Attach a regional disk to a Compute Engine VM instance in read-write mode

Attach a regional disk to a single virtual machine running in Google Compute Engine. The disk also needs to be mounted by the operating system before it can be used.

The disk is attached in read-only mode. The disk can be attached to multiple VM instances simultaneously.

## Code sample

### Go


Before trying this sample, follow the Go setup instructions in the
[Compute Engine quickstart using
client libraries](https://docs.cloud.google.com/compute/docs/api/using-libraries).


For more information, see the
[Compute Engine Go API
reference documentation](https://docs.cloud.google.com/go/docs/reference/cloud.google.com/go/compute/latest/apiv1).


To authenticate to Compute Engine, set up Application Default Credentials.
For more information, see

[Set up authentication for a local development environment](https://docs.cloud.google.com/docs/authentication/set-up-adc-local-dev-environment).

    import (
    	"context"
    	"fmt"
    	"io"

    	compute "cloud.google.com/go/compute/apiv1"
    	computepb "cloud.google.com/go/compute/apiv1/computepb"
    )

    // Attaches the provided regional disk in read-only mode to the given VM.
    // Read-only disks can be attached to multiple VMs at once.
    func attachRegionalDiskReadOnly(w io.Writer, projectID, zone, instanceName, diskUrl string) error {
    	// projectID := "your_project_id"
    	// zone := "us-west3-a" // refers to the instance, not the disk
    	// instanceName := "your_instance_name"
    	// diskUrl := "projects/your_project/regions/europe-west3/disks/your_disk"

    	ctx := context.Background()
    	instancesClient, err := compute.https://docs.cloud.google.com/go/docs/reference/cloud.google.com/go/compute/latest/apiv1.html#cloud_google_com_go_compute_apiv1_InstancesClient_NewInstancesRESTClient(ctx)
    	if err != nil {
    		return err
    	}
    	defer instancesClient.Close()

    	mode := "READ_ONLY"

    	req := &computepb.AttachDiskInstanceRequest{
    		AttachedDiskResource: &computepb.AttachedDisk{
    			Source: &diskUrl,
    			Mode:   &mode,
    		},
    		Instance: instanceName,
    		Project:  projectID,
    		Zone:     zone,
    	}

    	op, err := instancesClient.AttachDisk(ctx, req)
    	if err != nil {
    		return fmt.Errorf("unable to attach disk: %w", err)
    	}

    	if err = op.Wait(ctx); err != nil {
    		return fmt.Errorf("unable to wait for the operation: %w", err)
    	}

    	fmt.Fprintf(w, "Disk attached\n")

    	return nil
    }

## What's next


To search and filter code samples for other Google Cloud products, see the
[Google Cloud sample browser](https://docs.cloud.google.com/docs/samples?product=computeengine).