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Create a self-deleting virtual machine on Compute Engine

Author(s): @engelke @lauriewhite ,   Published: 2019-05-15

Google Cloud Community tutorials submitted from the community do not represent official Google Cloud product documentation.


Learning to use Google Cloud Platform (GCP) is best done hands-on, by actually creating, using, and removing resources. However, a common problem with doing this is that learners may forget to clean up their resources when finished trying something, resulting in continuing running resources, often at a cost.

This tutorial shows how to create Compute Engine instances (virtual machines) that will automatically delete themselves after a set time, ensuring that those resources will not remain and incur charges indefinitely, even if the learner forgets to clean them up. A variation is also shown that will simply stop the instances after a set time, after which they can be restarted—and again automatically stop after the set time. Be aware that stopped instances, unlike deleted instances, still incur some charges (see Compute Engine pricing for details).

The use of self-deleting virtual machines is particularly useful in class settings.

Objectives

Learn how to create Compute Engine instances that will delete themselves after a set period of time. You will see two ways to do this:

  • Using the GCP Console
  • Using the gcloud command-line tool

Before you begin

Create a GCP project in a web browser:

  1. Open your web browser to the GCP Console.
  2. Sign in with a Google or G Suite account. If you don't have an account, you can create one by clicking Create account.
  3. Click Select a project at the top of the page, and then click New Project.
  4. Enter a name for your project, and note the project ID shown under the Project name field.
  5. Select a location.
  6. Click Create.

    A notification appears, saying that the project is being created.

  7. When the notification says that the project is ready, click the notification or select the project from the project selector menu to open the project.

Use this new project in the tutorial below so that you don't inadvertently affect your other projects, if you have any.

Costs

In this tutorial, you create a Compute Engine instance. That instance incurs charges as long as it exists, as listed in the Compute Engine pricing. Your account can use one micro instance (the kind created in this tutorial) as part of the Free Tier, which incurs no costs.

Creating the startup script

The self-deleting instance works by automatically executing a startup script that waits a set amount of time and then issues a gcloud command to delete itself. This script needs to be provided in a file or at an available URL when launching the instance.

  1. Open a text editor and enter the following text:

    #!/bin/sh
    sleep 3600s
    export NAME=$(curl -X GET http://metadata.google.internal/computeMetadata/v1/instance/name -H 'Metadata-Flavor: Google')
    export ZONE=$(curl -X GET http://metadata.google.internal/computeMetadata/v1/instance/zone -H 'Metadata-Flavor: Google')
    gcloud --quiet compute instances delete $NAME --zone=$ZONE
    
  2. Save the file as startup.sh.

When you start a new instance and specify that it should automatically run this script, it will do nothing for one hour (the 3600s value on the second line), then look up information about the running instance and put it in shell variables (the third and fourth lines), and finally run a gcloud command to delete itself.

You can use this file as is to make your instances delete themselves after one hour (3600 seconds), or you can customize it to your exact needs:

  • You can modify the script to stop the instance rather than deleting it. To make this change, replace delete in the gcloud command with stop.

  • You can change the duration before self-deletion by replacing 3600s with a different value. A number, or a number followed by an s, stands for that number of seconds. You can specify a duration in minutes, hours, or days, by using the suffix m, h, or d in place of s.

  • Instead of the instance deleting itself after a given duration, you can have the instance install and configure a program to run, and then delete itself when that program completes. Replace the sleep 3600s line with one or more commands to install, configure, and run the program you want.

Every standard Linux option in Compute Engine includes the gcloud command-line tool.

How the startup script works

This section explains how the file created in the previous section works. You can skip this section if you just want to create self-deleting instances.

Every Linux OS image available by default in Compute Engine is configured to run a program when the operating system starts, if you specify such a program. The startup.sh file created in the previous section is such a program.

The startup script that you created in the previous section does nothing but wait for an hour and then issue a command to delete the instance that runs the script.

Let's look at an explanation of what each line in startup.sh does:

Invoking the Bourne shell

#!/bin/sh

If the first two characters in the file are #!, as they are here, the Linux environment will run the program named, providing the file as its input. So, Linux will invoke /bin/sh, the Bourne shell, to run this file. You may be familiar with Bash in the terminal window for Linux and Mac machines. The Bourne shell is an earlier, similar program for running commands.

Waiting for an hour

sleep 3600s

This line runs the sleep program, which does nothing but wait the specified time before it exits, which introduces a delay of an hour (3600 seconds) before the next commands are run.

Setting shell variables to specify the instance

export NAME=$(curl -X GET http://metadata.google.internal/computeMetadata/v1/instance/name -H 'Metadata-Flavor: Google')
export ZONE=$(curl -X GET http://metadata.google.internal/computeMetadata/v1/instance/zone -H 'Metadata-Flavor: Google')

Each of these lines sets the value of a shell variable (NAME and ZONE). These variables are used in a later command. The $(command) portion runs the command in the parentheses and returns the output of that command as its value. The commands here are each curl commands that make web requests and output the responses to the requests.

Compute Engine instances have access to a metadata service that looks like a web site. Any web request made to that apparent site (http://metadata.google.internal) will fetch some information about the instance itself. There is no actual network traffic involved, though; the GCP infrastructure handles the requests and responses internally. That's one of the reasons that it is safe for the URL to start with http instead of https: because there is no actual network activity, there is no need for a secure network connection.

These two metadata requests discover the running instance's name and zone, which are required for the last line of the program.

Deleting the instance

gcloud --quiet compute instances delete $NAME --zone=$ZONE

This last line runs the gcloud command. The --quiet option indicates that the command should not ask for user confirmation of an action, because it runs in batch mode with no user available. The compute instances command group performs operations on Compute Engine instances. The delete command completely removes an instance. The instance NAME and ZONE variables in the command specify which instance to delete. You can replace delete with stop to stop the instance so that it can be restarted later.

Using the console to create a self-deleting instance

This section gives the steps to create a self-deleting instance by using the GCP Console in your web browser. If you prefer to use the command line instead, see the next section.

  1. Open the GCP Console and select your project, if it is not already selected.

  2. Click the Navigation menu in the upper-left corner of the console, and then select Compute Engine > VM instances.

  3. On the VM instances page, click Create.

  4. In the New VM instance form, leave most values at the default values, but change the following values:

    • Name: Fill in any name (for example, myinstance).
    • Region and Zone: Select a location near you.
    • Access Scopes (in the Identity and API access section): Select Set access for each API, and then choose Read Write from the Compute Engine menu in this section.
  5. Click Management, security, disks, networking, sole tenancy at the bottom of the form to open more sections of the form.

  6. Copy the statup script from the "Preparation" section in this tutorial, and paste the script into the Startup script field in the Automation section of the form.

    For testing purposes you may want to change the sleep duration from 3600s to only 300s.

  7. Click Create.

In the list of your VM instances, a spinning icon next to your new instance indicates that it is starting. When the instance is ready, the spinner changes to a green icon with a check mark.

Wait the duration that you specified in the script. The instance that you created should disappear from the list. The list is automatically updated periodically; you can click the Refresh button to update the list at any time.

Using the command line to create a self-deleting instance

This section gives the steps to create a self-deleting instance by using the command line on your local computer. If you prefer to use the web console instead, see the previous section, "Using the console".

  1. Install the Cloud SDK.

  2. Log in to your GCP account:

    gcloud auth login
    
  3. Select the project you want to work in:

    gcloud init
    
  4. Create a self-deleting virtual machine:

    gcloud compute instances create myinstance \
    --metadata-from-file=startup-script=startup.sh \
    --scopes=compute-rw
    

    Replace myinstance in this command with your instance name.

    This command uses the startup.sh file that you created in the "Preparation" section early in this tutorial.

    For an explanation of the other options in this command, see the "Options" section below.

  5. You may be prompted to allow the SDK to create the needed API if you haven't used it before. Go ahead and answer Y for yes if needed.

  6. You will be asked to select a region for your instance to run in. Select one in a location that is convenient for you and your users.

In a few minutes, you should see a confirmation that the instance has been created successfully:

Created [https://www.googleapis.com/compute/v1/projects/myproject/zones/us-central1-a/instances/myinstance].
NAME        ZONE           MACHINE_TYPE   PREEMPTIBLE  INTERNAL_IP  EXTERNAL_IP     STATUS
myinstance  us-central1-a  n1-standard-1               10.128.0.2   35.239.136.206  RUNNING

You can check on your running instances at any time with this command:

gcloud compute instances list

Wait until the specified sleep time has expired, and run that command again. The instance should be gone.

Options

The --metadata-from-file=startup-script=startup.sh option specifies that the new instance's metadata-server should provide the contents of the startup.sh file as the value of startup-script when the instance requests it. For standard Compute Engine instances, that will cause the instance to run that script when it starts.

The --scopes=compute-rw option specifies that the instance should have permission to use all Compute Engine APIs, including the API to delete an instance. By default, new instances do not have that privilege, so it needs to be added here so it can delete itself.

Cleaning up

If everything went as planned, the only resource you created, the new instance, cleaned itself up. If you no longer need the project you created for trying this out, you can delete it, too, eliminating every resource in it.

  1. Click the Navigation menu in the upper-left corner of the console, and then select Home.

  2. In the Project info box, click Go to project settings.

  3. Click Shut down.

  4. To confirm project deletion, enter the project ID.

  5. Click Shut down below the project ID you entered. The project will be shut down and will be deleted in 30 days.

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