You can use S3 for this, no? (Admittedly it's clunkier than a service with SDKs.)
LIST, GET, and PUT are strongly consistent, the file name is the lock name, write the owner id and expiry timestamp in the file, and periodically extend the lock expiry (heartbeat). If an other process finds an expired lock delete the file.
LIST, GET, and PUT are strongly consistent, the file name is the lock name, write the owner id and expiry timestamp in the file, and periodically extend the lock expiry (heartbeat). If an other process finds an expired lock delete the file.