The cache will be stored in Instance store volume then what will happen if its get restarted ?

If an instance with cache stored in instance store volume is restarted or stopped, all data in the cache is lost, because instance store volumes are ephemeral and do not persist after reboot or termination

Does Memcached allows Read Replica ?

No, Memcached does not support Read Replicas.
Only Redis in ElastiCache supports replication and failover for high availablity

What is Cache Invalidation ?

Cache Invalidation is the process of removing or updating outdated data in the cache to ensure it matches the latest data in the main database

What are the caching techniques available ?

Write through
Write back
Read through
Lazy loading

What is Cache Hit and Miss meaning ?

A Cache Hit occurs when the requested data is found in the cache, providing a fast response.
A Cache Miss happens when the data is not in the cache, so it must be fetched from the main database or source