Running a Python Script

This tutorial serves as an introduction to Bacalhau. In this example, you'll be executing a simple "Hello, World!" Python script hosted on a website on Bacalhau.

Prerequisites​

To get started, you need to install the Bacalhau client, see more information here

1. Running Python Locally​

We'll be using a very simple Python script that displays the traditional first greeting. Create a file called hello-world.py:

# hello-world.py
print("Hello, world!")

Running the script to print out the output:

python3 hello-world.py

After the script has run successfully locally we can now run it on Bacalhau.

2. Running a Bacalhau Job​

To submit a workload to Bacalhau you can use the bacalhau docker run command. This command allows passing input data into the container using content identifier (CID) volumes, we will be using the --input URL:path argument for simplicity. This results in Bacalhau mounting a data volume inside the container. By default, Bacalhau mounts the input volume at the path /inputs inside the container.

Bacalhau overwrites the default entrypoint, so we must run the full command after the -- argument.

export JOB_ID=$(bacalhau docker run \
    --id-only \
    --input https://raw.githubusercontent.com/bacalhau-project/examples/151eebe895151edd83468e3d8b546612bf96cd05/workload-onboarding/trivial-python/hello-world.py \
    python:3.10-slim \
    -- python3 /inputs/hello-world.py)

Structure of the command​

1. bacalhau docker run: call to Bacalhau

2. --id-only: specifies that only the job identifier (job_id) will be returned after executing the container, not the entire output

3. --input https://raw.githubusercontent.com/bacalhau-project/examples/151eebe895151edd83468e3d8b546612bf96cd05/workload-onboarding/trivial-python/hello-world.py \: indicates where to get the input data for the container. In this case, the input data is downloaded from the specified URL, which represents the Python script "hello-world.py".

4. python:3.10-slim: the Docker image that will be used to run the container. In this case, it uses the Python 3.10 image with a minimal set of components (slim).

5. --: This double dash is used to separate the Bacalhau command options from the command that will be executed inside the Docker container.

6. python3 /inputs/hello-world.py: running the hello-world.py Python script stored in /inputs.

When a job is submitted, Bacalhau prints out the related job_id. We store that in an environment variable so that we can reuse it later on.

Declarative job description​

The same job can be presented in the declarative format. In this case, the description will look like this:

name: Running Trivial Python
type: batch
count: 1
tasks:
  - name: My main task
    Engine:
      type: docker
      params:
        Image: python:3.10-slim
        Entrypoint:
          - /bin/bash
        Parameters:
          - -c
          - python3 /inputs/hello-world.py
    InputSources:
      - Target: /inputs
        Source:
          Type: urlDownload
          Params:
            URL: https://raw.githubusercontent.com/bacalhau-project/examples/151eebe895151edd83468e3d8b546612bf96cd05/workload-onboarding/trivial-python/hello-world.py
            Path: /inputs/hello-world.py

The job description should be saved in .yaml format, e.g. helloworld.yaml, and then run with the command:

bacalhau job run helloworld.yaml

3. Checking the State of your Jobs​

Job status: You can check the status of the job using bacalhau list.

bacalhau list --id-filter ${JOB_ID} --no-style

When it says Published or Completed, that means the job is done, and we can get the results.

Job information: You can find out more information about your job by using bacalhau describe.

bacalhau describe ${JOB_ID}

Job download: You can download your job results directly by using bacalhau get. Alternatively, you can choose to create a directory to store your results. In the command below, we created a directory (results) and downloaded our job output to be stored in that directory.

rm -rf results && mkdir results
bacalhau get ${JOB_ID} --output-dir results

4. Viewing your Job Output​

To view the file, run the following command:

cat results/stdout

Support​

If you have questions or need support or guidance, please reach out to the Bacalhau team via Slack (#general channel).