How do you scale a Django application horizontally, and what state must move out of the app servers? Django एप्लिकेशन को हॉरिज़ॉन्टली कैसे स्केल करें, और कौन-सी स्टेट को ऐप सर्वर्स से बाहर ले जाना चाहिए?

Horizontal scaling means running multiple identical Django application instances behind a load balancer instead of making one server bigger, allowing traffic to be distributed and instances to be added or removed based on load. For this to work correctly, application servers must be stateless — any request could be routed to any instance, so nothing critical can be stored only in one instance's local memory or disk.

This means sessions must be stored in a shared backend (database or Redis, not the default local-memory cache backend) rather than per-instance memory, uploaded media files must go to shared object storage (S3 or equivalent) rather than local disk, and any in-process cache must be replaced with a shared cache like Redis so all instances see consistent cached data. Sticky sessions at the load balancer are sometimes used as a workaround but reintroduce the same scaling and failover problems statelessness is meant to avoid.

SESSION_ENGINE = 'django.contrib.sessions.backends.cache'
CACHES = {'default': {'BACKEND': 'django_redis.cache.RedisCache', 'LOCATION': 'redis://redis:6379/1'}}
DEFAULT_FILE_STORAGE = 'storages.backends.s3boto3.S3Boto3Storage'