Tags: Containerization, Intermediate


This is an experimental feature, which is subject to change the API in the future.

ImageSpec is a way to specify how to build a container image without a Dockerfile. The ImageSpec by default will be converted to an Envd config, and the Envd builder will build the image for you. However, you can also register your own builder to build the image using other tools.

For every flytekit.PythonFunctionTask task or a task decorated with the @task decorator, you can specify rules for binding container images. By default, flytekit binds a single container image, i.e., the default Docker image, to all tasks. To modify this behavior, use the container_image parameter available in the flytekit.task() decorator, and pass an ImageSpec.

Before building the image, Flytekit checks the container registry first to see if the image already exists. By doing so, it avoids having to rebuild the image over and over again. If the image does not exist, flytekit will build the image before registering the workflow, and replace the image name in the task template with the newly built image name.

import typing

import pandas as pd
from flytekit import ImageSpec, Resources, task, workflow


  • Install flytekitplugins-envd to build the ImageSpec.

  • To build the image on remote machine, check this doc.

  • When using a registry in ImageSpec, docker login is required to push the image

You can specify python packages, apt packages, and environment variables in the ImageSpec. These specified packages will be added on top of the default image, which can be found in the Flytekit Dockerfile. More specifically, flytekit invokes DefaultImages.default_image() function. This function determines and returns the default image based on the Python version and flytekit version. For example, if you are using python 3.8 and flytekit 0.16.0, the default image assigned will be If desired, you can also override the default image by providing a custom base_image parameter when using the ImageSpec.

pandas_image_spec = ImageSpec(
    packages=["pandas", "numpy"],
    env={"Debug": "True"},

sklearn_image_spec = ImageSpec(


Replace with a container registry you’ve access to publish to. To upload the image to the local registry in the demo cluster, indicate the registry as localhost:30000.

is_container is used to determine whether the task is utilizing the image constructed from the ImageSpec. If the task is indeed using the image built from the ImageSpec, it will then import Tensorflow. This approach helps minimize module loading time and prevents unnecessary dependency installation within a single image.

if sklearn_image_spec.is_container():
    from sklearn.linear_model import LogisticRegression

To enable tasks to utilize the images built with ImageSpec, you can specify the container_image parameter for those tasks.

def get_pandas_dataframe() -> typing.Tuple[pd.DataFrame, pd.Series]:
    df = pd.read_csv("")
    return df[["age", "thalach", "trestbps", "chol", "oldpeak"]], df.pop("target")

@task(container_image=sklearn_image_spec, requests=Resources(cpu="1", mem="1Gi"))
def get_model(max_iter: int, multi_class: str) -> typing.Any:
    return LogisticRegression(max_iter=max_iter, multi_class=multi_class)

# Get a basic model to train.
@task(container_image=sklearn_image_spec, requests=Resources(cpu="1", mem="1Gi"))
def train_model(model: typing.Any, feature: pd.DataFrame, target: pd.Series) -> typing.Any:, target)
    return model

# Lastly, let's define a workflow to capture the dependencies between the tasks.
def wf():
    feature, target = get_pandas_dataframe()
    model = get_model(max_iter=3000, multi_class="auto")
    train_model(model=model, feature=feature, target=target)

if __name__ == "__main__":

There exists an option to override the container image by providing an Image Spec YAML file to the pyflyte run or pyflyte register command. This allows for greater flexibility in specifying a custom container image. For example:

# imageSpec.yaml
python_version: 3.11
registry: pingsutw
  - sklearn
  Debug: "True"
# Use pyflyte to register the workflow
pyflyte run --remote --image image.yaml wf

If you only want to build the image without registering the workflow, you can use the pyflyte build command.

pyflyte build --remote wf