small deltas since last good)

 skip CI rigor and every downstream practice degrades into
 ceremony: deploys become events, branches fossilize,
 releases turn heroic. the boring foundation IS the strategy.

Interview Framing

“How do you keep 30 services integrable?” scored shape: always-releasable-main contract stated, speed-budget + flaky-quarantine disciplines named, build-once-promote-artifact rule emphasized, monorepo affected-detection mentioned if relevant. CI questions grade whether you see pipelines as ENGINEERING CULTURE infrastructure rather than a YAML afterthought.