pub const UNAVAILABLE: &str = "UNAVAILABLE";Expand description
The service is currently unavailable. This is most likely a transient condition, which can be corrected by retrying with a backoff. Note that it is not always safe to retry non-idempotent operations.
See the guidelines above for deciding between FAILED_PRECONDITION,
ABORTED, and UNAVAILABLE.
HTTP Mapping: 503 Service Unavailable