Constant DEFAULT_MAX_BACKOFF 

pub const DEFAULT_MAX_BACKOFF: Duration;

Default maximum backoff delay (30 seconds), following Google Cloud’s recommendation. References:

• https://cloud.google.com/storage/docs/retry-strategy
• https://docs.aws.amazon.com/sdkref/latest/guide/feature-retry-behavior.html
• https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md