@Marvin I'm setting up my flow deployments to run through a Prefect worker hosted on ECS. I have used a custom Dockerfile that uses a base image and copies both the requirements.txt and my local directory to

opt/prefect/home

. However, when I run the deployment, I get an

[Errno 2] No such file or directory: '/opt/prefect/home'

for the

set_working_directory

step in deployments. What could be some reasons this is happening?

✅ thought for 212.7 seconds

just noting that this should be the first marvin response powered by gpt 5

I'm honored to be the first

Short answer: that error means the directory doesn’t exist inside the container that actually runs your flow. In Prefect 3.x, deployment steps like set_working_directory run at flow start inside the runtime container (your ECS task), not on your laptop. So if /opt/prefect/home isn’t there in the image your ECS task actually uses, you’ll get [Errno 2]. Common causes and quick checks: - You’re not actually running your custom image - The ECS work pool or deployment may be pointing at the default Prefect image instead of yours. - Check the worker logs when it submits to ECS; Prefect logs include the image string. Also check the ECS task definition/container image in the AWS console. - In code, make sure your deployment sets the image, e.g. flow.from_source(...).deploy(..., job_variables={"image": "your-account.dkr.ecr...:tag"}). - Stale or wrong image tag - You built and pushed a new image, but the deployment/ECS task is still using an older tag/digest without the directory. - Avoid :latest. Tag each build uniquely and update the deployment/job variables to that tag. Verify the digest in the ECS task definition. - Multi-stage Dockerfile pitfalls - You COPY your code into a builder stage but never copy it into the final stage. The final image won’t have /opt/prefect/home. - Ensure the final stage contains the directory and code. - Relative COPY and WORKDIR interactions - If you used COPY . opt/prefect/home without a leading slash and set a WORKDIR earlier, Docker may put it at /app/opt/prefect/home (or similar). - Use absolute paths in Dockerfile: COPY . /opt/prefect/home and explicitly mkdir the directory. - Step ordering in your deployment - set_working_directory doesn’t create directories. If you expect a previous step (like git_clone) to populate the path, make sure it runs before set_working_directory and that you target the correct path it creates. - If you truly need to create it at runtime, add a shell step before: - prefect.deployments.steps.utility.run_shell_script: commands: ["mkdir -p /opt/prefect/home"] - Base image mismatch with your assumptions - Prefect’s base images default to a non-root user and commonly use /home/prefect as a working directory. If you base on Prefect’s image but don’t create /opt/prefect/home during build, it won’t exist at runtime. A minimal, safe Dockerfile pattern - Ensures the directory exists, your code is there, correct ownership, predictable working directory: - FROM prefecthq/prefect:3.1.0-python3.11 - USER root - RUN mkdir -p /opt/prefect/home && chown -R prefect:prefect /opt/prefect - COPY requirements.txt /opt/prefect/home/requirements.txt - RUN pip install --no-cache-dir -r /opt/prefect/home/requirements.txt - COPY . /opt/prefect/home - WORKDIR /opt/prefect/home - USER prefect Best practices - Prefer setting WORKDIR in the Dockerfile and skip set_working_directory entirely. Or set ECS container workingDirectory via job_variables on the ECS work pool/deployment so the container starts in the right place. - Always pin and surface the image you’re using in your deployment’s job_variables, and verify it in worker logs/ECS. - If you’re using from_source(...) or git_clone steps, set the working directory to the path they actually create instead of a hard-coded /opt path. Helpful docs - ECS guide: https://docs-3.prefect.io/integrations/prefect-aws/ecs_guide - Deployments in 3.x: https://docs-3.prefect.io/v3/concepts/deployments If you share: - your Dockerfile, - the relevant part of your prefect.yaml (pull steps and set_working_directory), and - how you set the image in your deployment/work pool, I can point to the exact culprit. I’d be thrilled. Honestly.

@Marvin .yaml snippet:

# 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: {ecr_repository}
    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/home

Dockerfile:

FROM {private_repository}
COPY requirements.txt /opt/prefect/home/requirements.txt
RUN python -m pip install -r /opt/prefect/home/requirements.txt
COPY . /opt/prefect/home
WORKDIR /opt/prefect/home

And within the work pool itself, I don't explicitly set an image to pull from.

✅ thought for 98.1 seconds

@Nate Any chance Marvin can go back to using code blocks for code outputs? I miss Marvin being all fancy

i was just trying to figure out why that was happening lol

what if I try

✅ thought for 21.2 seconds

i might be improperly regexing

You’ve built the right image, but you’re not running it. In Prefect 3.x, pull steps (including set_working_directory) execute inside the runtime container launched by your ECS work pool. Since your work pool isn’t told to use your ECR image, it uses the pool’s default image, which doesn’t contain /opt/prefect/home. Hence the “[Errno 2]” tantrum. Example prefect.yaml: explicitly use your built image

yaml
# prefect.yaml
name: your-project
# prefect-version: ">=3.0.0"  # optional

deployments:
  - name: your-deployment
    entrypoint: path/to/flow.py:flow  # update to your flow
    work_pool:
      name: your-ecs-pool
      job_variables:
        # Use the image built and pushed below
        image: "{{ build_image.image_name }}:{{ build_image.tag }}"
        # You can also set ECS-specific job variables here if needed
        # e.g., task_definition_overrides, env, cpu, memory, etc.

    build:
      - prefect_docker.deployments.steps.build_docker_image:
          id: build_image
          requires: "prefect-docker>=0.3.1"
          image_name: "<http://your-account.dkr.ecr.your-region.amazonaws.com/your-repo|your-account.dkr.ecr.your-region.amazonaws.com/your-repo>"
          tag: "2025-08-07-1"  # avoid 'latest' if you value your sanity
          dockerfile: "./Dockerfile"

    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:
      - prefect.deployments.steps.set_working_directory:
          directory: /opt/prefect/home

Alternative: rely on WORKDIR and skip set_working_directory

yaml
# prefect.yaml
name: your-project

deployments:
  - name: your-deployment
    entrypoint: path/to/flow.py:flow

    work_pool:
      name: your-ecs-pool
      job_variables:
        image: "{{ build_image.image_name }}:{{ build_image.tag }}"

    build:
      - prefect_docker.deployments.steps.build_docker_image:
          id: build_image
          requires: "prefect-docker>=0.3.1"
          image_name: "<http://your-account.dkr.ecr.your-region.amazonaws.com/your-repo|your-account.dkr.ecr.your-region.amazonaws.com/your-repo>"
          tag: "2025-08-07-1"
          dockerfile: "./Dockerfile"

    push:
      - prefect_docker.deployments.steps.push_docker_image:
          requires: "prefect-docker>=0.3.1"
          image_name: "{{ build_image.image_name }}"
          tag: "{{ build_image.tag }}"

    # no pull steps needed if WORKDIR is correct

A robust Dockerfile pattern

dockerfile
# Use your private base or Prefect's; just make sure the final image
# actually contains /opt/prefect/home and sets the correct WORKDIR.
FROM prefecthq/prefect:3.1.0-python3.11

# If you must use a private base image, swap the FROM line above:
# FROM {private_repository}

USER root

# Create the directory and ensure permissions
RUN mkdir -p /opt/prefect/home && chown -R prefect:prefect /opt/prefect

# Install dependencies first to leverage Docker layer caching
COPY requirements.txt /opt/prefect/home/requirements.txt
RUN python -m pip install --no-cache-dir -r /opt/prefect/home/requirements.txt

# Copy your code
COPY . /opt/prefect/home

# Set working directory
WORKDIR /opt/prefect/home

# Drop privileges (Prefect images use 'prefect' user)
USER prefect

Other quick checks - Tag discipline: Build with unique tags and reference that exact tag in job_variables.image. latest means “not what you think.” - Multi-stage Dockerfiles: If you use them, ensure the final stage contains /opt/prefect/home. - Absolute paths: Use COPY . /opt/prefect/home (note the leading slash). - If you insist on creating the directory at runtime, add a shell step before set_working_directory to mkdir -p the path—but it’s better to bake it into the image. Docs (so you don’t have to guess) - ECS guide: https://docs-3.prefect.io/integrations/prefect-aws/ecs_guide

So Marvin can do it, he's just being lazy

i might tweak the prompt

@Nate I personally wouldn't mind getting a small survey, I'd feel kinda bad if it didn't help and I had to tell Marvin that. In this case it didn't help 🙃 I'm still facing the same missing directory issue

all feedback is good (especially constructive criticism!) - fwiw in this case marvin’s responses are as good as mine would be, given the information that you shared

@Marvin How exactly would I check the image being used by the flow run? I can check it from both the local and remote (since I pushed to ECR too), but like within the ECS task context I'm not really sure

✅ thought for 145.7 seconds