Hello < Marvin> I have a flow packaged into a docker image t Prefect Community #ask-marvin

Hello <@ULVA73B9P>. I have a flow packaged into a ...

Alan

03/21/2024, 9:58 PM

Hello @Marvin. I have a flow packaged into a docker image that is being used inside a docker worker. I am getting this error when I trigger the flow from the dashboard:

Copy code

Traceback (most recent call last):
  File "/opt/anaconda/lib/python3.11/site-packages/prefect/engine.py", line 458, in retrieve_flow_then_begin_flow_run
    parameters = flow.validate_parameters(flow_run.parameters)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/anaconda/lib/python3.11/site-packages/prefect/flows.py", line 559, in validate_parameters
    raise ParameterTypeError.from_validation_error(exc) from None
prefect.exceptions.ParameterTypeError: Flow run received invalid parameters:
 - environment: Field required

Question is how do I ensure that the parameters reach the flow in my dockerfile?

Marvin

03/21/2024, 9:58 PM

To ensure that the parameters reach the flow inside your Docker container, you will typically set environment variables in your Dockerfile or pass them as command-line arguments when starting your Docker container. Here are some steps you can follow: 1. Set environment variables in the Dockerfile: You can define the environment variables in your Dockerfile using the

ENV

instruction. For example, if you need to pass a parameter named "environment", you can set it in your Dockerfile like this:

Copy code

Dockerfile
   ENV environment=default_value

Replace

default_value

with the actual value you want to set. 2. Pass environment variables during
docker run
: You can also pass the environment variables when running your container using the

-e

--env

option:

Copy code

bash
   docker run -e environment=value my-docker-image

Again, replace

value

with the actual value you want to pass to the parameter. Additionally, if you're using Prefect deployments to orchestrate your flows, you might need to consider how parameters are set up during the deployment process. For instance, you might pass parameters while triggering the flow run from the Prefect dashboard or API. Here's some useful documentation and an example for your reference: - Setting environment variables for Docker and connecting to the Prefect API: - Guide on using Docker with Prefect - Understanding infrastructure with Prefect - Prefect code example related to setting parameters: - Basic Prefect flow example (This example does not provide specifics on setting parameters for Docker; it is a generic Python code example using Prefect) Make sure to adjust your Dockerfile and Docker run commands to include the required parameters as environment variables, and check if your Prefect deployment configuration requires any specific settings for parameters to be passed effectively.

Alan

03/22/2024, 4:29 AM

@Marvin where will the dockerfile get the parameters if the run is triggered from prefect dashboard? will the prefect worker have them?

Marvin

03/22/2024, 4:29 AM

When triggering a flow run from the Prefect dashboard, you would typically set parameters during the flow run creation process. These parameters are then stored within the flow run metadata and will be passed to the flow when it starts executing. The Docker worker that picks up the flow run will not necessarily have the parameters directly; instead, they are conveyed as part of the flow run context. That means the flow, when executed inside the Docker container, retrieves the parameters from the Prefect API or the internal metadata store, depending on how Prefect is set up. For Prefect Cloud (and similar for Prefect Server), you can also utilize deployment triggers with parameter templating. This allows you to pass event data into the deployment run as parameters through templates. Here are the documents related to this information: - Triggering flows with deployment triggers and parameters in Prefect Cloud - Specifying infrastructure for flow runs via the UI In other words, your Dockerfile doesn't have to handle the parameters directly; they are managed by Prefect and provided to the running flow. When configuring your Docker infrastructure for Prefect, make sure you grant the flow access to the Prefect API and set up any necessary authentication or configuration so it can retrieve parameters and other necessary metadata for the flow run.

Alan

03/22/2024, 4:33 AM

@Marvin so the docker worker I have connects to the prefect api server and pulls the image stipulated in the deployment and is able to run the docker image. My question is, is it sufficient to include the variable as follows in the docker image?

Copy code

Dockerfile
   ENV environment

# Run our flow script when the container starts
CMD ["python", "flows/flow.py", "-e", "environment"]

Marvin

03/22/2024, 4:34 AM

Defining an environment variable without a value in your Dockerfile using the

ENV

instruction (e.g.,

ENV environment

) will not set the variable to any value within the container. Instead, this would typically be used to provide a default value or to signal that the environment variable is expected to be provided at runtime. To provide the actual value for

environment

, you should do this when you run the container:

Copy code

bash
docker run -e environment=value my-docker-image

Where

value

is the actual value you want to associate with the

environment

variable. Regarding the

CMD

in your Dockerfile, normally, the command used to initiate a Prefect flow run does not need to pass environment variables as arguments. Prefect typically manages parameters through its own mechanisms (like the Prefect API). Your flow script would generally use Prefect’s API or context to access the parameters. Here’s an excerpt from the Prefect documentation on DockerContainer infrastructure, which describes the

env

attribute: - Prefect DockerContainer Infrastructure The

env

attribute within infrastructure definitions is used for setting environment variables for the new process that runs the flow. In summary, while you may define placeholders for environment variables in your Dockerfile, the actual values are typically passed at runtime using

-e

flags when running the container, or they are provided by Prefect when it sets up the flow run in the container. Your flow script should be written to retrieve and use these values from the environment using standard Python methods for accessing environment variables, such as

os.environ

Alan

03/22/2024, 4:38 AM

@Marvin my parameters showing in the prefect dashboard are:

Copy code

inspection_id		string
storage_url			string
environment         string

are you saying that in my flow.py script which is packaged into the docker container should access them via:

Copy code

inspection_id = os.environ["inspection_id"]
storage_url = os.environ["storage_url"]
environment = os.enviro["environment"]

Marvin

03/22/2024, 4:39 AM

Based on the information provided, if the parameters for your Prefect flow are being set in the dashboard, you would typically access them using Prefect's

Parameter

functionality within your flow definition, rather than directly accessing them via environment variables. Here's an example of how you might define a flow with parameters:

Copy code

python
from prefect import flow, task
from prefect.parameters import String

@task
def some_task(param):
    # Do something with the param
    print(param)

@flow
def my_flow(inspection_id: String(), storage_url: String(), environment: String()):
    some_task(inspection_id)
    some_task(storage_url)
    some_task(environment)

if __name__ == "__main__":
    my_flow()

However, if you are passing the parameters as environment variables when running the Docker container (using

-e

flags, for instance), then you would access them using the

os.environ

dictionary as you mentioned:

Copy code

python
import os

inspection_id = os.environ["inspection_id"]
storage_url = os.environ["storage_url"]
environment = os.environ["environment"]

Ensure you are consistent with how you are setting and accessing parameters within your flow. If parameters are set via the Prefect dashboard, use the

Parameter

class unless you've set up a specific mechanism to populate the environment variables of your Docker container with those values. If you're setting them through Docker environment variables, your approach would be correct. Keep in mind, Prefect expects parameters to be defined and accessed in the way specified by its flow and task APIs.

3 Views

Open in Slack

Previous Next