Dask is an open-source parallel computing library for Python that enables the processing of large datasets and complex computations across multiple cores and distributed systems. It provides a flexible and dynamic task scheduling system that allows users to build complex workflows and handle large-scale data processing.

Dask is a compelling alternative to PySpark for distributed computing, particularly for those who work primarily within the Python ecosystem. Dask doesn’t require a Java runtime, and can be imported like any other third-party package. It is much lighter weight because it doesn’t require the heavy infrastructure needed to support Spark computing environments. PySpark typically needs a full Spark cluster setup with distributed resource management and coordination (e.g., YARN or Kubernetes), which involves significant overhead. In contrast, Dask operates within a Python environment and can scale from a single machine to a cluster as needed, without requiring the setup of a full distributed system.

In particular, I was interested in setting up a Dask cluster to leverage my own computing resources rather than rely on cloud resources or deployment software such as colied, which I would almost certainly opt for if creating a cloud-based cluster in a real-world setting.

There were a number of laptops at my disposal in various states of underutilization and disrepair, and figured setting up a compute cluster would be a great way to gain familiarity with Dask, as well as give new life to these otherwise unused machines. In particular, my cluster consists of:

1. Lenovo Slim 7 Pro X (Ubuntu 22.04, 20GB RAM, 1TB SSD, 16 CPU): client/scheduler
2. Sony VAIO (Ubuntu 22.04, 16GB RAM, 512GB SSD, 4 CPU): worker
3. Raspberry Pi 5 (Debian 12.7, 4GB RAM, 128GB SSD, 4 CPU): worker

It is straightforward to extend the cluster to additional workers. The only requirements are 1) the machine be accessible from the client via ssh, and 2) the availability of a Python environment consistent with the other worker nodes in terms of install location and package versions.

I attempted including an additional worker using a Windows client running the same dask conda environment via WSL, but couldn’t get it to work. I’m sure it’s possible, I just didn’t spend the time to configue it properly. I’ll pick this up again down the road and will publish an update.

In order to ensure a consistent environment across workers, I installed Miniforge to the same location on client and worker nodes, and used an environment file save to a GitHub Gist which was referenced at the time of environment creation:

(base) $ conda env create --file=https://gist.githubusercontent.com/jtrive84/f0d23fcf22bb590caefca1e10243aba2/raw/53328d955a4f543581448c6b6033da94058eb245/dask.yaml

The dask environment contains:

name: dask
channels:
- conda-forge
- defaults
dependencies:
- python=3.12
- dask=2024.12.0
- dask-labextension=7.0.0
- numpy=2.2.1
- asyncssh=2.19.0
- pyarrow=18.1.0
- matplotlib=3.9.4
- ipykernel
- watermark
- jupyterlab

The dask-labextension is a JupyterLab extension that provides a user-friendly interface for monitoring Dask clusters from JupyterLab. It provides real-time visualizations of cluster performance and displays worker status, memory usage, and task progress, and offers a high degree of configurability. I highly recommend utilizing the Dask lab extension if managing Dask clusters from JupyterLab.

DaskLab extension

All nodes run within the dask conda environment located at:

~/miniforge3/envs/dask/bin/python

To demonstrate my cluster, I’ll use the Flight Prices dataset available on Kaggle. This is a 31GB dataset containing one-way flight itineraries found on Expedia between 2022-04-16 and 2022-10-05 for airport codes ATL, DFW, DEN, ORD, LAX, CLT, MIA, JFK, EWR, SFO, DTW, BOS, PHL, LGA, IAD and OAK. The file is larger than the client’s available memory, so it couldn’t be analyzed using Pandas which requires the entire dataset to be loaded into RAM. Dask can spill intermediate results to disk for datasets too large to fit into memory, giving us the ability to work with much larger datasets than would otherwise be possible.

To get an idea of what the data looks like, we can read the first 100 records using Pandas:

import numpy as np
import pandas as pd

pd.set_option('display.max_columns', None)
pd.set_option('display.width', None)
np.set_printoptions(suppress=True, precision=5)
pd.options.mode.chained_assignment = None

# Obtained from from https://www.kaggle.com/datasets/dilwong/flightprices
data_path = "~/shared/data/airlines/itineraries.csv"

df = pd.read_csv(data_path, nrows=100)

df.head(7)

# Creating LocalCluster instance.
from dask.distributed import LocalCluster

cluster = LocalCluster(n_workers=2, threads_per_worker=4) 
client = cluster.get_client()

client

2025-01-03 12:16:44,335 - distributed.shuffle._scheduler_plugin - WARNING - Shuffle 8b04cd7a3e831297147d5c00d79f8bb9 initialized by task ('shuffle-transfer-8b04cd7a3e831297147d5c00d79f8bb9', 295) executed on worker tcp://127.0.0.1:33431
2025-01-03 12:18:07,698 - distributed.shuffle._scheduler_plugin - WARNING - Shuffle 8b04cd7a3e831297147d5c00d79f8bb9 deactivated due to stimulus 'task-finished-1735928287.6946151'
2025-01-03 12:19:33,219 - distributed.shuffle._scheduler_plugin - WARNING - Shuffle b7f5ce97ecf82f18ee01140b59d55007 initialized by task ('shuffle-transfer-b7f5ce97ecf82f18ee01140b59d55007', 99) executed on worker tcp://127.0.0.1:33431
2025-01-03 12:20:26,159 - distributed.shuffle._scheduler_plugin - WARNING - Shuffle b7f5ce97ecf82f18ee01140b59d55007 deactivated due to stimulus 'task-finished-1735928426.1586232'
2025-01-03 12:20:35,652 - distributed.shuffle._scheduler_plugin - WARNING - Shuffle 8b04cd7a3e831297147d5c00d79f8bb9 initialized by task ('shuffle-transfer-8b04cd7a3e831297147d5c00d79f8bb9', 405) executed on worker tcp://127.0.0.1:36301
2025-01-03 12:21:36,894 - distributed.shuffle._scheduler_plugin - WARNING - Shuffle 8b04cd7a3e831297147d5c00d79f8bb9 deactivated due to stimulus 'task-finished-1735928496.8918214'

import dask
import dask.dataframe as ddf

data_path = "~/shared/data/airlines/itineraries.csv"

df = ddf.read_csv(
    data_path, 
    usecols=["startingAirport", "destinationAirport", "baseFare", "totalFare"],
    assume_missing=True
)

dfstart = df.groupby("startingAirport").startingAirport.count()

dfstart.compute()

startingAirport
CLT    5494510
MIA    4930213
OAK    3809884
DFW    5674959
ATL    5312028
IAD    3464378
JFK    4425164
DTW    4547052
DEN    4697143
LGA    5919323
BOS    5883876
ORD    5503476
PHL    4726187
EWR    3970797
LAX    8073281
SFO    5706482
Name: startingAirport, dtype: int64

dffare = df.groupby("startingAirport").totalFare.mean()
dffare.compute()

startingAirport
CLT    321.456261
MIA    299.955595
OAK    534.211396
DFW    294.077856
ATL    303.774077
IAD    370.046151
JFK    375.406488
DTW    330.940539
DEN    335.077884
LGA    299.220774
BOS    285.865775
ORD    281.691875
PHL    344.088743
EWR    302.986457
LAX    379.254937
SFO    434.504077
Name: totalFare, dtype: float64

client.shutdown()

from dask.distributed import Client, SSHCluster

# Path to dask environment executable for all nodes. 
remote_python = "~/miniforge3/envs/dask/bin/python"

hosts = ["localhost", "192.168.86.138", "192.168.86.147"]

worker_opts = {"n_workers": 1, "nthreads": 4} #"memory_limit": "8GB"

connect_opts = {
    "known_hosts": None, 
    "username": "jtriz", 
    "password": "xxxxx",
}

cluster = SSHCluster(
    hosts=hosts,
    worker_options=worker_opts,
    connect_options=connect_opts,
    remote_python=remote_python
)

client = Client(cluster)

client

2025-01-03 12:24:23,300 - distributed.deploy.ssh - INFO - 2025-01-03 12:24:23,299 - distributed.scheduler - INFO - State start
2025-01-03 12:24:23,304 - distributed.deploy.ssh - INFO - 2025-01-03 12:24:23,303 - distributed.scheduler - INFO -   Scheduler at: tcp://192.168.86.154:46219
2025-01-03 12:24:24,150 - distributed.deploy.ssh - INFO - 2025-01-03 12:24:24,149 - distributed.nanny - INFO -         Start Nanny at: 'tcp://192.168.86.154:35955'
2025-01-03 12:24:24,161 - distributed.deploy.ssh - INFO - 2025-01-03 12:24:24,160 - distributed.nanny - INFO -         Start Nanny at: 'tcp://192.168.86.154:45391'
2025-01-03 12:24:24,538 - distributed.deploy.ssh - INFO - 2025-01-03 12:24:24,536 - distributed.worker - INFO -       Start worker at: tcp://192.168.86.154:40165
2025-01-03 12:24:24,553 - distributed.deploy.ssh - INFO - 2025-01-03 12:24:24,551 - distributed.worker - INFO -       Start worker at: tcp://192.168.86.154:39183

data_path = "~/shared/data/airlines/itineraries.csv"

df = ddf.read_csv(
    data_path, 
    usecols=["startingAirport", "destinationAirport", "baseFare", "totalFare"],
    assume_missing=True
)

dfstart = df.groupby("startingAirport").startingAirport.count()

dfstart.compute()

startingAirport
CLT    5494510
MIA    4930213
OAK    3809884
DFW    5674959
ATL    5312028
IAD    3464378
JFK    4425164
DTW    4547052
DEN    4697143
LGA    5919323
BOS    5883876
ORD    5503476
PHL    4726187
EWR    3970797
LAX    8073281
SFO    5706482
Name: startingAirport, dtype: int64

dffare = df.groupby("startingAirport").totalFare.mean()
dffare.compute()

startingAirport
CLT    321.456261
MIA    299.955595
OAK    534.211396
DFW    294.077856
ATL    303.774077
IAD    370.046151
JFK    375.406488
DTW    330.940539
DEN    335.077884
LGA    299.220774
BOS    285.865775
ORD    281.691875
PHL    344.088743
EWR    302.986457
LAX    379.254937
SFO    434.504077
Name: totalFare, dtype: float64

client.shutdown()