Using kubernetes cronjobber.hidde.co with jetstream.nats.io

Question

Pulumi · Accepted Answer

To create a Kubernetes CronJob that interacts with a NATS JetStream instance, you'll need to define a `CronJob` resource in Pulumi that uses a container image capable of communicating with NATS JetStream. The container could, for example, be a custom image with the NATS CLI installed or any other tool that allows you to interact with NATS JetStream.

Below, I'll guide you through writing a Pulumi TypeScript program to create a Kubernetes CronJob that can be used for scheduling tasks to interact with a NATS JetStream server.

First, you'll need a Docker image that contains the necessary tools to communicate with NATS. This could be an image that contains the `nats` CLI tool. For simplicity, I'll assume such an image is available with the name `nats-jetstream-client:latest`.

This program will create a `CronJob` resource in Kubernetes using the `@pulumi/kubernetes` package. The `CronJob` will be configured to run on a schedule and use the `nats-jetstream-client` container.

Before you begin, make sure you have Pulumi and Kubernetes set up. You can refer to the [Pulumi documentation](https://www.pulumi.com/docs/get-started/) for getting started with Pulumi and the [Kubernetes documentation](https://kubernetes.io/docs/tasks/) for Kubernetes tasks.

Here's the basic Pulumi program that sets up a CronJob:

```typescript
import * as k8s from "@pulumi/kubernetes";

// Define the cron job schedule and job details
const cronJob = new k8s.batch.v1.CronJob("nats-cron-job", {
    metadata: {
        // Namespace where the cron job will be placed
        namespace: "default",
    },
    spec: {
        schedule: "*/5 * * * *", // Run every 5 minutes
        jobTemplate: {
            spec: {
                template: {
                    spec: {
                        containers: [{
                            name: "nats-jetstream-client",
                            image: "nats-jetstream-client:latest",
                            // Command to be executed at each scheduled interval
                            command: ["/bin/sh", "-c"],
                            args: [
                                // Replace the following with the actual NATS JetStream interaction command you need
                                "nats pub subjectName 'Hello from Pulumi scheduled job!'"
                            ],
                        }],
                        restartPolicy: "OnFailure", // Restart the job on failure
                    },
                },
            },
        },
    },
});

// Export the name of the cron job
export const cronJobName = cronJob.metadata.name;
```

Let's step through this program:

- We import the `@pulumi/kubernetes` package to interact with Kubernetes resources using Pulumi.
- A new CronJob resource is created with a schedule (`spec.schedule`) to run every 5 minutes.
- The `jobTemplate.spec.template.spec` defines the Pod spec for the job the CronJob will run on each schedule trigger.
- The container specification includes the name of the container (`nats-jetstream-client`), the image to use (`nats-jetstream-client:latest`), and the command to execute, which is a placeholder for your actual NATS JetStream publish command.
- The `restartPolicy` is set to `"OnFailure"` to ensure that the job is restarted if it fails.
- Lastly, we export the name of the CronJob to be accessible outside the program if needed.

Remember to replace the `args` in the container spec with the actual command you intend to use to interact with NATS JetStream.

This program is usable as it stands, but you will need to customize the `image` and `args` for the container to match your specific use-case for interacting with NATS JetStream.

To apply this Pulumi program, save the code in a file (e.g., `index.ts`), and run `pulumi up`. Ensure you're in the right directory and have selected the correct Kubernetes cluster context with Pulumi. After confirming the plan, the CronJob resource will be created in your Kubernetes cluster.