# Moab Cluster Suite Integration Guide

## Overview

Moab Cluster Suite configuration is quite complicated and is beyond the scope of any documents we could supply with Slurm. The best resource for Moab configuration information is the online documents at Cluster Resources Inc.: http://www.clusterresources.com/products/mwm/docs/slurmintegration.shtml.

Moab use. Slurm commands and a wiki interface to communicate. See the Wiki Interface Specification and Wiki Socket Protocol Description for more information.

Somewhat more current information abou. Slurm's implementation of the wiki interface was developed by Michal Novotny (Masaryk University, Czech Republic) and can be found here.

## Configuration

First, download the Moab scheduler kit from their web site http://www.clusterresources.com/pages/products/moab-cluster-suite.php.
Note: Use Moab version 5.0.0 or higher and Slurm version 1.1.28 or higher.

### Slurm configuration

#### slurm.conf

Set the slurm.conf scheduler parameters as follows:

    SchedulerType=sched/wiki2
    SchedulerPort=7321

Running multiple jobs per mode can be accomplished in two different ways. The SelectType=select/cons_res parameter can be used to let Slurm allocate the individual processors, memory, and other consumable resources. Alternately, SelectType=select/linear or SelectType=select/bluegene can be used with the OverSubscribe=yes or OverSubscribe=force parameter in partition configuration specifications.

The default value of SchedulerPort is 7321.

Slurm has some internal scheduling capabilities which are not compatible with Moab.

1. Do not configure Slurm to use the "priority/multifactor" plugin as it would set job priorities which conflict with those set by Moab.
2. Do not use Slurm's reservation mechanism, but use that offered by Moab.
3. Do not use Slurm's resource limits as those may conflict with those managed by Moab.

#### Slurm commands

Note that the srun --immediate option is not compatible with Moab. All jobs must wait for Moab to schedule them rather than being scheduled immediately by Slurm.

#### wiki.conf

Slurm's wiki configuration is stored in a file specific to the wiki-plugin named wiki.conf. This file should be protected from reading by users. It only needs to be readable by SlurmUser (as configured in slurm.conf) and only needs to exist on computers where the slurmctld daemon executes. More information about wiki.conf is available in a man page distributed with Slurm.

The currently supported wiki.conf keywords include:

AuthKey is a DES based encryption key used to sign communications between Slurm and Maui or Moab. This use of this key is essential to insure that a user not build his own program to cancel other user's jobs in Slurm. This should be no more than 32-bit unsigned integer and match the encryption key in Maui (--with-key on the configure line) or Moab (KEY parameter in the moab-private.cfg file). Note tha. Slurm's wiki plugin does not include a mechanism to submit new jobs, so even without this key, nobody can run jobs as another user.

EPort is an event notification port in Moab. When a job is submitted to or terminates in Slurm, Moab is sent a message on this port to begin an attempt to schedule the computer. This numeric value should match EPORT configured in the moab.cnf file.

EHost is the event notification host for Moab. This identifies the computer on which the Moab daemons executes which should be notified of events. By default EHost will be identical in value to the ControlAddr configured in slurm.conf.

EHostBackup is the event notification backup host for Moab. Names the computer on which the backup Moab server executes. It is used in establishing a communications path for event notification. By default EHostBackup will be identical in value to the BackupAddr configured in slurm.conf.

ExcludePartitions is used to identify partitions whose jobs are to be scheduled directly b. Slurm rather than Moab. This only affects jobs which are submitted using Slurm commands (i.e. srun, salloc or sbatch, NOT msub from Moab). These jobs will be scheduled on a First-Come-First-Served basis. This may provide faster response times than Moab scheduling. Moab will account for and report the jobs, but their initiation will be outside of Moab's control. Note that Moab controls for resource reservation, fair share scheduling, etc. will not apply to the initiation of these jobs. If more than one partition is to be scheduled directly by Slurm, use a comma separator between their names.

HidePartitionJobs identifies partitions whose jobs are not to be reported to Moab. These jobs will not be accounted for or otherwise visible to Moab. Any partitions listed here must also be listed in ExcludePartitions. If more than one partition is to have its jobs hidden, use a comma separator between their names.

HostFormat controls the format of job task lists built by Slurm and reported to Moab. The default value is "0", for which each host name is listed individually, once per processor (e.g. "tux0:tux0:tux1:tux1:..."). A value of "1" use. Slurm hostlist expressions with processor counts (e.g. "tux[0-16]*2"). This is currently experimental.

JobAggregationTime is used to avoid notifying Moab of large numbers of events occurring about the same time. If an event occurs within this number of seconds since Moab was last notified of an event, another notification is not sent. This should be an integer number of seconds. The default value is 10 seconds. The value should match JOBAGGREGATIONTIME configured in the moab.cnf file.

JobPriority controls the scheduling of newly arriving jobs in Slurm. Possible values are "hold" and "run" with "hold" being the default. When JobPriority=hold, Slurm places all newly arriving jobs in a HELD state (priority = 0) and lets Moab decide when and where to run the jobs. When JobPriority=run, Slurm controls when and where to run jobs. Note: The "run" option implementation has yet to be completed. Once the "run" option is available, Moab will be able to modify the priorities of pending jobs to re-order the job queue.

#### Sample wiki.conf file

    # wiki.conf
    . Slurm's wiki plugin configuration file
    #
    # Matches KEY in moab-private.cfg
    AuthKey=123456789
    #
    # Slurm to directly schedule "debug" partition
    # and hide the jobs from Moab
    ExcludePartitions=debug
    HidePartitionJobs=debug
    #
    # Have Moab control job scheduling
    JobPriority=hold
    #
    # Moab event notification port, matches EPORT in moab.cfg
    EPort=15017
    # Moab event notification host, where the Moab daemon runs
    #EHost=tux0
    #
    # Moab event notification throttle,
    # matches JOBAGGREGATIONTIME in moab.cfg (seconds)
    JobAggregationTime=15

### Moab Configuration

Moab has support for Slurm's WIKI interface by default. Specify this interface in the moab.cfg file as follows:

    SCHEDCFG[base]       MODE=NORMAL
    RMCFG[slurm]         TYPE=WIKI:Slurm AUTHTYPE=CHECKSUM

In moab-private.cfg specify the private key as follows:

    CLIENTCFG[RM:slurm] KEY=123456789

Insure that this file is protected from viewing by users.

### Job Submission

Jobs can either be submitted to Moab or directly to Slurm. Moab's msub command has a --slurm option that can be placed at the end of the command line and those options will be passed to Slurm. This can be used to invoke Slurm options which are not directly supported by Moab (e.g. system images to boot, task distribution specification across sockets, cores, and hyperthreads, etc.). For example:

    msub my.script -l walltime=600,nodes=2 \
         --slurm --linux-image=/bgl/linux_image2

### User Environment

When a user submits a job to Moab, that job could potentially execute on a variety of computers, so it is typically necessary that the user's environment on the execution host be loaded. Moab relies upon Slurm to perform this action, using the --get-user-env option for the salloc, sbatch and srun commands. The Slurm command then executes as user root a command of this sort as user root:

    /bin/su - <user> -c \
            "/bin/echo BEGIN; /bin/env; /bin/echo FINI"

For typical batch jobs, the job transfer from Moab to Slurm is performed using sbatch and occurs instantaneously. The environment is loaded by a Slurm daemon (slurmd) when the batch job begins execution. For interactive jobs (msub -I ...), the job transfer from Moab to Slurm cannot be completed until the environment variables are loaded, during which time the Moab daemon is completely non-responsive. To insure that Moab remains operational, Slurm will abort the above command within a configurable period of time and look for a cache file with the user's environment and use that if found. Otherwise an error is reported to Moab. The time permitted for loading the current environment before searching for a cache file is configurable using the GetEnvTimeout parameter in Slurm's configuration file, slurm.conf. A value of zero results in immediately using the cache file. The default value is 2 seconds.

We have provided a simple program that can be used to build cache files for users. The program can be found in the Slurm distribution at contribs/env_cache_builder.c. This program can support a longer timeout than Moab, but will report errors for users for whom the environment file cannot be automatically build (typically due to the user's "dot" files spawning another shell so the desired command never execution). For such user, you can manually build a cache file. You may want to execute this program periodically to capture information for new users or changes in existing users' environment. A sample execution is shown below. Run this on the same host as the Moab daemon and execute it as user root.

    bash-3.00# make -f /dev/null env_cache_builder
    cc     env_cache_builder.c   -o env_cache_builder
    bash-3.00# ./env_cache_builder
    Building user environment cache files for Moab/Slurm.
    This will take a while.

    Processed 100 users...
    ***ERROR: Failed to get current user environment variables for alice
    ***ERROR: Failed to get current user environment variables for brian
    Processed 200 users...
    Processed 300 users...
    ***ERROR: Failed to get current user environment variables for christine
    ***ERROR: Failed to get current user environment variables for david

    Some user environments could not be loaded.
    Manually run 'env' for those 4 users.
    Write the output to a file with the same name as the user in the
      /usr/local/tmp/slurm/atlas/env_cache directory

Last modified 31 March 2016