Service level - all responses to all operations in this service are cached
Operation level - all responses to this operation are cached
Response level - this response is cached
The levels are for developer convince. On the wire, all cache control is handled at the response level.
Server side
Declararative
Services or operations marked with an IdempotencyLevel in their proto will get caching automatically
Services or operations can be marked with a protobuf option communicating their desired cache eviction strategy
Imperative
Service responses programmatically tagged with cache-control metadata during service execution.
On the wire
Cache control policy is communicated to clients using standard HTTP headers on a per-message basis.
A gRPC ServerInterceptor converts cache control policy into response HTTP headers.
Cacheable service responses are marked with the following HTTP headers
Cache-Control:
max-age=xxx - the max number of seconds the response can be cached, before requiring a refresh
ETag: “ID” - a hash or version of the response used for cache re-validation
Client Side
Client-side caching handled by a client interceptor
The client specifies the maximum size of the cache in megabytes using some kind of configuration
If a cache line is expired but not yet evicted, the next request for the cached request will include an If-None-Match: xxx header, including the etag of the expired cached response
If the server's response has still not changed after cache expiration, a HTTP 304 Not Modified response with a fresh Cache-Control header will be sent in lieu of the response message, instructing the client to continue relying on its cache.
Levels of caching
The levels are for developer convince. On the wire, all cache control is handled at the response level.
Server side
On the wire
Cache control policy is communicated to clients using standard HTTP headers on a per-message basis.
Client Side