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<@ULVA73B9P> Can i create a worker using Prefect d...
# ask-marvin
n
@Marvin Can i create a worker using Prefect docker image ? For example, from this image : prefecthq/prefect:3-python3.12, can I use 
prefect worker start --pool "my-docker-pool" --type "docker"
?
m
Yes, you can create a worker using a Prefect Docker image, such as the 
prefecthq/prefect:3-python3.12
, and indeed start a worker with the command 
prefect worker start --pool "my-docker-pool" --type "docker"
. Here's a brief outline on how it works: 1. Create a Work Pool: First, navigate to the Prefect UI, go to the Work Pools tab, and ensure that your pool (e.g., "my-docker-pool") is listed but will initially show as not ready. 2. Start a Worker: On your machine where you have the Prefect Docker image, ensure Prefect is installed. Then, you can run the command to start the worker. This worker will poll the Prefect API to check for scheduled flow runs and execute them. You can dive deeper into this process by checking the Prefect documentation on infrastructure examples using Docker here. It will walk you through the steps of setting up and confirming your worker's status. As for issues related to using Docker workers, there are ongoing discussions and bug reports on GitHub. Some users have reported concerns around concurrency limits and launches not setting worker status correctly. If you run into any specific troubleshooting issues, it may be handy to check out relevant issues raised on the Prefect GitHub repository for possible workarounds. Remember, even with Docker, a worker’s primary role is just like that of Marvin from Hitchhiker's Guide to the Galaxy: performing tasks without much enthusiasm... unless you're into automated workflows! 😏
n
i'd also add 
--install-policy always
because it will need 
prefect-docker
and that flag will install it for you
n
Thank you very much, didn't know about that parameter !
@Marvin I have this error when deploying a flow : "payload": { "intended": { "from": "PENDING", "to": "CRASHED" }, "initial_state": { "type": "PENDING", "name": "Pending" }, "validated_state": { "type": "CRASHED", "name": "Crashed", "message": "Flow run could not be submitted to infrastructure" } }, 
RuntimeError: Could not connect to Docker.
Maybe it has to deal with docker socket ? Here is my dockerswarm yaml file : services: agent: image: prefecthq/prefect:3-python3.12 entrypoint: - "prefect" - "worker" - "start" - "--pool" - "my-docker-pool" - "--type" - "docker" - "--install-policy" - "always" environment: - PREFECT_API_KEY=XXXX - PREFECT_API_URL=XXXX
m
The error you're encountering, "Could not connect to Docker," is usually related to issues with the Docker socket connection. Generally, this happens when the Prefect worker running inside a Docker container doesn't have the necessary permissions or the correct configuration to access the Docker Daemon. Here's what you can do to troubleshoot and potentially fix this problem: 1. Check Docker Socket Permissions: - Ensure that the Docker socket is correctly mounted and available to the Prefect container. You should mount the Docker socket inside your container to allow it to manage Docker processes. - Update your Docker service definition to include a volume that points to the Docker socket, like so:
Copy code
yaml
     services:
       agent:
         image: prefecthq/prefect:3-python3.12
         entrypoint: 
         - "prefect"
         - "worker"
         - "start"
         - "--pool"
         - "my-docker-pool"
         - "--type"
         - "docker"
         - "--install-policy"
         - "always"
         volumes:
           - "/var/run/docker.sock:/var/run/docker.sock"
         environment:
           - PREFECT_API_KEY=XXXX
           - PREFECT_API_URL=<your-prefect-cloud-api-url>
2. Check Docker Daemon is Running: - Make sure that the Docker Daemon is indeed running on the host machine. You can run 
docker ps
to verify. 3. User Permissions: - If you are running the Prefect worker as a non-root user, ensure it has the necessary permissions to access the Docker socket by adding it to the Docker group. You can do this with 
sudo usermod -aG docker <your-user>
. Additionally, based on some GitHub issues, you might need to ensure there's no underlying network or configuration issue affecting Docker connectivity. If these adjustments don't resolve the issue, you can check discussions and examples in the Prefect documentation for additional insights or potential edge cases, such as this Docker example here. By addressing these common socket issues, you should be well on your way to getting that docker-based worker humming along like Marvin on a mission—maybe even with a bit more enthusiasm. 😉
n
@Marvin My flow is deployed correctly on my worker, but on worktime, I have this error that crashes my flow :
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docker.errors.APIError: 500 Server Error for <http+docker://localhost/v1.47/images/create?tag=latest&fromImage=ghcr.io%2Fnathan294%2Fsample_pipeline>: Internal Server Error ("Head "<https://ghcr.io/v2/nathan294/sample_pipeline/manifests/latest>": unauthorized")
m
The error message you're seeing indicates that the Docker process is trying to pull an image from the GitHub Container Registry but is unauthorized. This typically means there is a missing or incorrect authentication setup for accessing private images from the registry. Here are a few suggestions to resolve this issue: 1. Authenticate with the Registry: - If the image you're pulling requires authentication, make sure you've logged into the GitHub Container Registry using Docker. You can do this using Docker CLI with: 
docker login <http://ghcr.io|ghcr.io>
. Enter your GitHub username and a personal access token as the password (remember, your personal access token must have the appropriate scopes to read from the registry). 2. Check Image URL and Tag: - Double-check to ensure the image URL and tag are correct. Mistakes can lead to failed authorization issues. 3. Use Image Pull Secrets: - For authenticated access in container orchestrators like Kubernetes, ensure you're using image pull secrets. This needs to be specified in your deployment's configuration so that the execution environment can access the private repository. 4. Prefect Docker Configuration: - In the Prefect configurations, especially if you're using Prefect deployment scripts, ensure any Docker configurations include the correct credentials or secrets for accessing private images. If you're crafting this within some orchestrated environment like Kubernetes or a similar setup, be sure the node or pod where this is running has access credentials properly set up. For more details and possible configuration examples, you can check the Prefect documentation on Docker image handling: Deploy with Docker. Addressing these settings should help you crank your Prefect flow into action so it won't just sit around feeling unauthorized—unlike Marvin, you'll get your work done efficiently! 🤖
n
@Marvin I don't get where do I need to connect to my registry. Is it my worker ? My flow ? Here is my CI/CD for my (simple) flow : jobs: deploy: name: Deploy runs-on: ubuntu-latest steps: - name: Checkout uses: actions/checkout@v4 - name: Log in to the Container registry uses: docker/login-action@v3 with: registry: ${{ env.REGISTRY }} username: ${{ github.actor }} password: ${{ secrets.CONTAINER_REGISTRY_TOKEN }} - name: Setup Python uses: actions/setup-python@v5 with: python-version: "3.12" - name: Prefect Deploy env: PREFECT_API_KEY: ${{ secrets.PREFECT_API_KEY }} PREFECT_API_URL: ${{ secrets.PREFECT_API_URL }} run: | pip install prefect==3.1.2 prefect-docker==0.6.2 python src/deploy.py
m
In your CI/CD workflow, the authentication to the container registry is done when you log in using the 
docker/login-action
. This step ensures that any Docker commands executed in the subsequent steps within the CI/CD job can access the private containers in the registry. Here's the clarification: 1. CI/CD Pipeline: - The login to the container registry as you've implemented is correct. When you do this step 
Log in to the Container registry
, you're essentially making sure that any subsequent Docker commands in this job (such as a build, push, or pull) have access to your private images. This login is session-based within the context of the GitHub Action job. 2. Worker Node Configuration: - For a flow that runs on a worker node (as part of a distributed system), the worker needs to have the ability to pull the Docker images from the registry. This is done by ensuring the worker environment (or wherever the Prefect worker runs) is also able to authenticate to the registry. - If your worker is set up somewhere besides the CI/CD pipeline (like a VM, Kubernetes, etc.), you need to have the Docker registry credentials configured there as well. This means performing a 
docker login
on your worker environment, similar to your CI/CD, so it can pull images directly when executing Prefect flows. 3. Where to use 
docker/login
: - In CI/CD: You're doing the correct login for purposes like building and pushing images. - On Worker: Make sure the runtime environment for Prefect workers has similar access if they attempt to pull images directly (via a 
docker login
or equivalent mechanism, possibly using Kubernetes Secrets if it's in a Kubernetes cluster). In your setup, make sure both the CI/CD pipeline and the worker environment have proper access to the Docker registry. The login action within the CI/CD ensures your jobs can push or interact with the registry, but ensuring your worker has this access when it tries to pull images during flow runs is equally important.
n
@Marvin how should I modify my worker so it has access to my registry ? Here is my service at the moment : services: agent: image: prefecthq/prefect:3-python3.12 entrypoint: - "prefect" - "worker" - "start" - "--pool" - "my-docker-pool" - "--type" - "docker" - "--install-policy" - "always" volumes: - "/var/run/docker.sock:/var/run/docker.sock" environment: - PREFECT_API_KEY=XXXX - PREFECT_API_URL=<your-prefect-cloud-api-url>
m
To enable your Prefect worker to pull images from a private registry, you'll need to ensure that your Docker environment within the worker has access credentials. Here's how you could modify your Docker service to achieve this: 1. Docker Login Credentials: - First, you need to have your Docker credentials available. You could create a Docker credential configuration file, 
.docker/config.json
, and mount it to your Prefect worker. 2. Modify the Worker Service: - You need to ensure that the service has access to your Docker credentials. Here's how you might adjust your Docker service configuration to include those credentials:
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yaml
services:
  agent:
    image: prefecthq/prefect:3-python3.12
    entrypoint: 
      - "prefect"
      - "worker"
      - "start"
      - "--pool"
      - "my-docker-pool"
      - "--type"
      - "docker"
      - "--install-policy"
      - "always"
    volumes:
      - "/var/run/docker.sock:/var/run/docker.sock"
      - "/path/to/your/docker/config.json:/root/.docker/config.json"  # Make sure this path is correct and accessible
    environment:
      - PREFECT_API_KEY=XXXX
      - PREFECT_API_URL=<your-prefect-cloud-api-url>
3. Step-by-Step: - Create Docker Config: On the machine where you have Docker CLI access, log in to your registry using 
docker login
to create a 
.docker/config.json
file. This file contains the necessary authentication for any Docker commands, like pull, running within the same context. - Mount Config File: Ensure this 
.docker/config.json
is securely mounted into your Prefect worker container (as outlined above). 4. Security Considerations: - Secrets Management: Ensure that the Docker config, especially if it contains access tokens or passwords, is handled securely. Consider using Docker secrets or similar mechanisms if available. - Update Regularly: Ensure that any tokens used have lifetimes appropriate for your security standards and are regenerated if there are any security concerns. By following these steps, your Prefect worker should be able to authenticate with and pull images from your private registry directly during the flow run. If there are additional proxy or network considerations on your infrastructure, adjustments might be necessary.
n
@Marvin I have this error in my yaml file now : invalid mount config for type "bind": bind source path does not exist: /root/.docker/config.json Isn't there any other choice to allow my Worker to connect to my registry ?
m
If the bind source path for the Docker config does not exist, it means that the file path specified doesn't match where your 
.docker/config.json
is located. Here are some alternative approaches to allow your Prefect worker to access the registry: 1. Correct the Bind Path: - Ensure the 
.docker/config.json
file exists on your host machine at the expected path. If it's different, adjust the bind mount path accordingly. - Find the actual path using 
echo $HOME
to ensure you're pointing to the correct user's 
.docker
directory. 2. Docker Environment Variables: - Set environment variables on the worker to pass Docker login credentials directly. This method is slightly less secure if not handled properly (avoid logging or exposing inappropriately). - Use the following environment variables in your worker definition:
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yaml
     environment:
       - DOCKER_USERNAME=your-username
       - DOCKER_PASSWORD=your-password  # or use a more secure method below
3. Using Docker Secrets: - If your environment supports Docker secrets, this is a much safer way to handle sensitive information: - Create a Docker secret from your config file: 
docker secret create my_docker_config /path/to/docker/config.json
- Update your service to use this secret. 4. Configure Registry Credentials in Prefect: - Prefect can manage some credentials. You might check if you can utilize Prefect blocks for credential management to store and access your registry credentials securely. 5. Image Pull Secrets in Orchestrated Environments: - If this worker runs in environments like Kubernetes, set up an image pull secret. Ensure Kubernetes has your credentials and configure Prefect to reference them. If environment variables or setting up Docker secrets isn't feasible in your deployment scenario, make sure the file path you're using to mount the Docker config file is correct. Additionally, check access permissions to ensure the Prefect worker can read this configuration.
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