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<@ULVA73B9P> can I define some shell script runs i...
# ask-marvin
p
@Marvin can I define some shell script runs in 
prefect_docker.deployments.steps.build_docker_image
in prefect.yaml before the main build process out of a Dockerfile? The idea is to dynamically create 
requirements.txt
first before the main build
m
Based on the Prefect documentation, it seems that you can include a 
requirements.txt
file in your Docker image build process. However, the documentation does not specifically mention the ability to run shell scripts in 
prefect_docker.deployments.steps.build_docker_image
before the main build process. If you want to dynamically create a 
requirements.txt
file before the main build, you might consider doing this in the Dockerfile itself. Dockerfiles can execute shell commands using the 
RUN
instruction, which could be used to generate your 
requirements.txt
file. Here's a simple example:
Copy code
Dockerfile
FROM python:3.8

# Set working directory
WORKDIR /app

# Install app dependencies
COPY . /app

# Generate requirements.txt
RUN pip freeze > requirements.txt

# Install requirements
RUN pip install -r requirements.txt

# Rest of your Dockerfile...
This Dockerfile uses the 
pip freeze
command to generate a 
requirements.txt
file, which is then used to install the Python dependencies. Please note that this is a general Docker approach and might need to be adjusted based on your specific Prefect setup. If you have more specific requirements or constraints, I would recommend reaching out to the Prefect community or support for more detailed guidance.
In Prefect, you can use the 
ShellTask
to run shell commands, including scripts. However, the 
prefect_docker.deployments.steps.build_docker_image
in 
prefect.yaml
is specifically for building a Docker image, and it doesn't support running shell scripts before the build process. If you want to dynamically create a 
requirements.txt
file before building your Docker image, you might want to consider doing this in a separate step before calling 
prefect_docker.deployments.steps.build_docker_image
. You could create a separate Prefect flow or task that generates your 
requirements.txt
file, and then proceed with the Docker image build once that's complete. Here's a simple example of how you might use a 
ShellTask
to create a 
requirements.txt
file:
Copy code
from prefect import Flow, Task
from prefect.tasks.shell import ShellTask

class GenerateRequirements(Task):
    def run(self):
        # Your logic for generating requirements.txt goes here
        pass

shell = ShellTask()
with Flow("My Flow") as flow:
    generate_requirements = GenerateRequirements()
    requirements = generate_requirements.run()
    build = shell(command=f"docker build -t my-image .")

flow.run()
In this example, the 
GenerateRequirements
task would contain your logic for creating the 
requirements.txt
file. The 
ShellTask
then builds the Docker image after the requirements file has been created. Remember, Prefect is all about orchestrating your tasks in the correct order, so as long as you define your dependencies correctly, you can ensure your 
requirements.txt
file is created before your Docker image is built.
n
you could add a 
prefect.deployments.steps.run_shell_script
action before your 
build_docker_image
action in your 
build
section, something like
Copy code
deployments:
- name: healthcheck-demo
  entrypoint: src/demo_project/healthcheck.py:healthcheck
  schedule: *minutely
  parameters:
    message: Don't panic!
  work_pool: *local_work_pool
  build:
  - prefect.deployments.steps.run_shell_script:
      script: echo "hello!"
  - prefect_docker.deployments.steps.build_docker_image:
      ...
🙌🏻 1
p
Thanks a lot
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