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Advanced Topics

Creating automation scripts

This document briefly details how user/developers can create their own FabSim3 automations.


  • Automation scripts allow user/developers to create their own FabSim3 functionalities. They are usually created and modified within individual plugins.
  • Base automation scripts reside within the FabSim3/fabsim/base subdirectory. These should normally not be modified, but they can serve as examples to create your own functionalities, or as building blocks to create complex functions.
  • Plugin-specific automation scripts reside within the base directory of the respective plugin. The script that will be invoked by default is <plugin_name>.py. For larger plugins, various other Python scripts can surely be imported in this main script.

How to write automation functions

  • All automation functions are written using Python 3.
  • On top of that, they rely on shorthand functionalities as provided by Fabric3. See documentation for more information.
  • Commands to be run on the local client side are called using local().
  • Commands to be run remotely are called using run().


To access a remote resource and scan available modules for a specific name one could write:

def probe(label="undefined"):
  Scans a remote site for the presence of certain software.
  return run("module avail 2>&1 | grep {}".format(label))
This task can then be invoked on the archer supercomputer to search for LAMMPS modules by using
fab archer probe:label=lammps
To run an arbitrary bash script locally one could write:
def blackbox(script="", args=""):
    Black-box script execution.
    for p in env.local_blackbox_path:
        script_file_path = os.path.join(p, script)
        if os.path.exists(os.path.dirname(script_file_path)):
            local("{} {}".format(script_file_path, args))


This function first navigates to the blackbox subdirectory in the local Fabsim3 installation, and subsequently executes the $script in that directory. Also, the freehand use of args give a sequence of parameters etc.

To run LAMMPS on a remote host (part of FabMD) one could write:

def lammps(config,**args):
    Submit a LAMMPS job to the remote queue.
    The job results will be stored with a name pattern as defined in the environment.
    config : config directory to use to define geometry, e.g. config=cylinder
    Keyword arguments:
            cores : number of compute cores to request
            wall_time : wall-time job limit
            memory : memory per node
    job(dict(script='lammps', wall_time='0:15:0', memory='2G'),args)

  • The combination of **args in the declaration with update_environment(args) at the start of the function allows users to specify arbitrary arguments on the command line, and to have those automatically loaded in to the FabSim3 environment.
  • with_config() loads in input files into FabSim3.
  • execute(put_configs,config) copies the configuration information to the right directory at the remote resource. On the last line, LAMMPS is run remotely (shown by script="lammps"), and the values of args are passed on to that function as well, overriding the default wall_time and memory specification on that line if the user has specified those variables explicitly already.

Accessing FabSim commands from Python scripts

To launch FabSim3 commands from Python scripts, we have established a basic Python API. This file can be found here.

We recommend using this API rather than os.system() or subprocess() directly, as it will allow us to fix any emerging bugs in future versions for you.

Create Config Directories

  • Configuration information is stored in subdirectories of either config or FabSim3/plugins/<module_name>/configs (to be implemented).
  • One directory should be created for each individual simulation problem type.
  • Typically, input file names are standardized using default names, to reduce the number of user-specified arguments on the command line (e.g., config.xml for HemeLB).
  • Examples for LAMMPS are provided in the base installation of FabSim3.

FabSim variables

FabSim variables are represented in three different ways:

  • in .yml files as a key-value pair, e.g.:
    number_of_cores: 16
  • within the FabSim Python environment as a member of the env dictionary, e.g.:

    env.number_of_cores = 16

  • within templates as a $ denominated variable, which is to be substituted.

How variables are obtained or introduced:

Variable are obtained from the following sources:

  • Parsed from .yml files such as machines.yml and machines_user.yml, which are loaded on startup.
  • Explicitly written/created in the Python code environment. This should be implemented such that the third method will still override this method.
  • Overridden or introduced using command-line arguments.

How variables are applied

  • Directly, by reading values from env.<variable_name> in the Python code base.
  • Through template substitution, where instances of $<variable_name> are replaced with <variable_value> in the substitution output.
Example of applying a variable
def test_sim(config,**args):
    Submit a my_sim job to the remote queue.

    env.test_var = 300.0 # test variable is set to a default value in the FabSim environment.
    # This will override any defaults set in other parts of FabSim (e.g. machines_user.yml)

    # If a value for test_var is given as a command-line argument,
    # then the default set above will be overridden.

    env.sim_args = "-test-var=%s" % (env.test_var)
    # Optional example how to use your created variable
    # to create some parameter syntax for your job.

    test_sim(config, **args)
    # start a fictitious job, with the variable present in your FabSim environment.

Creating Job Submission Templates

  • Job submission templates are used to convert FabSim environmental information to batch job scripts which can be submitted to remote resource schedulers.
  • Domain-independent templates are stored in FabSim3/fabsim/deploy/templates, while domain-specific templates should be stored in FabSim3/fabsim/deploy/<module_name>/templates.
  • Templates consist of two parts, Header templates which are scheduler-specific, and job execution templates which are code-specific.
  • Normally, one new template needs to be added when adding a new machine definition to FabSim3, regardless of the number of codes used on that machine.
  • Also one new template needs to be added for each new code definition to FabSim3, regardless of the number of machines supported.

Header templates

Header templates are usually created as follows:

  • Take a batch script header example from the user guide of the respective resource.
  • Any existing variable denoted with $name should normally be replaced with $$name (to prevent substitution with FabSim variables).
  • Any hard-coded value should be replaced with a FabSim environment variable name, prefixed with a $ symbol.
  • One then needs to ensure that the respective variables are properly created in FabSim3, e.g. by adding default definitions for them to machines.yml if necessary.

The example below is the batch header template for the SuperMUC supercomputer.

## Copyright (C) University College London, 2007-2012, all rights reserved.
## This file is part of HemeLB and is CONFIDENTIAL. You may not work
## with, install, use, duplicate, modify, redistribute or share this
## file, or any part thereof, other than as allowed by any agreement
## specifically made by you with University College London.
## optional: energy policy tags
# DO NOT USE environment = COPY_ALL

#@ job_name = $job_name_template_sh
#@ job_type = $job_type
#@ output = job$$(jobid).out
#@ error = job$$(jobid).err
#@ class = $job_class
#@ tasks_per_node = $corespernode
#@ island_count = $island_count
#@ node = $nodes
#@ wall_clock_limit = $wall_time
#@ network.MPI = sn_all,shared,us
#@ notification = never
#@ initialdir = .
#@ node_usage = shared
#@ queue

# setup modules
. /etc/profile
. /etc/profile.d/

  • Here, #@ output = job$$(jobid).out will become #@ output = job$(jobid).out after templating, preserving the supercomputer-specific environment variable.
  • However, #@ node = $nodes will for example become #@ node = 16 if the env.nodes value within FabSim3 equals to 16.
  • Note also that the (MPI) execution command should not reside in this template, as this is supplied separately.

Job execution templates

Job execution templates are typically straightforward in their structure, and usually contain just a few preparation commands and a generic MPI job execution formulation.

Here is an example job execution template for the LAMMPS code:

cd $job_results # change directory to the FabSim results dir. Featured in almost all templates.
$run_prefix     # run preparatory commands, as specified within FabSim.

cp -r $job_config_path/* . # Copy over initial conditions to results directory. Featured in almost all templates.
/usr/bin/env > env.log     # Store local supercomputer environment variables. Featured in almost all templates.
$run_command $lammps_exec $lammps_args < $lammps_input > log.lammps # Generically formulated LAMMPS execution command.
The last command will likely depend on how parameters are passed to the target code.

  • $run_command will be substituted by a job execution command such as mpirun or aprun.
  • Other variables contain code/domain-specific information such as input and output destinations, relevant flags or the location of the executable.