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<@ULVA73B9P> I've been following the <ECS Worker Guide> to get our infrastructure setup. Everything ...
# marvin-in-the-wild
j
@Marvin I've been following the ECS Worker Guide to get our infrastructure setup. Everything seems to be working fine except when I trigger a flow-run, it crashes and I don't get any logging in either the Prefect UI or in the ECS task. A couple things I've noticed: 1. The taskdef generated by the Prefect worker doesn't contain the prefect api url as an env var. Seems like it should: How does the worker pass this info to the flow task? 2. The taskdef generated by the Prefect worker doesn't have any logging setup. 3. The taskdef generated by the Prefect worker doesn't have any 
command
to customize how the docker container should be run... How does it know to run the specific flow? 4. When I run the docker image (locally) that is generated by the prefect cli, it doesn't actually run the flow... it just opens a shell prompt.
✅ 1
m
It seems there was an error retrieving the latest Prefect version automatically. I'll address your concerns based on the typical setup for Prefect, focusing on recent stable versions you might have encountered, such as Prefect 2.x or 3.x. 1. Environment Variable for Prefect API URL: In general, Prefect workers pass configuration information to tasks using environment variables. If the Prefect API URL is not being set, you might want to customize the ECS task definition manually or ensure your worker and agent are configured correctly to propagate this environment variable. Double-check your worker configuration or look for any Prefect settings specific to environment handling. 2. Logging Setup: If the generated task definition doesn't include logging, you may need to manually adjust the logging configuration in the task definition or through your AWS setup. Prefect typically relies on the underlying service (e.g., ECS or Kubernetes) to handle logs, so the integration must be set up correctly. Ensure that your ECS tasks are configured to send logs to a log group in CloudWatch or any preferred log storage solution. 3. Command for Running Flows: Prefect workers generally know how to run specific flows using environment variables and preset commands. The command that runs the flow is typically part of the Docker image's entry point. If it's just dropping you into a shell, there might be an issue with how the Docker image or the flow run command is configured. Verify that the entry point is set up to run Prefect flows. 4. Local Docker Run Issues: When running your Prefect Docker image locally, ensure it is properly configured to execute the flow by default. If it opens a shell prompt, you might need to manually specify the command to execute the flow or check the Dockerfile to ensure the correct behavior. For further investigation, please ensure that you are referencing the correct version of the Prefect documentation and the ECS guide. I'll make another attempt to fetch the specific documentation based on your scenario if needed. Can you confirm your Prefect version for a more precise follow-up?
j
@Marvin we're using Prefect 3. In the docker image what should the command to execute the flow look like?
m
In Prefect 3, if you're building a Docker image to execute a flow, your Dockerfile should be configured to include the appropriate command to run the flow. Here's an example approach to create a Docker image and execute the flow: 1. Dockerfile Setup: - Use the Prefect base image. - Copy your flow script and any dependencies. - Set up the command to execute the flow. Here's a sample Dockerfile that aligns with executing a Python script using Prefect:
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FROM prefecthq/prefect:2-python3.12-conda

RUN mkdir /usr/src/app
COPY your-flow.py /usr/src/app
COPY requirements.txt /usr/src/app
WORKDIR /usr/src/app
RUN pip install -r requirements.txt

CMD ["python", "./your-flow.py"]
2. Command Explanation: - 
CMD ["python", "./your-flow.py"]
specifies the command that Docker will run when the container starts. It should point to the script containing your Prefect flow. This setup ensures that once the container is running, it will execute the specified script where your Prefect flow is defined. Make sure to replace 
your-flow.py
with your actual flow script name. If your flows require other configurations or environment variables, be sure to include them in your Dockerfile or setup. For more information, you can check the Prefect 3 documentation about Docker deployments here.
j
@Marvin how do I specifiy a custom dockerfile when running 
prefect deploy
?
m
To specify a custom Dockerfile when using 
prefect deploy
, you can make use of the 
DockerImage
class to define your custom Docker image parameters, including the path to your Dockerfile. Here's how you can do it in Prefect 3: 1. Using the 
DockerImage
Class: - You will create a deployment configuration in which you use the 
DockerImage
class to point to your custom Dockerfile. Here's an example setup:
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python
from prefect import flow
from prefect.docker import DockerImage

@flow(log_prints=True)
def my_flow():
    print("Running my flow")

if __name__ == "__main__":
    my_flow.deploy(
        name="my-custom-dockerfile-deployment",
        work_pool_name="my-docker-pool",
        image=DockerImage(
            name="my_image",
            tag="deploy-guide",
            dockerfile="path/to/your/Dockerfile"
        ),
        push=False
    )
2. Explanation: - `name`: The name of your deployment. - `work_pool_name`: The work pool where the flow should run. - `image`: Configuration for the Docker image using the 
DockerImage
class. - 
name
and 
tag
for the Docker image. - `dockerfile`: Specify the path to your custom Dockerfile. - `push`: Set to 
False
if you don't want to push the image to a registry automatically. Make sure your Dockerfile is correctly set up at the specified path, and all the necessary dependencies and scripts are included. For more details, you might want to visit the Prefect 3 documentation on Docker deployments.
To specify a custom Dockerfile when using 
prefect deploy
in Prefect 3, you configure your deployment to use the 
DockerImage
class, pointing to your Dockerfile. Here's a step-by-step guide to help you with this: 1. Define Your Custom Dockerfile: Ensure you have a 
Dockerfile
ready with the necessary instructions to build your flow's environment. 2. Prefect Deployment with Custom Dockerfile: Create a deployment script or modify your deployment setup to include the 
DockerImage
configuration. Here's a simple example to illustrate how you can specify a custom Dockerfile when deploying a Prefect flow:
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python
from prefect import flow
from prefect.deployments import Deployment
from prefect.infrastructure.docker import DockerContainer

# Define your Prefect flow
@flow
def my_flow():
    print("This is my flow.")

# Create a DockerContainer infrastructure with a custom Dockerfile
docker_container = DockerContainer(
    image="my_custom_image:latest",
    dockerfile="path/to/your/Dockerfile"  # Path to your custom Dockerfile
)

# Create a deployment with the custom DockerContainer infrastructure
deployment = Deployment.build_from_flow(
    flow=my_flow,
    name="my-flow-deployment",
    infrastructure=docker_container
)

if __name__ == "__main__":
    deployment.apply()
3. Key Components: - 
DockerContainer
: Use this to configure your Docker container settings. - 
dockerfile
: Specify the path to your Dockerfile. - 
Deployment.build_from_flow
: Create a deployment specifying your flow and the custom Docker infrastructure. By following this setup, you ensure that your Prefect deployment uses the custom Dockerfile, allowing you to control the environment in which your flow executes. For more detailed guidance, refer to Prefect 3 documentation or articles related to Docker deployments.
k
are you building the image locally?
j
Yes, using the prefect cli right now
k
and if so, are you on a machine with an ARM chip like an M1 or newer mac?
j
Yes
k
can you add 
{"platform": "linux/amd64"}
to your build kwargs
if you're not sure where to put that you can paste your deployment code/config and I'll show you where it goes
j
I'm using 
prefect.yaml
right now.
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name: prefect_poc
prefect-version: 3.0.3

# build section allows you to manage and build docker images
build:
  - prefect_docker.deployments.steps.build_docker_image:
      id: build_image
      requires: prefect-docker>=0.3.1
      image_name: <http://738296499320.dkr.ecr.us-east-1.amazonaws.com/prefect-poc/flows|738296499320.dkr.ecr.us-east-1.amazonaws.com/prefect-poc/flows>
      tag: latest
      dockerfile: "Dockerfile"

# push section allows you to manage if and how this project is uploaded to remote locations
push:
  - prefect_docker.deployments.steps.push_docker_image:
      requires: prefect-docker>=0.3.1
      image_name: "{{ build_image.image_name }}"
      tag: "{{ build_image.tag }}"

# pull section allows you to provide instructions for cloning this project in remote locations
pull:
  - prefect.deployments.steps.set_working_directory:
      directory: /opt/prefect/prefect_poc

# the deployments section allows you to provide configuration for deploying flows
deployments:
  - name: hello-ecs-deployment
    version: "0.1"
    tags: []
    description:
    entrypoint: src/prefect_poc/hello_ecs_flow.py:my_flow
    parameters: {}
    work_pool:
      name: my-ecs-pool
      work_queue_name:
      job_variables:
      image: "{{ build_image.image }}"
    schedules: []
    concurrency_limit:
    enforce_parameter_schema: true
k
Copy code
prefect_docker.deployments.steps.build_docker_image:
      id: build_image
      requires: prefect-docker>=0.3.1
      image_name: <http://738296499320.dkr.ecr.us-east-1.amazonaws.com/prefect-poc/flows|738296499320.dkr.ecr.us-east-1.amazonaws.com/prefect-poc/flows>
      tag: latest
      dockerfile: "Dockerfile"
      platform: linux/amd64
j
Thanks will try!
✅ 1
@Kevin Grismore That worked! I'm getting the logging output in the Prefect UI. Do you know how to customize the deployment (or workpool, I guess) to setup cloudwatch logging for a flow-run?
k
if you go to edit the work pool, there's a bool option for that, which you can further customize
j
🚀
Thank you so much!!
k
no problem!!
j
@Kevin Grismore one more question: I had to add a 
CMD
to my dockerfile to get it to work. Seems strange... I would have expected the worker to set the 
command
in the task def. Is this expected?
CMD ["python", "./src/prefect_poc/hello_ecs_flow.py"]
k
yeah, your dockerfile shouldn't need a CMD in it at all
the default command is 
prefect flow-run execute
, which will start the engine and find the flow run id env var
j
Here is the 
Dockerfile
that prefect generated:
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FROM prefecthq/prefect:3.0.4-python3.12
COPY . /opt/prefect/prefect_poc/
WORKDIR /opt/prefect/prefect_poc/
Look right?
k
assuming you don't have a requirements.txt file, and your entrypoint picks up where that workdir leaves off, then yeah
j
Just so I understand how this should work: 1. Build the plain docker file (like above) and push to image repo (ECR) 2. Create the deployment on the Prefect Server 3. Create a worker that polls a work pool 4. Create a flow run from the deployment 5. Worker picks that up and creates a task def, then starts an ECS task from that task def. The task def should have the job id in the environment and it should pull the job details from the Prefect server?
k
that's right!
well. the one edit I'd make is that the worker gets the id, reads the deployment config from the server, then builds the task def and task run request using that info
j
Gotcha
So, looking the generated task def: I don't see the env vars I would expect:
Copy code
"containerDefinitions": [
        {
            "name": "prefect",
            "image": "<http://738296499320.dkr.ecr.us-east-1.amazonaws.com/prefect-poc/flows:latest|738296499320.dkr.ecr.us-east-1.amazonaws.com/prefect-poc/flows:latest>",
            "cpu": 0,
            "portMappings": [],
            "essential": true,
            "environment": [],
            "mountPoints": [],
            "volumesFrom": [],
            "systemControls": []
        }
    ],
oh, it uses tags!
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