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Startup scripts

We can run our own startup scripts from VM instances to perform automatic actions such as updating the system, and sending notifications and so on.

A startup script is specified using metadata keys through the metadata server and can be applied using the console or gcloud command line:

Once you have set the default region and zone for your instance, you can provide a startup script using the gcloud command line while creating an instance. The script is provided with a—metadata flag:

    gcloud compute instances create example-instance --tags http-server 
    --metadata startup-script='#! /bin/bash
    # Installs apache and a custom homepage
    # Go to root directory
    sudo su -
    # For automatic Updates
    apt-get update
    # Install apache
    apt-get install -y apache2
    # Edit index.html file
    cat <<EOF > /var/www/html/index.html
    <html><body><h1>Hello World</h1>
    <p>This page was created from a simple start up script!</p>
    </body></html>
    EOF'

For an already running instance, startup scripts can be added using the add-metadata flag as follows. The path can be a URL as well, which means that the script can also be located from a Cloud Storage bucket object:

gcloud compute instances add-metadata example-instance  --metadata-from-file startup-script=path/to/file