@Marvin I am using Prefect 2.x and deploying from a prefect.yaml file. My flows run using the prefect-worker on kubernetes, so the flows start up in a container. Can you help me write a “pull” configuration that will do the following: • Clone a git repository, using a branch name that is passed in as some sort of parameter. Perhaps an environment variable set in the job variables named LIBRARY_VERSION. If there is a better way, please describe it. • If the parameter is NOT present, I do not need to clone the git repository. • Configure the executing Python flow code, which is is a library that the flow depends on, not the flow code itself, to use this source code to override the installed version of the library. Here are two examples of how I want my flow execution to work: 1. The user sets the environment variable LIBRARY_BRANCH in the job variables “env” value. The flow container starts up and fetches the library code from the branch in a github code repository. It then configures the Python execution to use this local source tree for any reference to the library in the flow code. The flow entry point is executed. 2. A flow container starts up, there is no value set for LIBRARY_BRANCH, so the flow code is executed normally. Please explain how to point to a local source code version of a python library as part of your answer.

To accomplish your goal with Prefect 2.x, you can set up your

prefect.yaml

file to use a "pull" configuration that clones a git repository if an environment variable is present. Here are the step-by-step instructions: 1. Environment Variable Setup: Ensure that your Kubernetes job is set up to include the environment variable

LIBRARY_BRANCH

when it's present. 2. Prefect YAML Configuration: Define the pull step in your

prefect.yaml

file to clone a git repository based on an environment variable, and adjust the Python path to use the cloned library if the branch is specified. Here is an example configuration:

yaml
# Welcome to your prefect.yaml file! You can use this file to manage
# configuration for deploying your flows. We recommend committing this file to source
# control along with your flow code.

# Generic metadata about this project
name: im30_rewards_autosubscriber_prefect
prefect-version: 2.x

# build section allows you to manage and build docker images
build: null

# push section allows you to manage if and how this project is uploaded to remote locations
push: null

# pull section allows you to provide instructions for cloning this project in remote locations
pull:
  - prefect.deployments.steps.git_clone:
      repository: <https://github.com/your-repo.git>
      branch: "{{ env.LIBRARY_BRANCH | default('main', true) }}"
      directory: "/opt/prefect/workspace/cloned-repo"

# the deployments section allows you to provide configuration for deploying flows
deployments:
  - name: my_flow
    entrypoint: "<http://path.to:flow_function|path.to:flow_function>"
    pull:
      - script: |
          export LIBRARY_BRANCH=${LIBRARY_BRANCH:-}
          if [ -n "$LIBRARY_BRANCH" ]; then
              echo "Cloning library from branch $LIBRARY_BRANCH"
              git clone -b "$LIBRARY_BRANCH" <https://github.com/your-repo.git> /opt/prefect/workspace/cloned-repo
              export PYTHONPATH=/opt/prefect/workspace/cloned-repo:$PYTHONPATH
          else
              echo "No library branch specified; proceeding without cloning."
          fi

### How it works: - Pull Configuration: The

pull

section defines the steps to be executed to prepare the environment before the flow runs. This setup clones the repo if the

LIBRARY_BRANCH

environment variable is set. - Script Step: The

script

step executes a shell script that checks if

LIBRARY_BRANCH

is set, clones the repo if true, and modifies the

PYTHONPATH

to include the cloned repository so that it overrides any installed library version. ### Clone the repo and set up the path dynamically: 1. Without Branch Specification: If no branch is specified (

LIBRARY_BRANCH

is empty or not set), the code runs as normal. 2. With Branch Specification: If

LIBRARY_BRANCH

is set, the script clones the specified branch of the repository and ensures that Python uses that version of the code. ### Additional Notes: - Ensure that the necessary environment variables are injected into the Kubernetes job where the Prefect worker runs. - You might need to modify directory paths if your setup requires different paths. This approach helps you achieve dynamic library version overriding in your Prefect 2.x deployment. For further details, refer to Prefect 2.x Documentation and specific GitHub Issues. If you need further specifics or have more questions, feel free to ask!

@Marvin That is very close to what I want. Why do I need to have the global “pull” definition in the prefect.yaml? This looks like it will always clone some branch of the library git repository. I do not want to do any git operation if the LIBRARY_VERSON is not set.

You are correct. The global pull configuration in

prefect.yaml

applies every time, which isn’t what you want. Here’s a refined approach where you use a conditional, checking for the presence of the

LIBRARY_BRANCH

environment variable at runtime: 1. Prefect YAML Configuration: We'll avoid setting a global pull step and use an entrypoint script that conditionally clones the git repository based on the presence of the environment variable.

yaml
# Welcome to your prefect.yaml file! You can use this file to manage
# configuration for deploying your flows. We recommend committing this file to source
# control along with your flow code.

# Generic metadata about this project
name: im30_rewards_autosubscriber_prefect
prefect-version: 2.x

# build section allows you to manage and build docker images
build: null

# push section allows you to manage if and how this project is uploaded to remote locations
push: null

# the deployments section allows you to provide configuration for deploying flows
deployments:
  - name: my_flow
    entrypoint: "entrypoint.sh"
    parameters: {}

2. Entrypoint Script: Create an entrypoint script (

entrypoint.sh

) that will handle the conditional cloning and then execute the flow.

bash
#!/bin/bash

# Check if LIBRARY_BRANCH is set and clone the repository if it is
if [ -n "$LIBRARY_BRANCH" ]; then
  echo "Cloning library from branch $LIBRARY_BRANCH"
  git clone -b "$LIBRARY_BRANCH" <https://github.com/your-repo.git> /opt/prefect/workspace/cloned-repo
  export PYTHONPATH=/opt/prefect/workspace/cloned-repo:$PYTHONPATH
else
  echo "No library branch specified; proceeding without cloning."
fi

# Execute the flow
python -m path.to.flow_function

3. Environment Variables in Kubernetes: Define the

LIBRARY_BRANCH

environment variable within your Kubernetes job spec when you need to override the library. Here's an example snippet of the Kubernetes job spec:

yaml
apiVersion: batch/v1
kind: Job
metadata:
  name: prefect-job
spec:
  template:
    spec:
      containers:
      - name: prefect-container
        image: your-prefect-image
        env:
        - name: LIBRARY_BRANCH
          value: "your-branch-name" # Set this when you want to override
        command: ["/bin/bash"]
        args: ["-c", "/opt/prefect/workflow/entrypoint.sh"]

### Overview 1. Conditional Clone: - The

entrypoint.sh

script checks if the

LIBRARY_BRANCH

environment variable is set. - If set, it clones the specified branch and updates

PYTHONPATH

. - If not set, it skips cloning. 2. Flow Execution: - After handling the library repository, the script runs your flow entry point. 3. Flexibility: - You can control whether the library gets cloned by simply setting or not setting the

LIBRARY_BRANCH

variable in your Kubernetes job configuration. This setup provides the conditional logic you need and keeps your

prefect.yaml

file neat. Feel free to ask if you need further details or assistance!

@Marvin OK, I would set the LIBRARY_VERSION environment variable in the “Job Variables” for my flow run since the prefect-worker creates the Kubernetes job spec. Is there any way to take the value of LIBRARY_VERSION as a flow parameter? Do I have access to flow parameters entered in to the Prefect UI when running a flow in the “pull” section of the deployment yaml?

You can use Prefect flow parameters within the

prefect.yaml

deployment file, and it is possible to access these parameters in the flow. However, using them directly in a pull step is a bit tricky since the pull section executes before the flow parameters are actually processed. Here’s how you can achieve your goal: 1. Define Flow Parameters in Prefect: Specify the

LIBRARY_VERSION

as a flow parameter in your Prefect backend. 2. Retrieve Parameter in Flow: Access the flow parameter within the flow and perform the clone operation there, rather than in the pull section. Here’s an example configuration: ### Prefect YAML Configuration: We'll define the flow parameter in the

prefect.yaml

.

yaml
# The deployments section allows you to provide configuration for deploying flows
deployments:
  - name: my_flow
    entrypoint: "<http://path.to:flow_function|path.to:flow_function>"
    parameters:
      LIBRARY_VERSION: "default-branch"  # This is the default value

### Flow Code: Include logic in your flow to clone the repository based on the flow parameter

LIBRARY_VERSION

.

python
import prefect
from prefect import flow, task
import os
import subprocess

@task
def clone_library(library_version: str):
    if library_version:
        print(f"Cloning library from branch {library_version}")
        subprocess.run(['git', 'clone', '-b', library_version, '<https://github.com/your-repo.git>', '/opt/prefect/workspace/cloned-repo'], check=True)
        os.environ['PYTHONPATH'] = f"/opt/prefect/workspace/cloned-repo:{os.getenv('PYTHONPATH', '')}"
    else:
        print("No library branch specified; proceeding without cloning.")

@flow
def flow_function(LIBRARY_VERSION: str):
    clone_library(LIBRARY_VERSION)
    # Add your flow logic here

if __name__ == '__main__':
    flow_function()

### Usage: 1. Default Run: - If you simply run the flow without specifying the parameter, it will use the default branch specified in the

prefect.yaml

. 2. Custom Run via Prefect UI: - You can override the

LIBRARY_VERSION

when creating an ad-hoc run through the Prefect UI. - When starting the flow run, set the

LIBRARY_VERSION

to the desired branch name in the parameters section. ### Additional Notes: - This approach ensures that the cloning logic is part of the flow execution and respects the parameter passed at runtime. - By using the Prefect UI, users can set the

LIBRARY_VERSION

parameter interactively, offering greater flexibility. This setup helps achieve the dynamic behavior you need without embedding conditional git operations in the

prefect.yaml

pull steps. Let me know if you need further clarification or assistance!