Slurm Workload Manager - Licenses Guide

# Licenses Guide

## Licenses Overview

Slurm can help with software license management by assigning available licenses to jobs at scheduling time. If the licenses are not available, jobs are kept pending until licenses become available. Licenses in Slurm are essentially shared resources, meaning configured resources that are not tied to a specific host but are associated with the entire cluster.

Licenses in Slurm can be configured in two ways:

- Local Licenses: Local licenses are local to the cluster using the slurm.conf in which they are configured.
- Remote Licenses: Remote licenses are served by the database and are configured using the sacctmgr command. Remote licenses are dynamic in nature as upon running the sacctmgr command, the slurmdbd updates all clusters the licenses are assigned to.

## Local Licenses

Local licenses are defined in the slurm.conf using the Licenses option.

slurm.conf:

    Licenses=fluent:30,ansys:100

Configured licenses can be viewed using the scontrol command.

    $ scontrol show lic
    LicenseName=ansys
        Total=100 Used=0 Free=100 Remote=no
    LicenseName=fluent
        Total=30 Used=0 Free=30 Remote=no

Requesting licenses is done by using the -L, or --licenses, submission option.

    $ sbatch -L ansys:2 script.sh
    Submitted batch job 5212

    $ scontrol show lic
    LicenseName=ansys
        Total=100 Used=2 Free=98 Remote=no
    LicenseName=fluent
        Total=30 Used=0 Free=30 Remote=no

Licenses may also be requested using the --tres-per-task option for job submission. If this approach is used, the license must also be defined in the AccountingStorageTRES option of the slurm.conf.

slurm.conf:

    Licenses=fluent:30
    AccountingStorageTRES=license/fluent

Requesting licenses with the --tres-per-task submission option.

    $ sbatch --tres-per-task=license/fluent:4 script.sh
    Submitted batch job 6482

    $ scontrol show lic
    LicenseName=fluent
        Total=30 Used=4 Free=26 Reserved=0 Remote=no

## Remote Licenses

Remote licenses do not offer any kind of integration with third party license managers by themselves. The use of the "Server" and "ServerType" parameters when creating these licenses is just for informative purposes and does not imply any kind of automatic license management with those servers. It is the responsibility of the system administrator to implement any integration needed with these systems. For example, that would include ensuring that only users requesting remote licenses through Slurm can check out licenses from the license server, or making sure that Slurm's license count stays synchronized with license server's (see Dynamic Licenses).

### Use Case

A site has two license servers, one serves 100 Nastran licenses provided by FlexNet and the other serves 50 Matlab licenses from Reprise License Management. The site has two clusters named "fluid" and "pdf" dedicated to run simulation jobs using both products. The managers want to split the number of Nastran licenses equally between clusters, but assign 70% of the Matlab licenses to cluster "pdf" and the remaining 30% to cluster "fluid".

### Configuring Slurm for the use case

Here we assume that both clusters have been configured correctly in the slurmdbd using the sacctmgr command.

    $ sacctmgr show clusters format=cluster,controlhost
       Cluster     ControlHost
    ---------- ---------------
         fluid     143.11.1.3
           pdf     144.12.3.2

The licenses are added using the sacctmgr command, specifying the total count of licenses and the percentage that should be allocated to each cluster. This can be done either in one step or through a multi-step process.

One step:

    $ sacctmgr add resource name=nastran cluster=fluid,pdf \
      count=100 allowed=50 server=flex_host servertype=flexlm type=license
     Adding Resource(s)
      nastran@flex_host
       Cluster - fluid	50
       Cluster - pdf	50
     Settings
      Name           = nastran
      Server         = flex_host
      Description    = nastran
      ServerType     = flexlm
      Count          = 100
      Type           = License

Multi-step:

    $ sacctmgr add resource name=matlab count=50 server=rlm_host \
      servertype=rlm type=license
     Adding Resource(s)
      matlab@rlm_host
     Settings
      Name           = matlab
      Server         = rlm_host
      Description    = matlab
      ServerType     = rlm
      Count          = 50
      Type           = License

    $ sacctmgr add resource name=matlab server=rlm_host \
      cluster=pdf allowed=70
     Adding Resource(s)
      matlab@rlm_host
       Cluster - pdf	70
     Settings
      Name           = matlab
      Server         = rlm_host
      Count          = 50
      LastConsumed   = 0
      Flags          = (null)
      Type           = License

    $ sacctmgr add resource name=matlab server=rlm_host \
      cluster=fluid allowed=30
     Adding Resource(s)
      matlab@rlm_host
       Cluster - fluid	30
     Settings
      Name           = matlab
      Server         = rlm_host
      Count          = 50
      LastConsumed   = 0
      Flags          = (null)
      Type           = License

The sacctmgr command will now display the grand total of licenses.

    $ sacctmgr show resource
          Name     Server     Type  Count LastConsumed Allocated ServerType                Flags
    ---------- ---------- -------- ------ ------------ --------- ---------- --------------------
       nastran  flex_host  License    100            0       100     flexlm
        matlab   rlm_host  License     50            0       100        rlm
    $ sacctmgr show resource withclusters
          Name     Server     Type  Count LastConsumed Allocated ServerType    Cluster  Allowed                Flags
    ---------- ---------- -------- ------ ------------ --------- ---------- ---------- -------- --------------------
       nastran  flex_host  License    100            0       100     flexlm      fluid       50
       nastran  flex_host  License    100            0       100     flexlm        pdf       50
        matlab   rlm_host  License     50            0       100        rlm      fluid       30
        matlab   rlm_host  License     50            0       100        rlm        pdf       70

The configured licenses are now visible on both clusters using the scontrol command.

    # On cluster "pdf":
    $ scontrol show lic
    LicenseName=matlab@rlm_host
        Total=35 Used=0 Free=35 Reserved=0 Remote=yes
        LastConsumed=0 LastDeficit=0 LastUpdate=2023-02-28T17:01:44
    LicenseName=nastran@flex_host
        Total=50 Used=0 Free=50 Reserved=0 Remote=yes
        LastConsumed=0 LastDeficit=0 LastUpdate=2023-02-28T17:01:44

    # On cluster "fluid":
    $ scontrol show lic
    LicenseName=matlab@rlm_host
        Total=15 Used=0 Free=15 Reserved=0 Remote=yes
        LastConsumed=0 LastDeficit=0 LastUpdate=2023-02-28T17:01:44
    LicenseName=nastran@flex_host
        Total=50 Used=0 Free=50 Reserved=0 Remote=yes
        LastConsumed=0 LastDeficit=0 LastUpdate=2023-02-28T17:01:44

When submitting jobs to remote licenses, the name and server must be used.

    $ sbatch -L nastran@flex_host script.sh
    Submitted batch job 5172

License percentages and counts can be modified as shown below:

    $ sacctmgr modify resource name=matlab server=rlm_host set \
      count=200
     Modified server resource ...
      matlab@rlm_host
      Cluster - fluid	- matlab@rlm_host
      Cluster - pdf	- matlab@rlm_host

    $ sacctmgr modify resource name=matlab server=rlm_host \
      cluster=pdf set allowed=60
     Modified server resource ...
      Cluster - pdf	- matlab@rlm_host

    $ sacctmgr show resource withclusters
          Name     Server     Type  Count LastConsumed Allocated ServerType    Cluster  Allowed                Flags
    ---------- ---------- -------- ------ ------------ --------- ---------- ---------- -------- --------------------
       nastran  flex_host  License    100            0       100     flexlm      fluid       50
       nastran  flex_host  License    100            0       100     flexlm        pdf       50
        matlab   rlm_host  License    200            0        90        rlm      fluid       30
        matlab   rlm_host  License    200            0        90        rlm        pdf       60

Licenses can be deleted either on the cluster or all together as shown:

    $ sacctmgr delete resource where name=matlab server=rlm_host cluster=fluid
     Deleting resource(s)...
     Deleting resource(s)...
      Cluster - fluid	- matlab@rlm_host

    $ sacctmgr delete resource where name=nastran server=flex_host
     Deleting resource(s)...
      nastran@flex_host
      Cluster - fluid	- nastran@flex_host
      Cluster - pdf	- nastran@flex_host

    $ sacctmgr show resource withclusters
          Name     Server     Type  Count LastConsumed Allocated ServerType    Cluster  Allowed                Flags
    ---------- ---------- -------- ------ ------------ --------- ---------- ---------- -------- --------------------
        matlab   rlm_host  License    200            0        60        rlm        pdf       60

Starting with Slurm 23.02, a new Absolute flag is available that indicates the license allowed values for each cluster are to be treated as absolute license counts rather than percentages.

Some brief examples of license management using this flag.

    $ sacctmgr -i add resource name=deluxe cluster=fluid,pdf count=150 allowed=70 \
      server=flex_host servertype=flexlm flags=absolute
     Adding Resource(s)
      deluxe@flex_host
       Cluster - fluid	70
       Cluster - pdf	70
     Settings
      Name           = deluxe
      Server         = flex_host
      Description    = deluxe
      ServerType     = flexlm
      Count          = 150
      Flags          = Absolute
      Type           = Unknown

    $ sacctmgr show resource withclusters
          Name     Server     Type  Count LastConsumed Allocated ServerType    Cluster  Allowed                Flags
    ---------- ---------- -------- ------ ------------ --------- ---------- ---------- -------- --------------------
        deluxe  flex_host  License    150            0       140     flexlm      fluid       70             Absolute
        deluxe  flex_host  License    150            0       140     flexlm        pdf       70             Absolute

    $ sacctmgr -i update resource deluxe set allowed=25 where cluster=fluid
     Modified server resource ...
      Cluster - fluid	- deluxe@flex_host

    $ sacctmgr show resource withclusters
          Name     Server     Type  Count LastConsumed Allocated ServerType    Cluster  Allowed                Flags
    ---------- ---------- -------- ------ ------------ --------- ---------- ---------- -------- --------------------
        deluxe  flex_host  License    150            0        95     flexlm      fluid       25             Absolute
        deluxe  flex_host  License    150            0        95     flexlm        pdf       70             Absolute

This can also be established as the default for all newly created licenses by adding AllResourcesAbsolute=yes to slurmdbd.conf (and restarting SlurmDBD to make the change take effect).

## Dynamic Licenses

Starting with Slurm 23.02, the LastConsumed field for remote licenses is designed to be periodically updated with the active use count from a license server. An example script for FlexLM's lmstat command is provided below — similar scripts can be easily constructed for other license management stacks.

    #!/bin/bash

    set -euxo pipefail

    LMSTAT=/opt/foobar/bin/lmstat
    LICENSE=foobar

    consumed=$(${LMSTAT} | grep "Users of ${LICENSE}"|sed "s/.*Total of \([0-9]\+\) licenses in use)/\1/")

    sacctmgr -i update resource ${LICENSE} set lastconsumed=${consumed}

When the LastConsumed value is changed through sacctmgr an update is automatically pushed to the Slurm controllers. They will use this value to calculate a LastDeficit value — this value indicates how many licenses that have "gone missing" from the cluster's perspective and will need to be set aside temporarily.

E.g., on this cluster 100 "foobar" licenses are available, and we are allocating access to 80 of them on the "blackhole" cluster:

    $ sacctmgr add resource foobar count=100 flags=absolute cluster=blackhole allowed=80
     Adding Resource(s)
      foobar@slurmdb
       Cluster - blackhole	80
     Settings
      Name           = foobar
      Server         = slurmdb
      Description    = foobar
      Count          = 100
      Flags          = Absolute
      Type           = Unknown
    Would you like to commit changes? (You have 30 seconds to decide)
    (N/y): y
    $ scontrol show license
    LicenseName=foobar@slurmdb
        Total=80 Used=0 Free=80 Reserved=0 Remote=yes
        LastConsumed=0 LastDeficit=0 LastUpdate=2023-02-28T16:36:55

Now, our cron job comes in and updates the LastConsumed value to 30, while the cluster has yet to allocate any licenses to jobs:

    $ sacctmgr -i update resource foobar set lastconsumed=30
     Modified server resource ...
      foobar@slurmdb
      Cluster - blackhole	- foobar@slurmdb
    $ scontrol show license
    LicenseName=foobar@slurmdb
        Total=80 Used=0 Free=70 Reserved=0 Remote=yes
        LastConsumed=30 LastDeficit=10 LastUpdate=2023-02-28T16:39:27

Note that the cluster has now calculated a deficit of 10 licenses, and has noticed that it should only schedule up to 70 licenses at the moment. The cluster knows that up to 20 licenses are reserved for other clusters or external use at the moment. However, since LastConsumed was set to 30 this implies an additional 10 licenses have "gone rogue" and their usage cannot be accounted for. Thus the cluster must not assign those to any pending jobs, as it's likely that the job would fail to acquire the desired licenses.

If a further update (likely driven through cron) now reduces the LastConsumed count to 10, the deficit is now considered to have disappeared, and the cluster will make all 80 assigned licenses available again:

    $ sacctmgr -i update resource foobar set lastconsumed=20
     Modified server resource ...
      foobar@slurmdb
      Cluster - blackhole	- foobar@slurmdb
    $ scontrol show license
    LicenseName=foobar@slurmdb
        Total=80 Used=0 Free=80 Reserved=0 Remote=yes
        LastConsumed=20 LastDeficit=0 LastUpdate=2023-02-28T16:44:26