Zero-downtime deployment म्हणजे नवीन आवृत्त्या रिलीज करणे बिना वापरकर्त्यांना कोणताही व्यत्यय आणले — अनुप्रयोग संपूर्ण दरम्यान उपलब्ध राहतो. हे साध्य करण्यासाठी सावधान डिप्लॉयमेंट धोरणे, मागे-सुसंगत बदल, आरोग्य तपास, आणि उड्डाणातील विनंत्यांचे शिष्टाचारी हाताळणी आवश्यक आहे.
Zero-downtime साठी काय आवश्यक आहे
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GOAL: deploy a new version with NO user-facing downtime (always-available service):
→ never take the whole service offline to deploy
→ always have healthy instances serving while updating others
→ handle in-flight requests gracefully (don't drop them mid-request)
→ Combine several techniques (below).
मुख्य तंत्रे
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✓ DEPLOYMENT STRATEGY — rolling, blue-green, or canary (never all-at-once downtime):
→ rolling: update instances gradually (others keep serving)
→ blue-green: switch traffic to the new environment instantly
✓ LOAD BALANCER + HEALTH CHECKS → route traffic only to healthy/ready instances;
new instances join only when READY (readiness checks)
✓ GRACEFUL SHUTDOWN → draining: stop sending new requests to an instance, let it FINISH
in-flight requests, THEN stop it (handle SIGTERM) → no dropped requests
✓ BACKWARD-COMPATIBLE changes → old and new versions coexist during the rollout
(API and DATABASE compatibility — expand-contract migrations)