Lease.md

Overview

The Lease interface provides methods to grant, revoke, and keepalive leases.

grant function

1. The function build leaseGrantRequest with ttl value (unit seconds).
2. It call respond gRPC interface with leaseGrantRequest to build a new lease in etcd.

revoke function

1. The function build leaseRevokeRequest with lease id.
2. It call respond gRPC interface with leaseRevokeRequest to revoke respond lease.

startKeepAliveService function

1. The function will start a background scheduler keepAliveSchedule to send keep alive request for lease registered to Lease Client.
2. It will open a StreamObserver to etcd, send request to this StreamObserver can keep the lease alive.
3. It will new a ScheduledExecutorService to run keepAliveExecutor and deadLineExecutor periodically.

closeKeepAliveService function

1. This function will end the background scheduler.
2. It will close the StreamObserver to etcd.

setLeaseHandler function

1. This function set LeaseHandler for the lease.
2. The LeaseHandler interface:
   • onKeepAliveRespond
     • It will be called when the receive lease response from etcd.
   • onLeaseExpired
     • It will be called when the lease expire and removed from etcd.
   • onError
     • It will be called when some exception occurred.

keepAlive function

1. It will create a keepAlive Object, and keep the lease alive.
2. It will add the created keepAlive object to the keepAlives map.
3. It will set handler for the keepAlive.
4. The background scheduler will send keep alive requests for the added keepAlive when it approaches to the nextKeepAliveTime.

keepAliveExecutor function

1. This function is called periodically by keepAliveSchedule.
2. The lease may expire as:
   • The etcd respond overtime.
   • The client fails to send request in time.
3. It will scan the keepAlives map and find the leases that requires keepAlive requests to send based on its nextKeepAliveTime.
4. Send request to the StreamObserver for these leases.

deadLineExecutor function

1. This function is called periodically by keepAliveSchedule.
2. It will scan the keepAlives map and find the leases that requires removed from the map based on its DeadLine.
3. call the on onLeaseExpired method for these leases.

processKeepAliveRespond function

1. It will get the keepAlive instance based on the leaseID.
2. if ttl < 0, it remove respond keepAlive from keepAlives map and call onLeaseExpired.
3. else it reset the keepAlive's nextKeepAliveTime and deadLine value.

keepAliveResponseStreamObserver interface instance

1. The StreamObserver is the stream etcd uses to send responses.
2. The gRPC client calls onNext when etcd server delivers a response.
3. The onNext function will call processKeepAliveRespond.