This sample retrieves the hostname of a given Compute Engine instance.

## 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.md.txt).

```go
import (
	"context"
	"fmt"
	"io"

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

// getInstanceHostname prints the hostname of the Google Cloud VM instance.
func getInstanceHostname(w io.Writer, projectID, zone, instanceName string) error {
	// projectID := "your_project_id"
	// zone := "europe-central2-b"
	// instanceName := "your_instance_name"

	ctx := context.Background()
	instancesClient, err := compute.NewInstancesRESTClient(ctx)
	if err != nil {
		return fmt.Errorf("NewInstancesRESTClient: %w", err)
	}
	defer instancesClient.Close()

	req := &computepb.GetInstanceRequest{
		Project:  projectID,
		Zone:     zone,
		Instance: instanceName,
	}

	instance, err := instancesClient.Get(ctx, req)
	if err != nil {
		return fmt.Errorf("unable to get instance: %w", err)
	}

	// If a custom hostname is not set, the output for instance.GetHostname() will be ""
	fmt.Fprintf(w, "Instance %v has hostname: %v", instanceName, instance.GetHostname())

	return nil
}
```

### Java


Before trying this sample, follow the Java 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 Java API
reference documentation](https://docs.cloud.google.com/java/docs/reference/google-cloud-compute/latest/overview).


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.md.txt).

```java

import com.google.cloud.compute.v1.Instance;
import com.google.cloud.compute.v1.InstancesClient;
import java.io.IOException;

public class GetInstanceHostname {

  public static void main(String[] args) throws IOException {
    // TODO(developer): Replace these variables before running the sample.
    String project = "your-project-id";
    String zone = "zone-name"; // eg: "us-central1-a"
    String instanceName = "instance-name"; // Name of the VM instance to retrieve.

    getInstanceHostname(project, zone, instanceName);
  }

  // Retrieves the hostname of the Google Cloud VM instance.
  public static void getInstanceHostname(String projectId, String zone, String instanceName)
      throws IOException {
    try (InstancesClient instancesClient = InstancesClient.create()) {

      Instance instance = instancesClient.get(projectId, zone, instanceName);

      if (instance.hasHostname()) {
        // If a custom hostname is not set, the output for instance.getHostname() will be undefined.
        System.out.printf("Custom Hostname for the instance %s is: %s", instanceName,
            instance.getHostname());
      }
    }
  }

}
```

### Node.js


Before trying this sample, follow the Node.js 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 Node.js API
reference documentation](https://docs.cloud.google.com/nodejs/docs/reference/compute/latest).


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.md.txt).

```javascript
/**
 * TODO(developer): Uncomment and replace these variables before running the sample.
 */
// const projectId = 'YOUR_PROJECT_ID';
// const zone = 'europe-central2-b'
// const instanceName = 'YOUR_INSTANCE_NAME'

const compute = require('@google-cloud/compute');

async function getInstanceHostname() {
  const instancesClient = new compute.InstancesClient();

  const [instance] = await instancesClient.get({
    project: projectId,
    zone,
    instance: instanceName,
  });
  // If a custom hostname is not set, the output for instance.hostname will be undefined
  console.log(`Instance ${instanceName} has hostname: ${instance.hostname}`);
}

getInstanceHostname();
```

### Python


Before trying this sample, follow the Python 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 Python API
reference documentation](https://docs.cloud.google.com/python/docs/reference/compute/latest).


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.md.txt).

```python
from google.cloud import compute_v1


def get_hostname(project_id: str, zone: str, instance_name: str) -> str:
    """
    Retrieve the hostname of given instance.

    Args:
        project_id: project ID or project number of the Cloud project you want to use.
        zone: name of the zone you want to use. For example: "us-west3-b"
        instance_name: name of the virtual machine to check.

    Returns:
        The hostname of an instance.
    """
    instance_client = compute_v1.InstancesClient()
    instance = instance_client.get(
        project=project_id, zone=zone, instance=instance_name
    )
    return instance.hostname

```

## 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.md.txt?product=computeengine).