Setup Compute

Once a QCFractal server is running, compute can be attached to it by spinning up qcfractal-manager. These qcfractal-manager connect to your FractalServer instance, adds tasks to a distributed workflow manager, and pushes complete tasks back to the qcfractal-server instance. These qcfractal-manager should be run on either the machine that is executing the computations or on the head nodes of supercomputers and local clusters.

Distributed Workflow Engines

QCFractal supports a number of distributed workflow engines to execute computations. Each of these has strengths and weaknesses depending on the workload, task specifications, and resources that the compute will be executed on. In general, we recommend the following:

  • For laptops and single nodes: ProcessPoolExecutor

  • For local clusters: Dask or Parsl

The ProcessPoolExecutor uses built-in Python types and requires no additional libraries while Dask requires dask, dask.distributed, and dask_jobqueue (Dask Distributed Docs, Dask Jobqueue Docs); and Parsl requires parsl (Parsl Docs)

Using the Command Line


The CLI + YAML config file is the current recommended way to start and run Fractal Queue Managers

At the moment only ProcessPoolExecutor qcfractal-manager can be spun up purely from the command line as other distributed workflow managers require additional setup through a YAML config file.

For the full docs for setting up a Manager, please see the Manager documentation pages.

Launching a qcfractal-manager using a ProcessPoolExecutor:

$ fractal-manager executor
[I 190301 10:45:50 managers:118] QueueManager:
[I 190301 10:45:50 managers:119]     Version:         v0.5.0

[I 190301 10:45:50 managers:122]     Name Information:
[I 190301 10:45:50 managers:123]         Cluster:     unknown
[I 190301 10:45:50 managers:124]         Hostname:    qcfractal.local
[I 190301 10:45:50 managers:125]         UUID:        0d2b7704-6ac0-4ef7-b831-00aa6afa8c1c

[I 190301 10:45:50 managers:127]     Queue Adapter:
[I 190301 10:45:50 managers:128]         <ExecutorAdapter client=<ProcessPoolExecutor max_workers=8>>

[I 190301 10:45:50 managers:131]     QCEngine:
[I 190301 10:45:50 managers:132]         Version:    v0.6.1

[I 190301 10:45:50 managers:150]     Connected:
[I 190301 10:45:50 managers:151]         Version:     v0.5.0
[I 190301 10:45:50 managers:152]         Address:     https://localhost:7777/
[I 190301 10:45:50 managers:153]         Name:        QCFractal Server
[I 190301 10:45:50 managers:154]         Queue tag:   None
[I 190301 10:45:50 managers:155]         Username:    None

[I 190301 10:45:50 managers:194] QueueManager successfully started. Starting IOLoop.

The connected qcfractal-server instance can be controlled by:

$ qcfractal-manager

Only basic settings can be started through the CLI and most of the options require a YAML config file to get up and going. You can check all valid YAML options in the Manager documentation pages or you can always check the current schema from the CLI with:

$ qcfractal-manager --schema

The CLI has several options which can examined with:

qcfractal-manager --help

Every option specified in the CLI has an equal option in the YAML config file (except for --help and --schema), but many YAML options are not present in the CLI due to their complex nature. Any option set in both places will defer to the CLI’s setting, allowing you to overwrite some of the common YAML config options on invocation.


The --manager-name argument is useful to change the name of the manager reported back to the Server instance. In addition, the --queue-tag will limit the acquisition of tasks to only the desired Server task tags. These settings can also all be set in the YAML config file.

Using the Python API

qcfractal-managers can also be created using the Python API.


This is for advanced users and special care needs to be taken to ensure that both the manager and the workflow tool need to understand the number of cores and memory available to prevent over-subscription of compute.

from qcfractal.interface import FractalClient
from qcfractal import QueueManager

import dask import distributed

fractal_client = FractalClient("localhost:7777")
workflow_client = distributed.Client("tcp://")

ncores = 4
mem = 2

# Build a manager
manager = QueueManager(fractal_client, workflow_client, cores_per_task=ncores, memory_per_task=mem)

# Important for a calm shutdown
from qcfractal.cli.cli_utils import install_signal_handlers
install_signal_handlers(manager.loop, manager.stop)

# Start or test the loop. Swap with the .test() and .start() method respectively


A qcfractal-manager can be tested using the --test argument and does not require an active qcfractal-manager, this is very useful to check if both the distributed workflow manager is setup correctly and correct computational engines are found.

$ qcfractal-manager --test
[I 190301 10:55:57 managers:118] QueueManager:
[I 190301 10:55:57 managers:119]     Version:         v0.5.0+52.g6eab46f

[I 190301 10:55:57 managers:122]     Name Information:
[I 190301 10:55:57 managers:123]         Cluster:     unknown
[I 190301 10:55:57 managers:124]         Hostname:    Daniels-MacBook-Pro.local
[I 190301 10:55:57 managers:125]         UUID:        0cd257a6-c839-4743-bb33-fa55bebac1e1

[I 190301 10:55:57 managers:127]     Queue Adapter:
[I 190301 10:55:57 managers:128]         <ExecutorAdapter client=<ProcessPoolExecutor max_workers=8>>

[I 190301 10:55:57 managers:131]     QCEngine:
[I 190301 10:55:57 managers:132]         Version:    v0.6.1

[I 190301 10:55:57 managers:158]     QCFractal server information:
[I 190301 10:55:57 managers:159]         Not connected, some actions will not be available
[I 190301 10:55:57 managers:389] Testing requested, generating tasks
[I 190301 10:55:57 managers:425] Found program rdkit, adding to testing queue.
[I 190301 10:55:57 managers:425] Found program torchani, adding to testing queue.
[I 190301 10:55:57 managers:425] Found program psi4, adding to testing queue.
[I 190301 10:55:57 base_adapter:124] Adapter: Task submitted rdkit
[I 190301 10:55:57 base_adapter:124] Adapter: Task submitted torchani
[I 190301 10:55:57 base_adapter:124] Adapter: Task submitted psi4
[I 190301 10:55:57 managers:440] Testing tasks submitting, awaiting results.

[I 190301 10:56:04 managers:444] Testing results acquired.
[I 190301 10:56:04 managers:451] All tasks retrieved successfully.
[I 190301 10:56:04 managers:456]   rdkit - PASSED
[I 190301 10:56:04 managers:456]   torchani - PASSED
[I 190301 10:56:04 managers:456]   psi4 - PASSED
[I 190301 10:56:04 managers:465] All tasks completed successfully!