शून्य-डाउनटाइम डिप्लोयमेन्ट भनेको कुनै पनि बाधा बिना नयाँ संस्करण जारी गर्नु हो — एप्लिकेशन सम्पूर्ण डिप्लोयमेन्टको अवधिमा उपलब्ध रहन्छ। यसलाई हासिल गर्नको लागि सावधानीपूर्वक डिप्लोयमेन्ट रणनीति, पछाडिमुखी-अनुकूल परिवर्तन, स्वास्थ्य जाँच, र उड़ानमा रहेका अनुरोधको दयालु ढँगले ह्यान्डलिङ आवश्यक पर्दछ।
शून्य-डाउनटाइम के आवश्यक पर्दछ
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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 प्रविधि
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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)