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Aisalkyn Aidarova
Aisalkyn Aidarova

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PRODUCTION LAB — Using `user_data` (BEST PRACTICE)

#aws #automation #terraform #devops

Instead of:

Terraform → SSH → install nginx
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We use:

Terraform → EC2 boots → user_data runs automatically
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👉 No SSH
👉 No keys
👉 Faster
👉 Production-ready

📁 Folder structure 

terraform-userdata/
└── main.tf
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✅ FULL main.tf (COPY EXACTLY) 

provider "aws" {
  region = "us-east-2"
}

# -----------------------------
# GET LATEST AMAZON LINUX AMI
# -----------------------------
data "aws_ami" "amazon_linux" {
  most_recent = true
  owners      = ["amazon"]

  filter {
    name   = "name"
    values = ["amzn2-ami-hvm-*-x86_64-gp2"]
  }
}

# -----------------------------
# SECURITY GROUP
# -----------------------------
resource "aws_security_group" "web_sg" {
  name = "userdata-sg"

  ingress {
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  # ❗ Notice: NO SSH (port 22 removed)

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

# -----------------------------
# EC2 INSTANCE (NO KEY, NO SSH)
# -----------------------------
resource "aws_instance" "web" {
  ami           = data.aws_ami.amazon_linux.id
  instance_type = "t2.micro"

  vpc_security_group_ids = [aws_security_group.web_sg.id]

  # -----------------------------
  # USER DATA (RUNS AT BOOT)
  # -----------------------------
  user_data = <<-EOF
              #!/bin/bash
              yum update -y
              yum install -y httpd
              systemctl start httpd
              systemctl enable httpd
              echo "<h1>Welcome from Terraform User Data</h1>" > /var/www/html/index.html
              EOF

  tags = {
    Name = "userdata-lab"
  }
}
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🚀 STEP-BY-STEP

1. Create folder 

mkdir terraform-userdata
cd terraform-userdata
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2. Create file 

touch main.tf
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Paste code.

3. Run Terraform 

terraform init
terraform apply -auto-approve
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🔍 VERIFY

Step 1 — Get Public IP

From Terraform output or AWS console

Step 2 — Open browser 

http://<PUBLIC_IP>
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👉 You will see:

Welcome from Terraform User Data
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🔥 WHAT HAPPENED (IMPORTANT)

When EC2 started:

  1. AWS executed user_data
  2. Installed Apache
  3. Started service
  4. Created webpage

👉 No SSH
👉 No provisioners
👉 Fully automatic

⚡ Compare (VERY IMPORTANT )

Feature Provisioner user_data
SSH needed Yes No
Key needed Yes No
Runs when After creation At boot
Production ❌ Avoid ✅ Standard
Speed Slower Faster
Reliability Medium High

🎤 Interview Answer (GOLD)

We use user_data in production because it runs automatically during instance initialization, does not require SSH, and provides a more reliable and scalable way to configure instances compared to provisioners.

🧠 Real Production Flow 

Terraform → create EC2
        → EC2 boots
        → user_data runs automatically
        → application ready
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🎯 FINAL TAKEAWAY

Provisioners = learning tool
user_data = real production standard

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