Spectrum LSF multi-cluster Models and Configurations

IBM® Spectrum LSF (formerly IBM® Platform™ LSF®) is a complete workload management solution for demanding HPC environments. Featuring intelligent, policy-driven scheduling and easy to use interfaces for job and workflow management, it helps organizations to improve competitiveness by accelerating research and design while controlling costs through superior resource utilization.

Without a scheduler, an HPC Cluster would just be a bunch of servers with different jobs interfering with each other. When you have a large clusters and multiple users, each user doesn’t know which compute nodes and CPU cores to use, nor how much resources are available on each node. To solve this, cluster batch control systems are used to manage jobs on the system using HPC Schedulers. They are essential for sequentially queuing jobs, assigning priorities, distributing, parallelizing, suspending, killing or otherwise controlling jobs cluster-wide. Spectrum LSF is a  powerful workload management platform, job scheduler, for distributed high performance computing.

Computational multi-clusters are an important emerging class of supercomputing architectures. As multi-cluster systems become more prevalent, techniques for efficiently exploiting these resources become increasingly significant. A critical aspect of exploiting these resources is the challenge of scheduling. In order to maximize job throughput, multi-cluster schedulers must simultaneously leverage the collective computational resources of each of its participating clusters. By doing so, jobs that would otherwise wait for nodes to become available on a single cluster can potentially run earlier by aggregating disjoint resources throughout the multi-cluster. This procedure can result in dramatic reductions in queue waiting times.

Organizations  might have multiple LSF clusters manged by different business units. In this scenario it is good to share the resources across the cluster to reap the benefits of global load sharing.

• Ease of administration 
• Different geographic locations 
• Scalability

There are two Spectrum LSF  Multi-cluster Models :

Job forwarding Model:

In this model, the cluster that is starving for resources sends jobs over to the cluster that has resources to spare. To work together, two clusters must set up compatible send-jobs and receive-jobs queues.

With this model, scheduling of MultiCluster jobs is a process with two scheduling phases: the submission cluster selects a suitable remote receive-jobs queue, and forwards the job to it; then the execution cluster selects a suitable host and dispatches the job to it. This method automatically favors local hosts; a MultiCluster send-jobs queue always attempts to find a suitable local host before considering a receive-jobs queue in another cluster.

You could refer another blog for configuring your cluster to Job forwarding Mode. Click here.

Resource leasing model

In this model, the cluster that is starving for resources takes resources away from the cluster that has resources to spare. To work together, the provider cluster must “export” resources to the consumer, and the consumer cluster must configure a queue to use those resources. In this model, each cluster schedules work on a single system image, which includes both borrowed hosts and local hosts.

Two clusters agree that one cluster will borrow resources from the other, taking control of the resources. Both clusters must change their configuration to make this possible, and the arrangement, called a “lease”, does not expire, although it might change due to changes in the cluster configuration.

With this model, scheduling of jobs is always done by a single cluster. When a queue is configured to run jobs on borrowed hosts, LSF schedules jobs as if the borrowed hosts actually belonged to the cluster.

1. Setup:
   • A resource provider cluster “exports” hosts, and specifies the clusters that will use the resources on these hosts.
   • A resource consumer cluster configures a queue with a host list that includes the borrowed hosts.
2. To establish a lease:
   1. Configure two clusters properly (the provider cluster must export the resources, and the consumer cluster must have a queue that requests remote resources).
   2. Start up the clusters.
   3. In the consumer cluster, submit jobs to the queue that requests remote resource.
   4. At this point, a lease is established that gives the consumer cluster control of 
            the remote resources.
   • If the provider did not export the resources requested by the consumer, there is no lease. The provider continues to use its own resources as usual, and the consumer cannot use any resources from the provider.
   • If the consumer did not request the resources exported to it, there is no lease. However, when entire hosts are exported the provider cannot use resources that it has exported, so neither cluster can use the resources; they will be wasted.
3. Changes to the lease:
   • The lease does not expire. To modify or cancel the lease, you should change the export policy in the provider cluster.
   • If you export a group of workstations allowing LSF to automatically select the hosts for you, these hosts do not change until the lease is modified. However, if the original lease could not include the requested number of hosts, LSF can automatically update the lease to add hosts that become available later on.
   • If the configuration changes and some resources are no longer exported, jobs from the consumer cluster that have already started to run using those resources will be killed and requeued automatically.
   If LSF selects the hosts to export, and the new export policy allows some of the same hosts to be exported again, then LSF tries to re-export the hosts that already have jobs from the consumer cluster running on them (in this case, the jobs continue running without interruption). If LSF has to kill some jobs from the consumer cluster to remove some hosts from the lease, it selects the hosts according to job run time, so it kills the most recently started jobs.

Selection of Model: 

Consider your own goals and priorities when choosing the best resource-sharing model for your site.

• The job forwarding model can make resources available to jobs from multiple clusters, this flexibility allows maximum throughput when each cluster’s resource usage fluctuates. The resource leasing model can allow one cluster exclusive control of a dedicated resource, this can be more efficient when there is a steady amount of work.
• The lease model is the most transparent to users and supports the same scheduling features as a single cluster.
• The job forwarding model has a single point of administration, while the lease model shares administration between provider and consumer clusters.

In this blog, you could follow  both Lease & Job forward Mode configurations for Spectrum LSF cluster .

[sachin@host1 ~]$ lsid
IBM Spectrum LSF Standard 10.1.0.3
My cluster name is cluster1_p8
My master name is host1
[sachin@host1 ~]$

lsclusters : displays configuration information about LSF clusters

bhosts : Displays hosts and their static and dynamic resources in cluster

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Configuration Files:

/nfs_shared_dir/LSF_HOME/conf/lsf.shared

Begin Cluster
ClusterName  Servers
cluster1_p8     (host1)
cluster2_p9     (host6)
cluster3_x86    (host11)
End Cluster
------------------------------------------------------------
/nfs_shared_dir/LSF_HOME/conf/lsbatch/ppc_cluster1/configdir/lsb.resources

Begin HostExport
PER_HOST     =    host1      # export host list
SLOTS        = 20                   # for each host, export 1 job slots
DISTRIBUTION = ([ cluster2_p9 , 1] [cluster3_x86, 1]) # share distribution for remo
MEM          = 100                 # export 100M mem of each host [optional parameter]
SWP          = 100                 # export 100M swp of each host [optional parameter]
End HostExport
In this example, resources are leased to 2 clusters in an even 1:1 ratio. Each cluster gets 1/2 of the resources. NOTE: This configuration required only for Lease Mode.
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/nfs_shared_dir/LSF_HOME/conf/lsbatch/CI_cluster_ppc/configdir/lsb.queues

Begin Queue
QUEUE_NAME     = send_queue
SNDJOBS_TO     = receive_queue@cluster3_x86
HOSTS          = none
PRIORITY       = 30
NICE           = 20
End Queue

Begin Queue
QUEUE_NAME = leaseq
PRIORITY  = 20
HOSTS = all allremote
End Queue

Begin Queue
QUEUE_NAME   = cluster1_p8
PRIORITY     = 30
INTERACTIVE  = NO
HOSTS        = host1 host2 host3 host4 host5        # hosts on which jobs in this queue can run
DESCRIPTION  = For submission of jobs to P9 machines
End Queue

Begin Queue
QUEUE_NAME   = cluster2_p9
PRIORITY     = 30
INTERACTIVE  = NO
HOSTS        = host6 host7 host8 host9 host10       # hosts on which jobs in this queue can run
DESCRIPTION  = For submission of jobs to P9 machines
End Queue

Begin Queue
QUEUE_NAME   = cluster3_x86
PRIORITY     = 30
INTERACTIVE  = NO
HOSTS        = host11 host12 host13 host14 host15       # hosts on which jobs in this queue can run
DESCRIPTION  = For submission of jobs to P8 machines
End Queue

-------------------------------------------------------------------------------
In case of job forwarding model you need to have following configuration on Remote cluster
/nfs_shared_dir/LSF_HOME/conf/lsbatch/CI_cluster_ppc/configdir/lsb.queues

Begin Queue
QUEUE_NAME      = receive_queue
RCVJOBS_FROM    = send_queue@cluster1_p8
HOSTS           =   host11 host12 host13 host14 host15
PRIORITY        = 55
NICE            = 10
DESCRIPTION     = Multicluster Queue
End Queue

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Check  Job Forwarding Information  and Resource Lease Information by issuing bclusters command :

Submit  LSF job  - forwarding mechanism

Submit  LSF job  - Resource Leasing mechanism

In this article I wanted to illustrate how someone could get started creating their own LSF multi-cluster setup to run their application that needs more computational resource.

Reference:

1. http://www.slac.stanford.edu/comp/unix/package/lsf/LSF8.1_doc/8.0/multicluster/index.htm?multicluster_benefits_mc_lsf.html~main
2. http://www-01.ibm.com/support/docview.wss?uid=isg3T1016097
3. https://www.ibm.com/support/knowledgecenter/en/SSWRJV_10.1.0/lsf_welcome/lsf_kc_mc.html
4. https://tin6150.github.io/psg/3rdParty/lsf4_userGuide/13-multicluster.html