Minimum, maximum, and desired capacity in AWS - Step-by-Step Execution

Process Flow - Minimum, maximum, and desired capacity

Start Auto Scaling Group

↓

Check Desired Capacity

↓

Is Desired < Minimum?

Yes→Set Desired = Minimum

↓

Proceed

↓

Is Desired > Maximum?

Yes→Set Desired = Maximum

↓

Proceed

↓

Launch or Terminate Instances to Match Desired

↓

End

The system checks desired capacity against minimum and maximum limits, adjusts if needed, then launches or terminates instances to match desired capacity.

Execution Sample

AWS

MinCapacity=2
MaxCapacity=5
DesiredCapacity=6

if DesiredCapacity < MinCapacity:
    DesiredCapacity = MinCapacity
elif DesiredCapacity > MaxCapacity:
    DesiredCapacity = MaxCapacity

LaunchInstances(DesiredCapacity)

This code ensures desired capacity stays within min and max limits before launching instances.

Process Table

Step	Variable Checked	Condition	Action Taken	Resulting DesiredCapacity
1	DesiredCapacity=6	6 < 2?	No change	6
2	DesiredCapacity=6	6 > 5?	Set DesiredCapacity = 5	5
3	LaunchInstances	Launch 5 instances	Instances launched	5

💡 DesiredCapacity adjusted to max 5; 5 instances launched to match desired capacity.

Status Tracker

Variable	Start	After Step 1	After Step 2	Final
MinCapacity	2	2	2	2
MaxCapacity	5	5	5	5
DesiredCapacity	6	6	5	5

Key Moments - 2 Insights

Why does DesiredCapacity change from 6 to 5?

Because DesiredCapacity exceeded MaxCapacity (step 2 in execution_table), it was set down to MaxCapacity to respect the limit.

What happens if DesiredCapacity is less than MinCapacity?

DesiredCapacity is raised to MinCapacity to ensure minimum instances are running, similar to how it was capped at max in step 2.

Visual Quiz - 3 Questions

Look at the execution_table, what is DesiredCapacity after step 1?

A 2

B 5

C 6

D Undefined

💡 Hint

Check the 'Resulting DesiredCapacity' column in row for step 1.

At which step does DesiredCapacity get adjusted to respect limits?

A Step 1

B Step 2

C Step 3

D No adjustment

💡 Hint

Look for the step where 'Action Taken' changes DesiredCapacity.

If MinCapacity was 7 instead of 2, what would DesiredCapacity be after adjustments?

A 7

B 5

C 6

D Cannot determine

💡 Hint

Consider that DesiredCapacity must be at least MinCapacity, referencing variable_tracker logic.

Concept Snapshot

Minimum, maximum, and desired capacity control how many instances run.
Desired capacity is adjusted to be no less than minimum and no more than maximum.
AWS Auto Scaling launches or terminates instances to match the desired capacity.
This ensures resources are within set limits for cost and performance.

Full Transcript

In AWS Auto Scaling, you set three key numbers: minimum capacity, maximum capacity, and desired capacity. The system checks if the desired capacity is below the minimum or above the maximum. If it is, it adjusts the desired capacity to fit within those limits. Then it launches or terminates instances to match the adjusted desired capacity. For example, if desired capacity is 6 but maximum is 5, it lowers desired capacity to 5 and launches 5 instances. This keeps your resources balanced and controlled.