Startup scripts for automation in GCP - Step-by-Step Execution

Process Flow - Startup scripts for automation

Instance boots up

↓

Startup script triggered

↓

Script runs commands

↓

Commands configure instance

↓

Instance ready with automation applied

When a cloud instance starts, it runs a startup script automatically to set up or configure itself before becoming ready.

Execution Sample

GCP

#!/bin/bash
apt-get update
apt-get install -y nginx
systemctl start nginx

This startup script updates packages, installs nginx web server, and starts the nginx service automatically on instance boot.

Process Table

Step	Action	Command	Result	Instance State
1	Instance boots	N/A	Instance starts running	Booting
2	Startup script triggered	Run script	Script begins execution	Running script
3	Update packages	apt-get update	Package list refreshed	Updating packages
4	Install nginx	apt-get install -y nginx	Nginx installed	Installing software
5	Start nginx service	systemctl start nginx	Nginx service started	Configured and running
6	Script ends	N/A	Startup script finished	Ready

💡 Startup script completes all commands; instance is configured and ready.

Status Tracker

Variable	Start	After Step 3	After Step 4	After Step 5	Final
Instance State	Booting	Updating packages	Installing software	Configured and running	Ready

Key Moments - 3 Insights

Why does the startup script run automatically without manual intervention?

Because the cloud instance is configured to execute the startup script at boot time, as shown in execution_table step 2.

What happens if a command in the startup script fails?

The script may stop or continue depending on error handling, but the instance might not be fully configured; this is why monitoring script success is important.

Can the startup script install software that requires internet access?

Yes, but the instance must have network access during startup, as seen in step 3 where package lists are updated from online sources.

Visual Quiz - 3 Questions

Look at the execution_table, what is the instance state after the nginx installation command?

A Configured and running

B Booting

C Installing software

D Ready

💡 Hint

Check the 'Instance State' column at step 4 in the execution_table.

At which step does the startup script begin execution?

A Step 1

B Step 2

C Step 3

D Step 6

💡 Hint

Refer to the 'Action' column in the execution_table to find when the script starts.

If the command 'systemctl start nginx' failed, what would likely be the instance state?

A Not fully configured

B Booting

C Installing software

D Updating packages

💡 Hint

Consider the final instance state after step 5 in the execution_table and what failure would imply.

Concept Snapshot

Startup scripts run automatically when a cloud instance boots.
They execute commands to configure the instance.
Common uses: install software, start services.
Scripts run before instance is ready.
Ensure scripts have correct commands and permissions.

Full Transcript

When a cloud instance starts, it automatically runs a startup script. This script contains commands like updating packages, installing software such as nginx, and starting services. The execution flow begins with the instance booting, then triggering the script, running each command step-by-step, and finally the instance becomes ready with the automation applied. Variables like instance state change from booting to ready as the script progresses. Key points include understanding that the script runs without manual input, network access is needed for package installation, and failure in commands can leave the instance partially configured. The visual quiz tests understanding of the instance state at different steps and the script execution timing.

Practice

1. What is the main purpose of a startup script in a Google Cloud VM instance?

easy

A. To automate tasks when the VM boots

B. To manually start the VM

C. To create a new VM instance

D. To delete files from the VM

Solution

1. Step 1: Understand startup script role

   Startup scripts run automatically when a VM starts to perform tasks without manual intervention.

2. Step 2: Identify correct purpose

   Among the options, only automating tasks at boot matches the startup script function.

3. Final Answer:

   To automate tasks when the VM boots -> Option A

4. Quick Check:

   Startup script = automate tasks at boot [OK]

Hint: Startup scripts run automatically at VM boot time [OK]

Common Mistakes:

• Confusing startup scripts with manual commands
• Thinking startup scripts create or delete VMs
• Assuming startup scripts run after user login

2. Which command correctly adds a startup script to a new VM instance using gcloud CLI?

easy

A. gcloud compute instances create my-vm --metadata startup='echo Hello'

B. gcloud compute instances create my-vm --script-startup='echo Hello'

C. gcloud compute instances create my-vm --startup='echo Hello'

D. gcloud compute instances create my-vm --metadata startup-script='echo Hello'

Solution

1. Step 1: Recall correct flag for startup script

   The correct metadata key to add a startup script is 'startup-script'.

2. Step 2: Match command syntax

   gcloud compute instances create my-vm --metadata startup-script='echo Hello' uses '--metadata startup-script' correctly; others use invalid flags.

3. Final Answer:

   gcloud compute instances create my-vm --metadata startup-script='echo Hello' -> Option D

4. Quick Check:

   Use --metadata startup-script to add scripts [OK]

Hint: Use --metadata startup-script flag with gcloud create [OK]

Common Mistakes:

• Using incorrect flag names like --script-startup
• Confusing metadata keys with other flags
• Missing quotes around the script content

3. Given this startup script added to a VM:

#!/bin/bash
echo "Hello World" > /var/log/startup.log

What will happen when the VM boots?

medium

A. The VM will fail to boot due to script error

B. The file /var/log/startup.log will contain 'Hello World'

C. Nothing happens because echo is not allowed

D. The file /var/log/startup.log will be deleted

Solution

1. Step 1: Analyze the script commands

   The script writes the text 'Hello World' into the file /var/log/startup.log using echo and redirection.

2. Step 2: Understand script effect on boot

   Since startup scripts run as root, the file will be created or overwritten with the text.

3. Final Answer:

   The file /var/log/startup.log will contain 'Hello World' -> Option B

4. Quick Check:

   Startup script writes text to log file [OK]

Hint: Startup scripts run as root and can write files [OK]

Common Mistakes:

• Assuming echo command is blocked
• Thinking the file will be deleted instead of created
• Believing the VM will fail due to simple echo

4. You wrote this startup script:

#!/bin/bash
apt-get update
apt-get install nginx -y

But nginx is not installed after VM boots. What is the likely problem?

medium

A. The script lacks 'sudo' before commands

B. The script is missing the shebang line

C. The script runs before network is ready

D. The script should use 'yum' instead of 'apt-get'

Solution

1. Step 1: Check script commands and environment

   The script uses apt-get which requires network access to update and install packages.

2. Step 2: Identify timing issue

   Startup scripts may run before network is fully ready, causing apt-get to fail silently.

3. Final Answer:

   The script runs before network is ready -> Option C

4. Quick Check:

   Network must be ready before package install [OK]

Hint: Ensure network is ready before package installs in startup scripts [OK]

Common Mistakes:

• Adding sudo unnecessarily (scripts run as root)
• Ignoring network readiness in startup timing
• Using wrong package manager for Debian-based VM

5. You want to automate VM setup to install Apache, create a website folder, and start the service on boot. Which startup script snippet correctly achieves this?

hard

A. #!/bin/bash
apt-get update
apt-get install apache2 -y
mkdir /var/www/html
systemctl enable apache2
systemctl start apache2

B. #!/bin/bash
apt-get install apache2
mkdir /var/www/html
service apache2 stop

C. #!/bin/bash
apt-get update
apt-get install apache2 -y
mkdir -p /var/www/html
systemctl start apache2

D. #!/bin/bash
yum update -y
yum install apache2 -y
mkdir /var/www
systemctl restart apache2

Solution

1. Step 1: Verify package manager and commands

   For Debian-based VMs, apt-get is correct. Apache package is apache2. Creating /var/www/html is needed.

2. Step 2: Check service management commands

   #!/bin/bash apt-get update apt-get install apache2 -y mkdir /var/www/html systemctl enable apache2 systemctl start apache2 uses 'systemctl enable' to start Apache on boot and 'systemctl start' to start immediately, which is best practice.

3. Step 3: Compare other options

   #!/bin/bash apt-get update apt-get install apache2 -y mkdir -p /var/www/html systemctl start apache2 misses enabling service on boot. #!/bin/bash apt-get install apache2 mkdir /var/www/html service apache2 stop stops service instead of starting. #!/bin/bash yum update -y yum install apache2 -y mkdir /var/www systemctl restart apache2 uses yum (wrong for Debian).

4. Final Answer:

   #!/bin/bash apt-get update apt-get install apache2 -y mkdir /var/www/html systemctl enable apache2 systemctl start apache2 -> Option A

5. Quick Check:

   Enable and start service for automation [OK]

Hint: Enable and start services to run on boot in startup scripts [OK]

Common Mistakes:

• Forgetting to enable service to start on boot
• Using wrong package manager for the OS
• Stopping service instead of starting it