@Marvin I'm running on Push ECS infrastructure and i'm getting intermittent failures with the following messages: Do you know what might cause this issue?

Downloading flow code from storage at '.'
09:08:25 AM
prefect.flow_runs
Flow could not be retrieved from deployment.
Traceback (most recent call last):
  File "<frozen importlib._bootstrap_external>", line 846, in exec_module
  File "<frozen importlib._bootstrap_external>", line 982, in get_code
  File "<frozen importlib._bootstrap_external>", line 1039, in get_data
FileNotFoundError: [Errno 2] No such file or directory: 'scrapers/scraper_rookies_animation.py'

The above exception was the direct cause of the following exception:

  File "/home/prefect/.local/lib/python3.9/site-packages/prefect/utilities/importtools.py", line 168, in load_script_as_module
    raise ScriptError(user_exc=exc, path=path) from exc
prefect.exceptions.ScriptError: Script at 'scrapers/scraper_rookies_animation.py' encountered an exception: FileNotFoundError(2, 'No such file or directory')

So, you're saying it can't find the file for your flow. Let's find out why. What version of Prefect are you using?

@Marvin version 3.x

Based on what I've found, here are a few potential reasons why you're experiencing intermittent issues with retrieving flow code from storage on ECS: 1. Storage Location Configuration: Ensure that your storage location (e.g., an S3 bucket) is properly configured and the path to the flow code is correct. Any discrepancy here can cause

FileNotFoundError

. 2. Infrastructure Automation Command: When setting up infrastructure for ECS using the push method, Prefect automates much of the configuration. You can use:

prefect work-pool create --type ecs:push --provision-infra my-ecs-pool

This will help set up an ECS cluster that uses AWS Fargate, VPC, and an ECR repository if they don’t already exist. 3. AWS Permissions: Make sure you have the appropriate AWS permissions in place, like

AmazonECS_FullAccess

and

AmazonEC2ContainerRegistryFullAccess

. These permissions are essential for ECS to access flow code stored in S3 or similar services. 4. Code Storage: Double-check that your storage block for code retrieval (like an S3 bucket) is appropriately set up:

python
   from prefect_aws.s3 import S3Bucket
   flow.from_source(
       source=S3Bucket.load("my-code-storage"),
       entrypoint="flows.py:my_flow",
   )

More details can be found here: Store Flow Code For further reading on Prefect's ECS setup, visit the ECS Worker Guide. If these steps don't fix the issue, please provide more specific details about your setup, or consult the Prefect GitHub Issues for similar cases.

@Marvin It works "sometimes" - almost like the infrastucture isn't spun up on time so it fails.

Got it! Here's a more detailed way to address potential timing issues with your infrastructure setup on ECS: 1. Ensure ECS Task Readiness: Ensure ECS tasks are fully running before attempting to download the flow code. You can use AWS's ECS service events to check task status. 2. Retries and Delays: Add retry logic in your flow to handle transient issues during infrastructure spin-up.

python
   from prefect import flow, task

   @task(retries=3, retry_delay_seconds=30)
   def download_flow_code():
       # Your code to download the flow goes here
       pass

   @flow
   def my_flow():
       download_flow_code()

3. Custom Start-Up Scripts: Implement a start-up script that waits for the necessary infrastructure to be ready before starting the flow. This script can poll for the readiness of storage location or ECS task status. 4. Work Pool Configuration: Consider provisioning your ECS work pool manually and ensuring it is fully prepared before deploying your flow:

bash
   prefect work-pool create --type ecs:push --provision-infra my-ecs-pool

5. AWS CloudFormation: If your infrastructure is defined using AWS CloudFormation, ensure that all dependencies signal they are ready. Use

DependsOn

attribute to control the order of resource creation. 6. Health Checks and Pre-flight Checks: Before starting the main task, add health checks to ensure that all dependent systems are operational:

python
   import boto3
   from time import sleep

   def check_s3_bucket(bucket_name):
       s3 = boto3.client('s3')
       try:
           s3.head_bucket(Bucket=bucket_name)
           return True
       except:
           return False

   @task
   def preflight_checks():
       while not check_s3_bucket("my-bucket"):
           sleep(10)
       return True

   @flow
   def my_flow():
       preflight_checks()
       download_flow_code()

These strategies should help mitigate timing-related issues. If you continue to encounter difficulties, consider providing additional details or consulting resources such as the Prefect documentation or GitHub Issues to find similar cases and solutions.

@Marvin it's still having issues - what can I do to have it ensure that the container is ready before it tries to run it?

If the container is sometimes not ready before the flow attempts to run, you can take additional steps to ensure readiness: 1. Use Prefect's Health Check Tasks: Use Prefect tasks to implement health checks that confirm the necessary components are ready before executing the primary flow logic. 2. Custom ECS Task Definitions with Dependencies: Define dependencies in your ECS task definition to ensure that containers start in a specific order. 3. AWS CloudFormation Wait Condition: Use AWS CloudFormation with wait conditions to ensure that the infrastructure is ready before starting the ECS tasks. Here's how you might implement some of these strategies: ### 1. Prefect Health Check Task Implement a task that checks the availability of your ECS service before proceeding:

python
from prefect import flow, task
import boto3
from botocore.exceptions import ClientError
import time

@task(retries=3, retry_delay_seconds=30)
def check_ecs_service():
    client = boto3.client('ecs')
    try:
        response = client.describe_services(
            cluster='your-cluster-name',
            services=['your-service-name']
        )
        services = response.get('services', [])
        if services and services[0]['deployments'][0]['status'] == 'PRIMARY':
            return True
    except ClientError as e:
        return False

    return False

@flow
def my_flow():
    if check_ecs_service():
        # Your main flow logic here
        pass

if __name__ == "__main__":
    my_flow()

### 2. Custom ECS Task Definitions with Container Dependencies You can define container dependencies within your ECS task definition to ensure that supporting services are ready before the main container starts. Create a task definition JSON file:

json
{
  "family": "myTaskDefinition",
  "containerDefinitions": [
    {
      "name": "containerA",
      "image": "my-image",
      "essential": true,
      "dependsOn": [
        {
          "containerName": "containerB",
          "condition": "HEALTHY"
        }
      ]
    },
    {
      "name": "containerB",
      "image": "my-dependency-image",
      "essential": true,
      "healthCheck": {
        "command": ["CMD-SHELL", "curl -f <http://localhost/> || exit 1"],
        "interval": 30,
        "timeout": 5,
        "retries": 3,
        "startPeriod": 60
      }
    }
  ]
}

Register the task definition with ECS:

bash
aws ecs register-task-definition --cli-input-json <file://task-definition.json>

### 3. AWS CloudFormation Wait Condition Use a wait condition in your CloudFormation template to ensure resources are ready before proceeding. Here’s a simplified example:

yaml
Resources:
  MyBucket:
    Type: AWS::S3::Bucket

  WaitConditionHandle:
    Type: AWS::CloudFormation::WaitConditionHandle

  WaitCondition:
    Type: AWS::CloudFormation::WaitCondition
    DependsOn: MyBucket
    Properties:
      Handle: !Ref WaitConditionHandle
      Timeout: 300
      Count: 1

  MyService:
    Type: AWS::ECS::Service
    Properties:
      ...
    DependsOn: WaitCondition

### ECS Health Check on Container Start Ensure your ECS task definition has health checks defined to verify readiness before starting the main application. By combining these strategies, you can build a more robust setup that ensures your infrastructure is ready before running your flows. If issues persist, you may need to dig deeper into ECS task logs or contact AWS support for assistance with specific ECS stability or readiness concerns.

@Brian Roepke did you ever resolve this issue? I'm also getting the

Flow could not be retrieved from deployment.

Its random when it happens but we are also using Kubernetes, and the code exists on the customer Docker Container image we are using so no code needs to be pulled in.

Hi @Dave D - I did resolve this - I can't find the resolution right now, but what happened was I had an old work pool (Hybrid), and each of them had a Work Queue called "default" - this was causing a name collision where the old Hybrid one was trying to pick up the work, but that machine image didn't have the code (it was pulled from GitHub for those Flows) - so it gave me that error. You can see in the third image I created a new Queue called

fxdmz-ecs-queue,

and that cleared it up. Ever since correcting that, it has been flawless.

Thanks Brian!!! I'll try this out.

@Dave D Just for fun. Here is the full code for deployment at the entry point:

if __name__ == "__main__":
    scrape_rookies_animation_studios.deploy(
        name="scrape-rookies-animation-studios-ecs-deployment",
        work_pool_name="fxdmz-ecs-pool",
        work_queue_name="fxdmz-ecs-queue",
        build=False,
        push=False,
        image=DockerImage(
            name="<http://63XXXXXXXX88.dkr.ecr.us-east-1.amazonaws.com/prefect-flows:latest|63XXXXXXXX88.dkr.ecr.us-east-1.amazonaws.com/prefect-flows:latest>",
            platform="linux/amd64",
        ),
    )

@Brian Roepke very nice, i did something very similar. We were re-using the same queue name but had a different work pool name. I changed the deployment to use a brand new queue name with priority 1 on the new work pool. I also paused all old work pools and queues that were arent using anymore and 🤞 this is the answer.

Awesome! I hope it works! I read somewhere here, or in a doc that the name is what is referenced and not some internal UUID, so collisions can be expected. That's a bummer since everything creates "default" by "default." I hope this clears it up for you!

LOOKS GOOD! Thanks! I was really stressing about this. Thanks so much!