@Marvin: Please give an answer for prefect 3. How can I have a docker worker mount a local folder into the flow container? E.g. on the docker host I have /tmp/large-files and want to have it in the flow container as /mnt/large-files Please specifiy either using prefect worker start [...] (preferred solution) or using docker compose to start a prefect worker

To mount a local folder into a flow container using a Prefect worker, you can either use the

prefect worker start

command or configure it through Docker Compose. Here's how you can achieve both: ### Using

prefect worker start

1. Start the worker: You can use the

prefect worker start

command to start a worker. You need to specify the work pool name and use the

--volume

option to mount a local directory. Unfortunately, the direct syntax for volume mounting isn't explicitly documented, but you can typically use Docker's volume syntax. Example command:

bash
   prefect worker start --pool my-docker-pool --volume /tmp/large-files:/mnt/large-files

### Using Docker Compose 1. Docker Compose Configuration: You can define the volume in your

docker-compose.yaml

file. Here's an example configuration:

yaml
   services:
     worker:
       image: prefecthq/prefect:2-python3.12
       restart: always
       command:
         [
           "prefect",
           "worker",
           "start",
           "--pool",
           "docker-work",
           "--install-policy",
           "if-not-present"
         ]
       volumes:
         - /tmp/large-files:/mnt/large-files
       environment:
         - DOCKER_HOST=unix:///var/run/docker.sock

For more detailed information on Prefect workers and Docker configurations, you might find these links useful: - Prefect Infrastructure Concepts - Docker Infrastructure Examples If you have any further questions or need additional details, feel free to ask.

@Marvin: Would I be able to specifc this in the prefect.yaml? If so, how?

The

prefect.yaml

file is primarily used for defining deployment configurations, and it allows for some templating and dynamic value referencing. However, it doesn't natively support specifying Docker volume mounts directly within the file. For Docker-specific configurations like volume mounts, you typically need to define these in Docker-related files such as

docker-compose.yaml

or within the Docker command itself. The

prefect.yaml

is more about orchestrating Prefect-specific settings and referencing dynamic values or environment variables. If you are using Prefect's deployment capabilities, you might need to handle Docker volume configurations separately in your Docker setup or use environment variables to manage paths dynamically. For more details on what you can configure in

prefect.yaml

, you can refer to the Prefect YAML documentation. If you have further questions or need more details on configuring Prefect deployments, feel free to ask.

@Marvin: How does the prefect 3 docker worker actually start the container? How can I have the worker mount a local folder to this container?

In Prefect 3.x, the Docker worker starts a container by polling the Prefect API for scheduled flow runs and then executing them on Docker infrastructure. The worker itself acts as a lightweight process that continuously checks for tasks to execute. To mount a local folder to the container started by a Prefect Docker worker, you can specify volume mounts using Docker's volume syntax. Here's how you can do it: 1. Via CLI: When starting a worker using the

prefect worker start

command, you can pass Docker-specific options to mount volumes. However, the exact command-line options for volume mounts aren't directly documented in Prefect's CLI. You might need to handle this through Docker directly or within a Docker Compose setup. 2. Via Docker Compose: You can define volumes in a

docker-compose.yaml

file, which will be respected when the worker starts the container. Here’s an example configuration:

yaml
   services:
     worker:
       image: prefecthq/prefect:2-python3.12
       restart: always
       command:
         [
           "prefect",
           "worker",
           "start",
           "--pool",
           "docker-work",
           "--install-policy",
           "if-not-present"
         ]
       volumes:
         - /tmp/large-files:/mnt/large-files
       environment:
         - DOCKER_HOST=unix:///var/run/docker.sock

For more details on Docker infrastructure and worker configurations, you can refer to the Prefect Infrastructure Examples. If you have further questions or require more specific details, feel free to ask.

@Marvin: 1. Please make the docker compose example use prefect 3 2. How is the volume mount of the worker affecting the flow containers?

### Updated Docker Compose Example for Prefect 3 To use Prefect 3 with Docker Compose, you can set up your

docker-compose.yaml

like this:

yaml
services:
  worker:
    image: prefecthq/prefect:3.0.0rc2-python3.12
    restart: always
    command:
      [
        "prefect",
        "worker",
        "start",
        "--pool",
        "docker-work",
        "--install-policy",
        "if-not-present"
      ]
    volumes:
      - /tmp/large-files:/mnt/large-files
    environment:
      - PREFECT_API_URL=<http://localhost:4200/api>
      - DOCKER_HOST=unix:///var/run/docker.sock

### Volume Mount Effect on Flow Containers The volume mounts specified for the worker in Docker do not automatically propagate to the containers that run the flows. Each flow run is executed in its own container, and the configuration for that container is determined by the infrastructure settings of the work pool or specific deployment configurations. If you need the flow container to have access to a host directory, you would need to specify this in the deployment's infrastructure settings, typically using a Docker infrastructure block or similar configuration where you can define volume mounts explicitly for the flow containers. For more detailed guidance on setting up Docker infrastructure for Prefect 3, you can refer to the Prefect Docker Infrastructure Examples. If you have further questions or need additional help, feel free to ask.

hi @Bernhard - i think the thing marvin is not telling you here is that volumes go on your docker work pool