Lease Manager Daemon
The Lease Manager, as its name implies, is a HTCondor daemon that manages the leasing of some type of resource within the confines of a HTCondor pool. What the resource represents is immaterial to the lease manager; it could be software licenses, disk space, or network I/O. A lease manager daemon can handle one type of resource. You would configure and run a seperate lease manager for each type of resource you want to represent.
The architecture of resource leasing is very similar to the matching of machines with jobs in HTCondor. Offers of and requests for a resource are represented by classads. The ads are matched with each other, with each ad able to provide a requirements expression that constrains what it can be matched against. Resource offers are advertised in the collector by admin-provided code. The lease manager periodically queries for these ads. Clients connect to the lease manager and submit a request ad. The lease manager matches the request to one or more offers and returns the matching ad(s) to the client.
There are also some differences from the machine/job architecture. Resource requests and offers include a quantity of resource, represented by a 32-bit signed integer. An offer's resource can be shared between multiple requests, and one request can be satisfied by resources from several offers. The lease manager tracks how much of each offer's resource has been allocated, and to which requests it's been allocated. This information is persisted to disk as a classad collection.
Each allocation of resources to a request is associated with a unique id and a lease time. If the requester wishes to use the resources beyond the lease time, it must renew the lease. If the requester does not renew the lease before it expires, the lease manager will reallocate the resources to other requesters. When the requester is finished with the resources, it can return them before the lease expires to allow them to be reallocated sooner. The lease time is the minimum of the durations set by the offer, the request, and the lease manager. The lease manager can also impose a maximum lease time beyond which no renewals are allowed.
If the resources advertised by offer ads drops below the amounts allocated to requests, the lease manager will refuse to renew some of the leases so as to respect the new totals.
The lease manager responds to three commands: GET_LEASES, RENEW_LEASE, and RELEASE_LEASE. There is a DCLeaseManager class that clients can use to interact with the lease manager, which has corresponding methods. The DCLeaseManager class will return DCLeaseManagerLease objects to the client which represent the leases. It should be possible for a client to write the contents of a DCLeaseManagerLease to disk, to be read back after a failure.
The lease manager is used by some portions of stork, but isn't used anywhere in HTCondor currently. It's included in the HTCondor release. There are some tests for it in the test suite, one of which is run in the nmi build/test cycle.
Configuration parameters used by the lease manager are documented in the HTCondor manual.
- What attributes are defined for the various ads used by the lease manager?