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<@ULVA73B9P> it is possible to store the name of a...
# ask-marvin
a
@Marvin it is possible to store the name of a block as an environment variable?
m
Hmm, detecting the right bits in this universe is as easy as finding a needle in a stack of other needles. 1. It appears there is no direct mention in the documentation or relevant issues about storing the name of a block as an environment variable directly. 2. For the ECSTask block, environment variables can be defined as part of the block configuration on the "environment" attribute. I suggest you configure the block to include desired environment variables during its setup. If you need more guidance on configuring blocks and environment variables, you could check Prefect Documentation or open a GitHub Issue for more specific guidance. If this answer is depressing, it wouldn't surprise me... Would you have more questions or need further assistance?
a
@Marvin how can I dynamically pick a block to use when defining a work pool in prefect.yaml based on the value of an environment variable
m
It seems that dynamically picking a block based on the value of an environment variable directly in the 
prefect.yaml
isn't documented or discussed explicitly in issues. However, I can suggest a potential solution using Python to dynamically determine the block and then use it in your deployment. 1. Define the Environment Variable: Export your desired environment variable before running your deployment.
Copy code
shell
   export MY_BLOCK_NAME=<block_name>
2. Python Script to Dynamically Pick the Block: Create a Python script that reads the environment variable and applies the required logic to pick the block. 3. Dynamically Generate your Deployment: Use the environment variable to select the block and then configure the deployment.
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python
import os
from prefect.deployments import Deployment
from prefect.infrastructure import DockerContainer  # or your chosen infrastructure

# Read the environment variable
block_name = os.getenv('MY_BLOCK_NAME')

# Dynamically create a block, here using DockerContainer as an example
infrastructure_block = DockerContainer.load(block_name)

# Define your deployment with the dynamically selected infrastructure block
deployment = Deployment.build_from_flow(
    name="dynamic-block-deployment",
    flow=my_flow,
    infrastructure=infrastructure_block
)

# Apply the deployment
deployment.apply()
Save the above script and run it to dynamically configure your deployment based on the environment variable. Well, even in the face of this unbearable code-driven universe, I hope this method helps you out. If you need further assistance, feel free to ask—though I'm certain whatever it is, it'll just add to my already infinite list of complaints.
a
@Marvin I’d like to do the same thing but in the prefect.yaml file
m
The documentation and code examples did not reveal a direct way to dynamically select a block in 
prefect.yaml
based on environment variables. However, you can achieve a similar effect by using YAML templating with Jinja2 and a Python script to render the final 
prefect.yaml
. Here's how you can do it: 1. Create a Template for 
prefect.yaml
: Define your 
prefect.yaml
template file (
prefect_template.yaml
):
Copy code
yaml
   version: "2.0"

   flows:
     - name: your-flow-name
       parameters: {}
       infra_overrides:
         block: "{{ block_name }}"
2. Create a Python Script to Render the Template: Use Python to read the environment variable, render the template with Jinja2, and output the final 
prefect.yaml
file.
Copy code
python
   import os
   from jinja2 import Environment, FileSystemLoader

   # Load the environment variable
   block_name = os.getenv('MY_BLOCK_NAME', 'default-block-name')

   # Set up Jinja2 environment
   env = Environment(loader=FileSystemLoader('.'))
   template = env.get_template('prefect_template.yaml')

   # Render the template with the block_name
   rendered_yaml = template.render(block_name=block_name)

   # Output the rendered template to prefect.yaml
   with open('prefect.yaml', 'w') as f:
       f.write(rendered_yaml)

   print("prefect.yaml has been generated with block:", block_name)
3. Generate the Final 
prefect.yaml
: Run your script to render the template and generate the `prefect.yaml`:
Copy code
shell
   python render_prefect_yaml.py
By doing this, the script will dynamically pick the block name based on the value of the environment variable and generate the 
prefect.yaml
accordingly. I know, it's tedious, but such is existence when dynamic configuration is imperative. If you need further refinement or assistance, don't hesitate to ask.
a
@Marvin can I use environment variables when naming a flow in prefect.yaml?
m
Based on the searches through documentation and GitHub issues, there isn't a direct way to use environment variables when naming a flow in the 
prefect.yaml
file. However, similar to dynamically configuring blocks, you can use Jinja2 templating to achieve this. Here's a step-by-step workaround: 1. Create a Template for 
prefect.yaml
: Define your 
prefect.yaml
template file (
prefect_template.yaml
):
Copy code
yaml
   version: "2.0"

   flows:
     - name: "{{ flow_name }}"
       parameters: {}
       infra_overrides:
         block: "some_block"
2. Create a Python Script to Render the Template: Use Python to read the environment variable, render the template with Jinja2, and output the final 
prefect.yaml
file.
Copy code
python
   import os
   from jinja2 import Environment, FileSystemLoader

   # Load the environment variable
   flow_name = os.getenv('FLOW_NAME', 'default-flow-name')

   # Set up Jinja2 environment
   env = Environment(loader=FileSystemLoader('.'))
   template = env.get_template('prefect_template.yaml')

   # Render the template with the flow_name
   rendered_yaml = template.render(flow_name=flow_name)

   # Output the rendered template to prefect.yaml
   with open('prefect.yaml', 'w') as f:
       f.write(rendered_yaml)

   print("prefect.yaml has been generated with flow name:", flow_name)
3. Generate the Final 
prefect.yaml
: Run your script to render the template and generate the `prefect.yaml`:
Copy code
shell
   python render_prefect_yaml.py
By using this approach, you can dynamically set the flow name in your 
prefect.yaml
file based on the value of an environment variable. Admittedly, it requires slightly more effort, but at least it brings some dynamic aspect into your Prefect configuration. If you require further guidance or have additional questions, I am here—though I ponder why it always ends up like this...
a
@Marvin can I do this directly in the prefect.yaml file?
m
Again, the available resources didn't precisely address using environment variables directly in the 
prefect.yaml
file for naming flows. Currently, it seems there isn't a built-in feature in Prefect to directly substitute environment variables in the 
prefect.yaml
. The workaround, as previously mentioned, involves using a Jinja2 template along with a Python script to achieve dynamic configuration. This method allows you to harness the flexibility of Jinja2 templating to set the flow name based on an environment variable. Here’s a simplified recap of the steps: 1. Create a Template for 
prefect.yaml
: Define your 
prefect_template.yaml
file:
Copy code
yaml
   version: "2.0"

   flows:
     - name: "{{ flow_name }}"
       parameters: {}
       infra_overrides:
         block: "some_block"
2. Render the Template Using a Python Script: Use Python along with Jinja2 to render your 
prefect.yaml
file.
Copy code
python
   import os
   from jinja2 import Environment, FileSystemLoader

   # Use environment variable for the flow name
   flow_name = os.getenv('FLOW_NAME', 'default-flow-name')

   # Set up Jinja2 templatting
   env = Environment(loader=FileSystemLoader('.'))
   template = env.get_template('prefect_template.yaml')

   # Render the template
   rendered_yaml = template.render(flow_name=flow_name)

   # Write the result to prefect.yaml
   with open('prefect.yaml', 'w') as f:
       f.write(rendered_yaml)

   print(f"Generated prefect.yaml with flow name: {flow_name}")
3. Generate 
prefect.yaml
: Run your script:
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shell
   python script_name.py
I understand it's a bit roundabout, but this method effectively achieves dynamic configuration with environment variables. If Prefect introduces a direct way to use environment variables within 
prefect.yaml
in the future, it would certainly simplify this process. For now, this templating approach ensures you have the flexibility needed. If you need more specific help or have further questions, please let me know.
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