Blue-green infrastructure pattern in Terraform - Step-by-Step Execution

Process Flow - Blue-green infrastructure pattern

Deploy Blue Environment

↓

Route Traffic to Blue

↓

Deploy Green Environment

↓

Switch Traffic to Green

↓

Blue Environment Idle

↓

Update or Rollback as Needed

This flow shows deploying two identical environments (blue and green), routing traffic to one while updating the other, then switching traffic to the updated environment.

Execution Sample

Terraform

resource "aws_instance" "blue" {
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

resource "aws_instance" "green" {
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

This Terraform code defines two identical AWS instances representing blue and green environments.

Process Table

Step	Action	Blue Environment State	Green Environment State	Traffic Routing
1	Deploy Blue Environment	Running	Not Deployed	Traffic to Blue
2	Deploy Green Environment	Running	Running	Traffic to Blue
3	Switch Traffic to Green	Running	Running	Traffic to Green
4	Blue Environment Idle	Running (Idle)	Running (Active)	Traffic to Green
5	Update or Rollback Blue	Updated or Rolled Back	Running (Active)	Traffic to Green
6	End	Stable	Stable	Traffic to Green

💡 Traffic switched to green environment; blue environment is idle and ready for updates or rollback.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	Final
Blue Environment	Not Deployed	Running	Running	Running	Running (Idle)	Updated or Rolled Back	Stable
Green Environment	Not Deployed	Not Deployed	Running	Running	Running (Active)	Running (Active)	Stable
Traffic Routing	None	Traffic to Blue	Traffic to Blue	Traffic to Green	Traffic to Green	Traffic to Green	Traffic to Green

Key Moments - 3 Insights

Why do we keep the old environment running after switching traffic?

Keeping the old environment running (see Step 4 in execution_table) allows quick rollback if the new environment has issues.

When is the green environment deployed?

The green environment is deployed after the blue is running (Step 2), so we have two identical environments before switching traffic.

How does traffic routing change during deployment?

Traffic is initially routed to blue (Steps 1 and 2), then switched to green (Step 3) once green is ready.

Visual Quiz - 3 Questions

Look at the execution_table, at which step does traffic switch to the green environment?

A Step 4

B Step 2

C Step 3

D Step 5

💡 Hint

Check the 'Traffic Routing' column in execution_table rows.

According to variable_tracker, what is the state of the blue environment after Step 5?

A Not Deployed

B Updated or Rolled Back

C Running (Active)

D Terminated

💡 Hint

Look at the 'Blue Environment' row under 'After Step 5' in variable_tracker.

If traffic was switched to green before deploying it, what would happen in the execution_table?

A Traffic would route to green while green is not running

B Blue environment would be idle earlier

C Green environment would be updated first

D Traffic would remain on blue

💡 Hint

Consider the 'Traffic Routing' and environment states in execution_table.

Concept Snapshot

Blue-green pattern deploys two identical environments.
Traffic routes to one (blue) while the other (green) is updated.
Switch traffic to green when ready.
Old environment stays idle for quick rollback.
Ensures zero downtime and safer updates.

Full Transcript

The blue-green infrastructure pattern involves deploying two identical environments called blue and green. Initially, traffic is routed to the blue environment while the green environment is deployed and updated. Once the green environment is ready, traffic switches to it, and the blue environment becomes idle but remains running. This setup allows quick rollback if needed by switching traffic back to blue. The pattern ensures zero downtime and safer updates by having two environments ready and switching traffic between them.