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<h1>Slurm Power Saving Guide</h1>

<h2 id="contents">Contents<a class="slurm_link" href="#contents"></a></h2>

<ul>
  <li><a href="#overview">Overview</a></li>
  <li><a href="#config">Configuration</a></li>
  <li><a href="#lifecycle">Node Lifecycle</a></li>
  <li><a href="#manual">Manual Power Saving</a></li>
  <li><a href="#resume_suspend">Resume and Suspend Programs</a></li>
  <li><a href="#tolerance">Fault Tolerance</a></li>
  <li><a href="#images">Booting Different Images</a></li>
  <li><a href="#allocations">Use of Allocations</a></li>
  <li><a href="#nodefeatures">Node Features</a></li>
  <li><a href="#hybrid">Hybrid Cluster</a></li>
  <li><a href="#accounting">Cloud Accounting</a></li>
</ul>

<h2 id="overview">Overview<a class="slurm_link" href="#overview"></a></h2>

<p>Slurm provides an integrated mechanism for nodes being suspended (powered
down, placed into power saving mode) and resumed (powered up, restored from
power saving mode) on demand or by request. Nodes that remain <i>IDLE</i> for
<b>SuspendTime</b> will be suspended by <b>SuspendProgram</b> and will be
unavailable for scheduling for <b>SuspendTimeout</b>. Nodes will
automatically be resumed by <b>ResumeProgram</b> to complete work allocated
to them. Nodes that fail to register within <b>ResumeTimeout</b> will become
<i>DOWN</i> and their allocated jobs are requeued. Node power saving can be
manually requested by <code>scontrol update nodename=&lt;nodename&gt;
state=power_&lt;down|up&gt;</code>. The rate of nodes being resumed or
suspended can be controlled by <b>ResumeRate</b> and <b>SuspendRate</b>.</p>

<p>Slurm can be configured to accomplish power saving by managing compute
resources in any cloud provider (e.g. <a href="http://aws.amazon.com/">Amazon
Web Services</a>, <a href="https://cloud.google.com/">Google Cloud
Platform</a>, <a href="https://azure.microsoft.com/">Microsoft Azure</a>) via
their API. These resources can be combined with an existing cluster to
process excess workload (cloud bursting) or it can operate as an independent
and self-contained cluster.</p>

<p>To enable Power Saving operation in Slurm, you must configure the
following:</p>

<ul>
  <li><b>ResumeProgram</b> and <b>SuspendProgram</b> must be defined. Their
  value must be a valid path to a program.</li>

  <li><b>ResumeTimeout</b> and <b>SuspendTimeout</b> must be defined, either
  globally or on at least one partition.</li>

  <li><b>SuspendTime</b> must be defined, either globally or on at least one
  partition, and not be <i>INFINITE</i> or <i>-1</i>.</li>

  <li><b>ResumeRate</b> and <b>SuspendRate</b> must be greater than or equal
  to <i>0</i>.</li>
</ul>

<p>The Slurm control daemon, <i>slurmctld</i>, must be restarted to initially
enable Power Saving operation. Changes in the configuration parameters (e.g.
<b>SuspendTime</b>) will take effect after modifying the <i>slurm.conf</i>
configuration file and executing <code>scontrol reconfigure</code>.</p>

<h2 id="config">Configuration<a class="slurm_link" href="#config"></a></h2>

<p>The following configuration parameters of interest include:</p>

<dl>
  <dt id="DebugFlags"><b>DebugFlags</b><a class="slurm_link" href=
  "#DebugFlags"></a>
  </dt>

  <dd>
    <p>Defines specific subsystems which should provide more detailed event
    logging. Options of interest include:</p>

    <dl>
      <dt id="Power"><b>Power</b><a class="slurm_link" href="#Power"></a>
      </dt>

      <dd>
        <p>Power management plugin and power save (suspend/resume programs)
        details.</p>
      </dd>
    </dl>
  </dd>

  <dt id="ReconfigFlags"><b>ReconfigFlags</b><a class="slurm_link" href=
  "#ReconfigFlags"></a>
  </dt>

  <dd>
    <p>Flags to control various actions that may be taken when an
    <code>scontrol reconfigure</code> command is issued. Options of interest
    include:</p>

    <dl>
      <dt id="KeepPowerSaveSettings"><b>KeepPowerSaveSettings</b><a class=
      "slurm_link" href="#KeepPowerSaveSettings"></a>
      </dt>

      <dd>
        <p>If set, an <code>scontrol reconfigure</code> command will preserve
        the current state of <b>SuspendExcNodes</b>, <b>SuspendExcParts</b>,
        and <b>SuspendExcStates</b>.</p>
      </dd>
    </dl>
  </dd>

  <dt id="ResumeFailProgram"><b>ResumeFailProgram</b><a class="slurm_link" href=
  "#ResumeFailProgram"></a>
  </dt>

  <dd>
    <p>Program to be executed when nodes fail to resume by
    <b>ResumeTimeout</b>. The argument to the program will be the names of
    the failed nodes (using Slurm's hostlist expression format).</p>
  </dd>

  <dt id="ResumeProgram"><b>ResumeProgram</b><a class="slurm_link" href=
  "#ResumeProgram"></a>
  </dt>

  <dd>
    <p>Program to be executed to restore nodes from power saving mode. The
    program executes as <i>SlurmUser</i> (as configured in
    <i>slurm.conf</i>). The argument to the program will be the names of
    nodes to be restored from power savings mode (using Slurm's hostlist
    expression format).</p>

    <p>If the <i>slurmd</i> daemon fails to respond within the configured
    <b>ResumeTimeout</b> value with an updated BootTime, the node will be
    placed in a DOWN state and the job requesting the node will be requeued.
    If the node isn't actually rebooted (e.g. when multiple-slurmd is
    configured) you can start slurmd with the "-b" option to report the node
    boot time as now.</p>

    <p>A job to node mapping is available in JSON format by reading the
    temporary file specified by the <b>SLURM_RESUME_FILE</b> environment
    variable. This file should be used at the beginning of
    <b>ResumeProgram</b> - see the <a href="#tolerance">Fault Tolerance</a>
    section for more details. This program may use the <code>scontrol show
    nodename</code> command to ensure that a node has booted and the
    <i>slurmd</i> daemon started.</p>

    <pre>
SLURM_RESUME_FILE=/proc/1647372/fd/7:
{
  "all_nodes_resume" : "cloud[1-3,7-8]",
  "jobs" : [
    {
      "extra" : "An arbitrary string from --extra",
      "features" : "c1,c2",
      "job_id" : 140814,
      "nodes_alloc" : "cloud[1-4]",
      "nodes_resume" : "cloud[1-3]",
      "oversubscribe" : "OK",
      "partition" : "cloud",
      "reservation" : "resv_1234"
    },
    {
      "extra" : null,
      "features" : "c1,c2",
      "job_id" : 140815,
      "nodes_alloc" : "cloud[1-2]",
      "nodes_resume" : "cloud[1-2]",
      "oversubscribe" : "OK",
      "partition" : "cloud",
      "reservation" : null
    },
    {
      "extra" : null,
      "features" : null
      "job_id" : 140816,
      "nodes_alloc" : "cloud[7-8]",
      "nodes_resume" : "cloud[7-8]",
      "oversubscribe" : "NO",
      "partition" : "cloud_exclusive",
      "reservation" : null
    }
  ]
}
</pre>

    <p>See the <a href="squeue.html#OPT_OverSubscribe">squeue man page</a>
    for possible values for <b>oversubscribe</b>.</p>

    <p><b>NOTE</b>: The <b>SLURM_RESUME_FILE</b> will only exist and be
    usable if Slurm was compiled with the <a href=
    "related_software.html#json">JSON-C</a> serializer library.</p>
  </dd>

  <dt id="ResumeRate"><b>ResumeRate</b><a class="slurm_link" href=
  "#ResumeRate"></a>
  </dt>

  <dd>
    <p>Maximum number of nodes to be removed from power saving mode per
    minute. A value of zero results in no limits being imposed. The default
    value is 300. Use this to prevent rapid increases in power
    consumption.</p>
  </dd>

  <dt id="ResumeTimeout"><b>ResumeTimeout</b><a class="slurm_link" href=
  "#ResumeTimeout"></a>
  </dt>

  <dd>
    <p>Maximum time permitted (in seconds) between when a node resume request
    is issued and when the node is actually available for use. Nodes which
    fail to respond in this time frame will be marked DOWN and the jobs
    scheduled on the node requeued. Nodes which reboot after this time frame
    will be marked DOWN with a reason of "Node unexpectedly rebooted." The
    default value is 60 seconds.</p>
  </dd>

  <dt id="SchedulerParameters"><b>SchedulerParameters</b><a class="slurm_link"
  href="#SchedulerParameters"></a>
  </dt>

  <dd>
    <p>The interpretation of this parameter varies by SchedulerType. Multiple
    options may be comma separated. Options of interest include:</p>

    <dl>
      <dt id="salloc_wait_nodes"><b>salloc_wait_nodes</b><a class="slurm_link"
      href="#salloc_wait_nodes"></a>
      </dt>

      <dd>
        <p>If defined, the salloc command will wait until all allocated nodes
        are ready for use (i.e. booted) before the command returns. By
        default, salloc will return as soon as the resource allocation has
        been made. The salloc command can use the
        <code>--wait-all-nodes</code> option to override this configuration
        parameter.</p>
      </dd>

      <dt id="sbatch_wait_nodes"><b>sbatch_wait_nodes</b><a class="slurm_link"
      href="#sbatch_wait_nodes"></a>
      </dt>

      <dd>
        <p>If defined, the sbatch script will wait until all allocated nodes
        are ready for use (i.e. booted) before the initiation. By default,
        the sbatch script will be initiated as soon as the first node in the
        job allocation is ready. The sbatch command can use the
        <code>--wait-all-nodes</code> option to override this configuration
        parameter.</p>
      </dd>
    </dl>
  </dd>

  <dt id="SlurmctldParameters"><b>SlurmctldParameters</b><a class="slurm_link"
  href="#SlurmctldParameters"></a>
  </dt>

  <dd>
    <p>Comma-separated options identifying slurmctld options. Options of
    interest include:</p>

    <dl>
      <dt id="cloud_dns"><b>cloud_dns</b><a class="slurm_link" href=
      "#cloud_dns"></a>
      </dt>

      <dd>
        <p>By default, Slurm expects that the network addresses for cloud
        nodes won't be known until creation of the node and that Slurm will
        be notified of the node's address upon registration. Since Slurm
        communications rely on the node configuration found in the
        slurm.conf, Slurm will tell the client command, after waiting for all
        nodes to boot, each node's IP address. However, in environments where
        the nodes are in DNS, this step can be avoided by configuring this
        option.</p>
      </dd>

      <dt id="idle_on_node_suspend"><b>idle_on_node_suspend</b><a class=
      "slurm_link" href="#idle_on_node_suspend"></a>
      </dt>

      <dd>
        <p>Mark nodes as idle, regardless of current state, when suspending
        nodes with <b>SuspendProgram</b> so that nodes will be eligible to be
        resumed at a later time.</p>
      </dd>

      <dt id="node_reg_mem_percent"><b>node_reg_mem_percent=#</b><a class=
      "slurm_link" href="#node_reg_mem_percent"></a>
      </dt>

      <dd>
        <p>Percentage of memory a node is allowed to register with without
        being marked as invalid with low memory. Default is 100. For
        State=CLOUD nodes, the default is 90.</p>
      </dd>

      <dt id="power_save_interval"><b>power_save_interval=#</b><a class=
      "slurm_link" href="#power_save_interval"></a>
      </dt>

      <dd>
        <p>How often the power_save thread looks to resume and suspend nodes.
        The power_save thread will do work sooner if there are node state
        changes. Default is 10 seconds.</p>
      </dd>

      <dt id="power_save_min_interval"><b>power_save_min_interval=#</b><a class=
      "slurm_link" href="#power_save_min_interval"></a>
      </dt>

      <dd>
        <p>How often the power_save thread, at a minimum, looks to resume and
        suspend nodes. Default is 0.</p>
      </dd>
    </dl>
  </dd>

  <dt id="SuspendExcNodes"><b>SuspendExcNodes</b><a class="slurm_link" href=
  "#SuspendExcNodes"></a>
  </dt>

  <dd>
    <p>Nodes not subject to suspend/resume logic. This may be used to avoid
    suspending and resuming nodes which are not in the cloud. Alternately the
    suspend/resume programs can treat local nodes differently from nodes
    being provisioned from cloud. Use Slurm's hostlist expression to identify
    nodes with an optional ":" separator and count of nodes to exclude from
    the preceding range. For example <code>nid[10-20]:4</code> will prevent 4
    usable nodes (i.e IDLE and not DOWN, DRAINING or already powered down) in
    the set <code>nid[10-20]</code> from being powered down. Multiple sets of
    nodes can be specified with or without counts in a comma separated list
    (e.g <code>nid[10-20]:4,nid[80-90]:2</code>). By default, no nodes are
    excluded. This value may be updated with scontrol. See
    <b>ReconfigFlags=KeepPowerSaveSettings</b> for setting persistence.</p>
  </dd>

  <dt id="SuspendExcParts"><b>SuspendExcParts</b><a class="slurm_link" href=
  "#SuspendExcParts"></a>
  </dt>

  <dd>
    <p>List of partitions with nodes to never place in power saving mode.
    Multiple partitions may be specified using a comma separator. By default,
    no nodes are excluded. This value may be updated with scontrol. See
    <b>ReconfigFlags=KeepPowerSaveSettings</b> for setting persistence.</p>
  </dd>

  <dt id="SuspendExcStates"><b>SuspendExcStates</b><a class="slurm_link" href=
  "#SuspendExcStates"></a>
  </dt>

  <dd>
    <p>Specifies node states that are not to be powered down automatically.
    Valid states include CLOUD, DOWN, DRAIN, DYNAMIC_FUTURE, DYNAMIC_NORM,
    FAIL, INVALID_REG, MAINTENANCE, NOT_RESPONDING, PERFCTRS, PLANNED, and
    RESERVED. By default, any of these states, if idle for
    <b>SuspendTime</b>, would be powered down. This value may be updated with
    scontrol. See <b>ReconfigFlags=KeepPowerSaveSettings</b> for setting
    persistence.</p>
  </dd>

  <dt id="SuspendProgram"><b>SuspendProgram</b><a class="slurm_link" href=
  "#SuspendProgram"></a>
  </dt>

  <dd>
    <p>Program to be executed to place nodes into power saving mode. The
    program executes as <i>SlurmUser</i> (as configured in
    <i>slurm.conf</i>). The argument to the program will be the names of
    nodes to be placed into power savings mode (using Slurm's hostlist
    expression format).</p>
  </dd>

  <dt id="SuspendRate"><b>SuspendRate</b><a class="slurm_link" href=
  "#SuspendRate"></a>
  </dt>

  <dd>
    <p>Maximum number of nodes to be placed into power saving mode per
    minute. A value of zero results in no limits being imposed. The default
    value is 60. Use this to prevent rapid drops in power consumption.</p>
  </dd>

  <dt id="SuspendTime"><b>SuspendTime</b><a class="slurm_link" href=
  "#SuspendTime"></a>
  </dt>

  <dd>
    <p>Nodes becomes eligible for power saving mode after being idle or down
    for this number of seconds. A negative number disables power saving mode.
    The default value is -1 (disabled).</p>
  </dd>

  <dt id="SuspendTimeout"><b>SuspendTimeout</b><a class="slurm_link" href=
  "#SuspendTimeout"></a>
  </dt>

  <dd>
    <p>Maximum time permitted (in second) between when a node suspend request
    is issued and when the node shutdown is complete. At that time the node
    must ready for a resume request to be issued as needed for new workload.
    The default value is 30 seconds.</p>
  </dd>
</dl>

<h3 id="node_config">Node Configuration<a class="slurm_link" href=
"#node_config"></a></h3>

<p>Node parameters of interest include:</p>

<dl>
  <dt id="Feature"><b>Feature</b><a class="slurm_link" href="#Feature"></a>
  </dt>

  <dd>
    <p>A node feature can be associated with resources acquired from the
    cloud and user jobs can specify their preference for resource use with
    the <code>--constraint</code> option.</p>
  </dd>

  <dt id="NodeName"><b>NodeName</b><a class="slurm_link" href=
  "#NodeName"></a>
  </dt>

  <dd>
    <p>This is the name by which Slurm refers to the node. A name containing
    a numeric suffix is recommended for convenience.</p>
  </dd>

  <dt id="State"><b>State</b><a class="slurm_link" href="#State"></a>
  </dt>

  <dd>
    <p>Nodes which are to be added on demand should have a state of
    <i>CLOUD</i>.</p>
  </dd>

  <dt id="Weight"><b>Weight</b><a class="slurm_link" href="#Weight"></a>
  </dt>

  <dd>
    <p>Each node can be configured with a weight indicating the desirability
    of using that resource. Nodes with lower weights are used before those
    with higher weights. The default value is 1.</p>
  </dd>
</dl>

<h3 id="part_config">Partition Configuration<a class="slurm_link" href=
"#part_config"></a></h3>

<p>Partition parameters of interest include:</p>

<dl>
  <dt id="PowerDownOnIdle"><b>PowerDownOnIdle</b><a class="slurm_link" href=
  "#PowerDownOnIdle"></a>
  </dt>

  <dd>
    <p>If set to <i>YES</i> and power saving is enabled for the partition,
    then nodes allocated from this partition will be requested to power down
    after being allocated at least one job. These nodes will not power down
    until they transition from COMPLETING to IDLE. If set to <i>NO</i> then
    power saving will operate as configured for the partition. The default
    value is <i>NO</i>.</p>

    <p>The following will cause a transition from <i>COMPLETING</i> to
    <i>IDLE</i>:</p>

    <ul>
      <li>Completing all running jobs without additional jobs being
      allocated.</li>

      <li><i>ExclusiveUser=YES</i> and after all running jobs complete but
      before another user's job is allocated.</li>

      <li><i>OverSubscribe=EXCLUSIVE</i> and after the running job completes
      but before another job is allocated.</li>
    </ul>

    <p><b>NOTE</b>: Nodes are still subject to powering down when being IDLE
    for <b>SuspendTime</b> when PowerDownOnIdle is set to NO.</p>
  </dd>

  <dt id="ResumeTimeout_1"><b>ResumeTimeout</b><a class="slurm_link" href=
  "#ResumeTimeout_1"></a>
  </dt>

  <dd>
    <p>Maximum time permitted (in seconds) between when a node resume request
    is issued and when the node is actually available for use. Nodes which
    fail to respond in this time frame will be marked DOWN and the jobs
    scheduled on the node requeued. Nodes which reboot after this time frame
    will be marked DOWN with a reason of "Node unexpectedly rebooted." The
    default value is 60 seconds.</p>

    <p>For nodes that are in multiple partitions with this option set, the
    highest time will take effect. If not set on any partition, the node will
    use the <b>ResumeTimeout</b> value set for the entire cluster.</p>
  </dd>

  <dt id="SuspendTime_1"><b>SuspendTime</b><a class="slurm_link" href=
  "#SuspendTime_1"></a>
  </dt>

  <dd>
    <p>Nodes which remain idle or down for this number of seconds will be
    placed into power saving mode by <b>SuspendProgram</b>.</p>

    <p>For nodes that are in multiple partitions with this option set, the
    highest time will take effect. If not set on any partition, the node will
    use the <b>SuspendTime</b> value set for the entire cluster. Setting
    <b>SuspendTime</b> to <i>INFINITE</i> will disable suspending of nodes in
    this partition.</p>
  </dd>

  <dt id="SuspendTimeout_1"><b>SuspendTimeout</b><a class="slurm_link" href=
  "#SuspendTimeout_1"></a>
  </dt>

  <dd>
    <p>Maximum time permitted (in second) between when a node suspend request
    is issued and when the node shutdown is complete. At that time the node
    must ready for a resume request to be issued as needed for new workload.
    The default value is 30 seconds.</p>

    <p>For nodes that are in multiple partitions with this option set, the
    highest time will take effect. If not set on any partition, the node will
    use the <b>SuspendTimeout</b> value set for the entire cluster.</p>
  </dd>
</dl>

<h2 id="lifecycle">Node Lifecycle</b><a class="slurm_link" href=
"#lifecycle"></a></h2>

<p>When Slurm is configured for Power Saving operation, nodes have an
expanded set of states associated with them. States associated with Power
Saving are generally labeled with a symbol when viewing node details with
<code>sinfo</code>.</p>

<div class="figure">
  <img src="node_lifecycle.png" alt="Figure 1. Node Lifecycle" width=
  "1000" /><br />
  Figure 1. Node Lifecycle
</div>

<p>Node states of interest:</p>

<div>
  <table cellpadding="8">
    <tbody>
      <tr>
        <td><u><b>STATE</b></u>
        </td>
        <td style="text-align:center"><b><u>Power Saving Symbol</u></b>
        </td>
        <td><u><b>Description</b></u>
        </td>
      </tr>

      <tr>
        <td>POWER_DOWN</td>
        <td style="text-align:center">!</td>
        <td>Power down request. When the node is no longer running job(s),
        run the <b>SuspendProgram</b>.</td>
      </tr>

      <tr>
        <td>POWER_UP</td>
        <td style="text-align:center">&nbsp;</td>
        <td>Power up request. When possible, run the
        <b>ResumeProgram</b>.</td>
      </tr>

      <tr>
        <td>POWERED_DOWN</td>
        <td style="text-align:center">~</td>
        <td>The node is powered down or in power saving mode.</td>
      </tr>

      <tr>
        <td>POWERING_DOWN</td>
        <td style="text-align:center">%</td>
        <td>The node is in the process of powering down, or being put into
        power saving mode, and is not capable of running any jobs for
        <b>SuspendTimeout</b>.</td>
      </tr>

      <tr>
        <td>POWERING_UP</td>
        <td style="text-align:center">#</td>
        <td>The node is in the process of powering up, or being restored from
        power saving mode.</td>
      </tr>
    </tbody>
  </table>
</div>

<h2 id="manual">Manual Power Saving<a class="slurm_link" href=
"#manual"></a></h2>

<p>A node can be manually powered up and down by setting the state of the
node to the following states using <code>scontrol</code>:</p>

<pre>
scontrol update nodename=&lt;nodename&gt; state=power_&lt;down|down_asap|down_force|up&gt;
</pre>

<p><code>scontrol update</code> command actions/states of interest:</p>

<dl>
  <dt id="POWER_DOWN"><b>POWER_DOWN</b><a class="slurm_link" href=
  "#POWER_DOWN"></a>
  </dt>

  <dd>Will use the configured <b>SuspendProgram</b> program to explicitly
  place a node in power saving mode. If a node is already in the process of
  being powered down, the command will only change the state of the node but
  won't have any effect until the configured <b>SuspendTimeout</b> is
  reached.</dd>

  <dt id="POWER_DOWN_ASAP"><b>POWER_DOWN_ASAP</b><a class="slurm_link" href=
  "#POWER_DOWN_ASAP"></a>
  </dt>

  <dd>Will drain the node and mark it for power down. Currently running jobs
  will complete first and no additional jobs will be allocated to the
  node.</dd>

  <dt id="POWER_DOWN_FORCE"><b>POWER_DOWN_FORCE</b><a class="slurm_link" href=
  "#POWER_DOWN_FORCE"></a>
  </dt>

  <dd>Will cancel all jobs on the node, power it down, and reset its state to
  <i>IDLE</i>.</dd>

  <dt id="POWER_UP"><b>POWER_UP</b><a class="slurm_link" href=
  "#POWER_UP"></a>
  </dt>

  <dd>Will use the configured <b>ResumeProgram</b> program to explicitly move
  a node out of power saving mode. If a node is already in the process of
  being powered up, the command will only change the state of the node but
  won't have any effect until the configured <b>ResumeTimeout</b> is
  reached.</dd>

  <dt id="RESUME"><b>RESUME</b><a class="slurm_link" href="#RESUME"></a>
  </dt>

  <dd>Not an actual node state, but will change a node state from DRAIN,
  DRAINING, DOWN or REBOOT to IDLE and NoResp. slurmctld will then attempt to
  contact slurmd to request that the node register itself. Once registered,
  the node state will then remove the NoResp flag and will resume normal
  operations. It will also clear the POWERING_DOWN state of a node and make
  it eligible to be allocated.</dd>
</dl>

<h2 id="resume_suspend">Resume and Suspend Programs<a class="slurm_link"
href="#resume_suspend"></a></h2>

<p>The <b>ResumeProgram</b> and <b>SuspendProgram</b> execute as
<i>SlurmUser</i> on the node where the <i>slurmctld</i> daemon runs (primary
and backup server nodes). Use of <i>sudo</i> may be required for
<i>SlurmUser</i> to power down and restart nodes. If you need to convert
Slurm's hostlist expression into individual node names, the <code>scontrol
show hostnames</code> command may prove useful. The commands used to boot or
shut down nodes will depend upon your cluster management tools.</p>

<p>The <b>ResumeProgram</b> and <b>SuspendProgram</b> are not subject to any
time limits but must have <a href="#tolerance">Fault Tolerance</a>. They
should perform the required action, ideally verify the action (e.g. node boot
and start the <i>slurmd</i> daemon, thus the node is no longer non-responsive
to <i>slurmctld</i>) and terminate. Long running programs will be logged by
<i>slurmctld</i>, but not aborted.</p>

<p>Example <b>ResumeProgram</b>:</p>

<pre>
#!/bin/bash
# Example ResumeProgram
hosts=$(scontrol show hostnames "$1")
logfile=/var/log/power_save.log
echo "$(date) Resume invoked $0 $*" &gt;&gt;$logfile
for host in $hosts
do
        sudo node_startup "$host"
done
exit 0
</pre>

<p>Example <b>SuspendProgram</b>:</p>

<pre>
#!/bin/bash
# Example SuspendProgram
hosts=$(scontrol show hostnames "$1")
logfile=/var/log/power_save.log
echo "$(date) Suspend invoked $0 $*" &gt;&gt;$logfile
for host in $hosts
do
        sudo node_shutdown "$host"
done
exit 0
</pre>

<p><b>NOTE</b>: the stderr and stdout of the suspend and resume programs are
not logged. If logging is desired, then it should be added to the
scripts.</p>

<h2 id="tolerance">Fault Tolerance<a class="slurm_link" href=
"#tolerance"></a></h2>

<p>If the <i>slurmctld</i> daemon is terminated gracefully, it will wait up
to ten seconds (or the maximum of <b>SuspendTimeout</b> or
<b>ResumeTimeout</b> if less than ten seconds) for any spawned
<b>SuspendProgram</b> or <b>ResumeProgram</b> to terminate before the daemon
terminates. If the spawned program does not terminate within that time
period, the event will be logged and <i>slurmctld</i> will exit in order to
permit another <i>slurmctld</i> daemon to be initiated. Any spawned
<b>SuspendProgram</b> or <b>ResumeProgram</b> will continue to run.</p>

<p>When the slurmctld daemon shuts down, any <b>SLURM_RESUME_FILE</b>
temporary files are no longer available, even once slurmctld restarts.
Therefore, <b>ResumeProgram</b> should use <b>SLURM_RESUME_FILE</b> within
ten seconds of starting to guarantee that it still exists.</p>

<h2 id="images">Booting Different Images<a class="slurm_link" href=
"#images"></a></h2>

<p>If you want <b>ResumeProgram</b> to boot various images according to job
specifications, it will need to be a fairly sophisticated program and perform
the following actions:</p>

<ol>
  <li>Determine which jobs are associated with the nodes to be booted.
  <b>SLURM_RESUME_FILE</b> will help with this step.</li>

  <li>Determine which image is required for each job. Images can be mapped
  with <a href="#nodefeatures">NodeFeaturesPlugins</a>.
  </li>

  <li>Boot the appropriate image for each node.</li>
</ol>

<h2 id="allocations">Use of Allocations<a class="slurm_link" href=
"#allocations"></a></h2>

<p>A resource allocation request will be granted as soon as resources are
selected for use, possibly before the nodes are all available for use. The
launching of job steps will be delayed until the required nodes have been
restored to service (it prints a warning about waiting for nodes to become
available and periodically retries until they are available).</p>

<p>In the case of an <i>sbatch</i> command, the batch program will start when
node zero of the allocation is ready for use and pre-processing can be
performed as needed before using <i>srun</i> to launch job steps. The
<i>sbatch</i> <code>--wait-all-nodes=&lt;value&gt;</code> option can be used
to override this behavior on a per-job basis and a system-wide default can be
set with the <i>SchedulerParameters=sbatch_wait_nodes</i> option.</p>

<p>In the case of the <i>salloc</i> command, once the allocation is made a
new shell will be created on the login node. The <i>salloc</i>
<code>--wait-all-nodes=&lt;value&gt;</code> option can be used to override
this behavior on a per-job basis and a system-wide default can be set with
the <i>SchedulerParameters=salloc_wait_nodes</i> option.</p>

<h2 id="nodefeatures">Node Features<a class="slurm_link" href=
"#nodefeatures"></a></h2>

<p>Features defined by <a href=
"slurm.conf.html#OPT_NodeFeaturesPlugins">NodeFeaturesPlugins</a>, and
associated to cloud nodes in the <b>slurm.conf</b>, will be available but not
active when the node is powered down. If a job requests available nut not
active features, the controller will allocate nodes that are powered down and
have the features as available. At allocation, the features will be made
active. A cloud node will remain with the active features until the node is
powered down (i.e. the node can't be rebooted to get other features until the
node is powered down). When the node is powered down, the those features
become available but not active. Any feature not defined by
NodeFeaturesPlugins are always active.</p>

<p>Example:</p>

<pre>
slurm.conf:
NodeFeaturesPlugins=node_features/helpers

NodeName=cloud[1-5] ... State=CLOUD Feature=f1,f2,l1
NodeName=cloud[6-10] ... State=CLOUD Feature=f3,f4,l2

helpers.conf:
NodeName=cloud[1-5] Feature=f1,f2 Helper=/bin/true
NodeName=cloud[6-10] Feature=f3,f4 Helper=/bin/true
</pre>

<p>Features f1, f2, f3, and f4 are changeable features and are defined on the
node lines in the slurm.conf because <i>CLOUD</i> nodes do not register
before being allocated. By setting the <i>Helper</i> script to /bin/true, the
slurmd's will not report any active features to the controller and the
controller will manage all the active features. If the <i>Helper</i> is set
to a script that reports the active features, the controller will validate
that the reported active features are a super set of the node's active
changeable features in the controller. Features l1 and l2 will always be
active and can be used as selectable labels.</p>

<h2 id="hybrid">Hybrid Cluster<a class="slurm_link" href="#hybrid"></a></h2>

<p>Cloud nodes to be acquired on demand can be placed into their own Slurm
partition. This mode of operation can be used to use these nodes only if so
requested by the user. Note that jobs can be submitted to multiple partitions
and will use resources from whichever partition permits faster initiation. A
sample configuration in which nodes are added from the cloud when the
workload exceeds available resources. Users can explicitly request local
resources or resources from the cloud by using the <code>--constraint</code>
option.</p>

<p>Example:</p>

<pre>
# Excerpt of slurm.conf
SelectType=select/cons_tres
SelectTypeParameters=CR_CORE_Memory

SuspendProgram=/usr/sbin/slurm_suspend
ResumeProgram=/usr/sbin/slurm_resume
SuspendTime=600
SuspendExcNodes=tux[0-127]
TreeWidth=128

NodeName=DEFAULT    Sockets=1 CoresPerSocket=4 ThreadsPerCore=2
NodeName=tux[0-127] Weight=1 Feature=local State=UNKNOWN
NodeName=ec[0-127]  Weight=8 Feature=cloud State=CLOUD
PartitionName=debug MaxTime=1:00:00 Nodes=tux[0-32] Default=YES
PartitionName=batch MaxTime=8:00:00 Nodes=tux[0-127],ec[0-127]
</pre>

<p>When <b>SuspendTime</b> is set globally, Slurm attempts to suspend all
nodes unless excluded by <b>SuspendExcNodes</b> or <b>SuspendExcParts</b>. It
can be tricky to have to remember to add on-premise nodes to the excluded
options. By setting the global <b>SuspendTime</b> to <i>INFINITE</i> and
configuring <b>SuspendTime</b> on cloud specific partitions, you can avoid
having to exclude nodes.</p>

<p>Example:</p>

<pre>
# Excerpt of slurm.conf
SelectType=select/cons_tres
SelectTypeParameters=CR_CORE_Memory

SuspendProgram=/usr/sbin/slurm_suspend
ResumeProgram=/usr/sbin/slurm_resume
TreeWidth=128

NodeName=DEFAULT    Sockets=1 CoresPerSocket=4 ThreadsPerCore=2
NodeName=tux[0-127] Weight=1 Feature=local State=UNKNOWN
NodeName=ec[0-127]  Weight=8 Feature=cloud State=CLOUD
PartitionName=debug MaxTime=1:00:00 Nodes=tux[0-32] Default=YES
PartitionName=batch MaxTime=8:00:00 Nodes=tux[0-127],ec[0-127]
PartitionName=cloud Nodes=ec[0-127] SuspendTime=600
</pre>

<p>Here we have configured a partition with only cloud nodes and defined
<b>SuspendTime</b> on that partition. Doing so will allow us to control when
those nodes power down without affecting our on-premise nodes, therefore
<b>SuspendExcNodes</b> or <b>SuspendExcParts</b> are not needed in this
setup.</p>

<h2 id="accounting">Cloud Accounting<a class="slurm_link" href=
"#accounting"></a></h2>

<p>Information about cloud instances can be stored in the database. This can
be done by configuring instance id/type upon slurmd startup or with
<i>scontrol update</i>. The node's "extra" field will also be stored in the
database.</p>

<p>Configuring cloud information on slurmd startup:</p>

<pre>
$ slurmd --instance-id=12345 --instance-type=m7g.medium --extra="arbitrary string" . . .
</pre>

<p>Configuring cloud information with scontrol update:</p>

<pre>
$ scontrol update nodename=n1 instanceid=12345 instancetype=m7g.medium extra="arbitrary string"
</pre>

<p>This data can then be seen on the controller with <i>scontrol show
node</i>. Past and current data can be seen in the database with <i>sacctmgr
show instance</i>, as well as through slurmrestd with the <i>/instance</i>
and <i>/instances</i> endpoints.</p>

<p>Showing cloud information on the controller with scontrol:</p>

<pre>
$ scontrol show nodes n1 | grep "NodeName\|Extra\|Instance"
NodeName=n1 Arch=x86_64 CoresPerSocket=4
   Extra=arbitrary string
   InstanceId=12345 InstanceType=m7g.medium
</pre>

<p>Showing cloud information from the database with sacctmgr:</p>

<pre>
$ sacctmgr show instance format=nodename,instanceid,instancetype,extra
NodeName                  InstanceId         InstanceType                Extra
--------------- -------------------- -------------------- --------------------
n1                             12345           m7g.medium     arbitrary string
</pre>

<p>Showing cloud information from the database with slurmrestd:</p>

<pre>
$ curl -k -s \
        --request GET \
        -H X-SLURM-USER-NAME:$(whoami) \
        -H X-SLURM-USER-TOKEN:$SLURM_JWT \
        -H "Content-Type: application/json" \
        --url localhost:8080/slurmdb/v0.0.40/instances \
        | jq ".instances"

[
  {
    "cluster": "c1",
    "extra": "arbitrary string",
    "instance_id": "12345",
    "instance_type": "m7g.medium",
    "node_name": "n1",
    "time": {
      "time_end": 0,
      "time_start": 1687213177
    }
  }
]
</pre>

<p style="text-align:center;">Last modified 02 February 2024</p>
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