Scheduled scaling in AWS - Mini Project: Build & Apply

Scheduled Scaling with AWS Auto Scaling Group

📖 Scenario: You manage a web application hosted on AWS. To save costs during low traffic hours, you want to automatically reduce the number of servers running at night and increase them during the day.This is called scheduled scaling, where you set rules to change the number of servers at specific times.

🎯 Goal: Create an AWS Auto Scaling Group with a scheduled scaling policy that sets the desired capacity to 2 instances at 8 AM and scales down to 1 instance at 8 PM daily.

📋 What You'll Learn

Create an Auto Scaling Group named MyAppASG with a launch configuration named MyAppLaunchConfig.

Define a scheduled action named ScaleUpMorning to set desired capacity to 2 at 8 AM UTC daily.

Define a scheduled action named ScaleDownEvening to set desired capacity to 1 at 8 PM UTC daily.

💡 Why This Matters

🌍 Real World

Many companies use scheduled scaling to save money by running fewer servers during low traffic times, like nights or weekends.

💼 Career

Understanding scheduled scaling is important for cloud engineers and DevOps professionals to optimize cloud infrastructure costs and performance.

1

Create Launch Configuration

Create a launch configuration named MyAppLaunchConfig with the AMI ID ami-0abcdef1234567890 and instance type t2.micro.

AWS

# Your code here

Hint

The launch configuration defines the server image and size for your Auto Scaling Group.

2

Create Auto Scaling Group

Create an Auto Scaling Group named MyAppASG using the launch configuration MyAppLaunchConfig. Set the minimum size to 1, maximum size to 3, and desired capacity to 1. Use the availability zone us-east-1a.

AWS

resource "aws_launch_configuration" "MyAppLaunchConfig" {
  name          = "MyAppLaunchConfig"
  image_id      = "ami-0abcdef1234567890"
  instance_type = "t2.micro"
}

# Your code here

Hint

The Auto Scaling Group manages the number of instances running based on your settings.

3

Add Scheduled Scaling Action to Scale Up

Add a scheduled action named ScaleUpMorning to the Auto Scaling Group MyAppASG that sets the desired capacity to 2 at 8 AM UTC daily. Use the cron expression 0 8 * * *.

AWS

resource "aws_launch_configuration" "MyAppLaunchConfig" {
  name          = "MyAppLaunchConfig"
  image_id      = "ami-0abcdef1234567890"
  instance_type = "t2.micro"
}

resource "aws_autoscaling_group" "MyAppASG" {
  name                      = "MyAppASG"
  launch_configuration      = aws_launch_configuration.MyAppLaunchConfig.name
  min_size                  = 1
  max_size                  = 3
  desired_capacity          = 1
  availability_zones        = ["us-east-1a"]
}

# Your code here

Hint

Scheduled actions use cron expressions to run at specific times.

4

Add Scheduled Scaling Action to Scale Down

Add a scheduled action named ScaleDownEvening to the Auto Scaling Group MyAppASG that sets the desired capacity to 1 at 8 PM UTC daily. Use the cron expression 0 20 * * *.

AWS

resource "aws_launch_configuration" "MyAppLaunchConfig" {
  name          = "MyAppLaunchConfig"
  image_id      = "ami-0abcdef1234567890"
  instance_type = "t2.micro"
}

resource "aws_autoscaling_group" "MyAppASG" {
  name                      = "MyAppASG"
  launch_configuration      = aws_launch_configuration.MyAppLaunchConfig.name
  min_size                  = 1
  max_size                  = 3
  desired_capacity          = 1
  availability_zones        = ["us-east-1a"]
}

resource "aws_autoscaling_schedule" "ScaleUpMorning" {
  scheduled_action_name  = "ScaleUpMorning"
  autoscaling_group_name = aws_autoscaling_group.MyAppASG.name
  desired_capacity       = 2
  recurrence            = "0 8 * * *"
}

# Your code here

Hint

This scheduled action reduces the number of instances at night to save costs.

Practice

1. What is the main purpose of scheduled scaling in AWS?

easy

A. To automatically adjust resources at specific times

B. To manually increase server capacity when needed

C. To monitor security threats in real-time

D. To backup data at scheduled intervals

Solution

1. Step 1: Understand scheduled scaling concept

   Scheduled scaling is designed to change resource capacity automatically based on a set schedule.

2. Step 2: Compare options with the concept

   Only To automatically adjust resources at specific times describes automatic adjustment at specific times, matching scheduled scaling.

3. Final Answer:

   To automatically adjust resources at specific times -> Option A

4. Quick Check:

   Scheduled scaling = automatic timed resource adjustment [OK]

Hint: Scheduled scaling means automatic resource changes on a timer [OK]

Common Mistakes:

• Confusing scheduled scaling with manual scaling
• Thinking it handles security or backups
• Assuming it reacts only to traffic, not time

2. Which of the following is a valid cron expression for scheduled scaling in AWS?

easy

A. cron(0 0 0 0 ? *)

B. cron(60 24 * * ? *)

C. cron(* * * * *)

D. cron(0 12 * * ? *)

Solution

1. Step 1: Review cron expression format in AWS

   AWS cron expressions have six fields: minutes, hours, day-of-month, month, day-of-week, year.

2. Step 2: Validate each option

   cron(0 12 * * ? *) is valid: minute=0, hour=12, day-of-month=*, month=*, day-of-week=?, year=*. cron(0 0 0 0 ? *) has invalid zero day-of-month and month values. cron(60 24 * * ? *) has invalid 60 minutes and 24 hours. cron(* * * * *) has only five fields, missing year.

3. Final Answer:

   cron(0 12 * * ? *) -> Option D

4. Quick Check:

   Valid AWS cron = 6 fields, correct ranges [OK]

Hint: AWS cron needs 6 fields with valid ranges [OK]

Common Mistakes:

• Using 5-field cron instead of 6-field
• Setting minutes or hours out of range
• Confusing day-of-week and day-of-month

3. Given this scheduled scaling configuration snippet:

{"ScheduledActionName": "ScaleUpMorning", "StartTime": "2024-07-01T08:00:00Z", "DesiredCapacity": 5}

What will happen at 8 AM UTC on July 1, 2024?

medium

A. The resource capacity will be set to 5

B. The resource capacity will decrease to 0

C. The scaling action will be ignored due to missing EndTime

D. The resource capacity will remain unchanged

Solution

1. Step 1: Understand the scheduled action parameters

   The action named "ScaleUpMorning" is set to start at 8 AM UTC on July 1, 2024, with DesiredCapacity 5.

2. Step 2: Interpret the effect of StartTime and DesiredCapacity

   At the StartTime, the capacity will be set to 5. EndTime is optional and does not block the action.

3. Final Answer:

   The resource capacity will be set to 5 -> Option A

4. Quick Check:

   StartTime triggers capacity change to DesiredCapacity [OK]

Hint: StartTime sets capacity; EndTime is optional [OK]

Common Mistakes:

• Thinking EndTime is required to trigger scaling
• Assuming capacity decreases without explicit setting
• Ignoring the StartTime effect

4. You created a scheduled scaling action with this cron expression:
cron(0 25 * * ? *)
Why does the scaling not trigger as expected?

medium

A. The day-of-week field is missing

B. The minute value 0 is invalid

C. The hour value 25 is invalid in cron expressions

D. The cron expression needs only 5 fields

Solution

1. Step 1: Check the hour field in the cron expression

   The hour field is set to 25, but valid hour values are 0 to 23.

2. Step 2: Understand cron validation rules in AWS

   AWS rejects cron expressions with invalid field values, so the scaling action won't trigger.

3. Final Answer:

   The hour value 25 is invalid in cron expressions -> Option C

4. Quick Check:

   Hour must be 0-23 in AWS cron [OK]

Hint: Check cron field ranges; hours max 23 [OK]

Common Mistakes:

• Assuming minute 0 is invalid
• Thinking day-of-week is mandatory
• Using 5 fields instead of 6

5. You want to reduce your AWS Auto Scaling group capacity to 2 instances every night at 11 PM UTC and increase it to 10 instances every weekday morning at 7 AM UTC. Which setup correctly uses scheduled scaling to achieve this?

hard

A. Create one scheduled action with cron(0 23,7 * * ? *) setting DesiredCapacity=2 and DesiredCapacity=10

B. Create two scheduled actions: one with cron(0 23 * * ? *) setting DesiredCapacity=2, another with cron(0 7 ? * MON-FRI *) setting DesiredCapacity=10

C. Create two scheduled actions: one with rate(1 day) setting DesiredCapacity=2, another with rate(1 hour) setting DesiredCapacity=10

D. Create one scheduled action with cron(0 7 * * ? *) setting DesiredCapacity=10 only

Solution

1. Step 1: Understand the scheduling requirements

   Capacity should be 2 at 11 PM daily and 10 at 7 AM on weekdays only.

2. Step 2: Match cron expressions to requirements

   cron(0 23 * * ? *) runs daily at 11 PM; cron(0 7 ? * MON-FRI *) runs at 7 AM Monday to Friday. Two separate scheduled actions are needed with correct DesiredCapacity values.

3. Final Answer:

   Create two scheduled actions: one with cron(0 23 * * ? *) setting DesiredCapacity=2, another with cron(0 7 ? * MON-FRI *) setting DesiredCapacity=10 -> Option B

4. Quick Check:

   Separate cron for each time and capacity [OK]

Hint: Use separate scheduled actions with correct cron and capacity [OK]

Common Mistakes:

• Trying to set two capacities in one scheduled action
• Using rate expressions instead of cron for weekdays
• Missing weekday restriction for morning scale-up