Scheduled Data Ingestion Workflows with Kubernetes CronJobs

Question

Pulumi · Accepted Answer

To create scheduled data ingestion workflows in Kubernetes, you can leverage CronJobs. A CronJob in Kubernetes is a way to run automated tasks based on a time schedule, similar to crontab in UNIX. A CronJob creates Jobs on a repeating schedule, and Jobs are responsible for running one or more Pods to completion.

Here's what each component is used for:

1. **CronJob**: Defines the schedule and job template. It launches job instances according to a schedule.
2. **Job**: A finite, one-off task that runs one or more Pods. When a specified number of Pods successfully complete, the Job is considered complete.

Consider the following example where a CronJob is set up to run a data ingestion task every hour:

- The `CronJob` resource in Kubernetes will define the schedule (`0 * * * *` which stands for every hour) and the job that should be run. The job template includes a definition of a pod that will perform the actual work.
- The `Job` resource will be created by the CronJob according to this schedule. The job will create a Pod(s) that runs the actual data ingestion script or application.
- Inside the Pod, you can run whatever containerized task you need, such as a Python script, a database dump, or any other data manipulation command.

Let's see how to define this in a Pulumi program using Python:

```python
import pulumi
import pulumi_kubernetes as k8s

# Define the image for the container that will perform the data ingestion.
# Replace 'my-ingestion-image' with the actual image you intend to use.
# This image should contain the code/script that carries out the data ingestion process.
image_name = "my-ingestion-image:latest"

# Define a Kubernetes CronJob.
data_ingestion_cronjob = k8s.batch.v1.CronJob(
    "data-ingestion-cronjob",
    spec=k8s.batch.v1.CronJobSpecArgs(
        # Define the schedule for the cron job.
        # This schedule is in Cron format; this example runs `every hour`.
        schedule="0 * * * *",
        job_template=k8s.batch.v1.JobTemplateSpecArgs(
            spec=k8s.batch.v1.JobSpecArgs(
                template=k8s.core.v1.PodTemplateSpecArgs(
                    spec=k8s.core.v1.PodSpecArgs(
                        containers=[
                            k8s.core.v1.ContainerArgs(
                                name="data-ingestion-container",
                                image=image_name,
                                # Define the command or script within your container that
                                # performs the data ingestion.
                                command=["/path/to/your/script.sh"],
                            )
                        ],
                        # The restart policy for when the job runs.
                        # "Never" means that the job will not restart automatically.
                        restart_policy="Never",
                    ),
                ),
            ),
        ),
    ))

# Export the CronJob name
pulumi.export('cronjob_name', data_ingestion_cronjob.metadata["name"])
```

This Pulumi program does the following:

1. Defines a data ingestion container image, which should contain the necessary code or script for data ingestion.
2. Creates a `CronJob` resource with the specified schedule.
3. Within the `CronJob`, it sets up a `JobTemplate` that creates Pods with the specified container image to carry out the work. The Pods run the script mentioned in the `command` argument.
4. The `restart_policy` is set to `Never`, meaning that once a Pod completes, it will not be restarted.
5. Finally, the program exports the name of the `CronJob`, which can be useful for future references or for integration into other systems.

Ensure that your container image is correctly built with the necessary data ingestion script or application before deploying this `CronJob`.