Store a Redis hash per instance, rather than a marshaled JSON string

[zcahana]

This has multiple advantages:

• It enables faster heartbeat operations - no need to read-modify-write the whole instance data (as is today) - only need to read the status and TTL, and write the last_updated + EXPIRE.
• It enables more efficient partial queries, especially when the instance metadata is large (e.g. GET /api/v1/instances?fields=service_name,endpoint,tags)
• It's more extensible and flexible

[rshriram]

Has this been resolved? @zcahana?

[zcahana]

Nope, it hasn't been touched since.