etag property

etag is used for optimistic concurrency control as a way to help prevent simultaneous updates of a instance config from overwriting each other.

It is strongly suggested that systems make use of the etag in the read-modify-write cycle to perform instance config updates in order to avoid race conditions: An etag is returned in the response which contains instance configs, and systems are expected to put that etag in the request to update instance config to ensure that their change will be applied to the same version of the instance config. If no etag is provided in the call to update instance config, then the existing instance config is overwritten blindly.