When should external caching (Redis) be added? What are the criteria?

External caching with Redis should be added when:

• There are frequently requested but rarely changing data (e.g., results of complex database queries).
• Response time is critical, and it is necessary to reduce the load on the main storage.
• The volume of data to cache exceeds the capabilities of the application's local cache.
• A shared cache is required between multiple services or application instances.

Criteria for implementing Redis:

• High frequency of repeated requests for the same data.
• Significant load on the database, which can be reduced.
• Need for quick access to data with low latency.
• Ability to cache data with an acceptable level of staleness (TTL).

Example: if you have an API that returns a list of popular products, and this list is updated once an hour, then caching in Redis will allow instant data delivery without overloading the database.