Which solution will meet these requirements?
Add another node to the ElastiCache cluster.
Increase the ElastiCache TTL value.
Change the eviction policy to randomly evict keys that have a TTL set.
Change the eviction policy to evict the least frequently used keys.
Explanations:
Adding another node can improve the capacity and potentially the cache hit ratio, but it incurs additional costs, which is against the requirement of not increasing costs.
Increasing the TTL value may allow keys to remain in the cache longer, but if the eviction policy remains unchanged, keys can still be evicted randomly. This option does not guarantee an improved cache hit ratio.
Changing the eviction policy to randomly evict keys that have a TTL set does not address the fundamental issue, as it still allows for keys without a TTL to be evicted randomly, potentially decreasing the cache hit ratio.
Changing the eviction policy to evict the least frequently used keys (LFU) prioritizes retaining more popular and frequently accessed keys, which can significantly improve the cache hit ratio without increasing costs.
I calculate that the answer is:
Change the eviction policy to evict the least frequently used keys.