3-tier -> Security groups

main.tf

# Security group for app tier
resource "aws_security_group" "app-tier-sg" {
  name = "${var.vpc_name}-app-tier-sg"
  vpc_id = aws_vpc.main-vpc.id
  tags = {
    Name = "${var.vpc_name}-app-tier-sg"
  }

  ingress {
    from_port = 0
    to_port = 65535
    protocol = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }
  egress {
    from_port = 0
    to_port = 0
    protocol = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

# Security group for web tier
resource "aws_security_group" "web-subnet1-sg" {
  name = "${var.vpc_name}-web-tier-sg"
  vpc_id = aws_vpc.main-vpc.id
  tags = {
    Name = "${var.vpc_name}-web-tier-sg"
  }
}

resource "aws_security_group" "web-subnet2-sg" {
  name = "${var.vpc_name}-bastion-sg"
  vpc_id = aws_vpc.main-vpc.id
  tags = {
    Name = "${var.vpc_name}-bastion-sg"
  }
}

# Security group for db tier
resource "aws_security_group" "db-sg" {
  vpc_id = aws_vpc.main-vpc.id
egress {
    from_port = 0
    to_port = 0
    protocol = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
   ingress {
    from_port = 3306
    to_port = 3306
    protocol = "tcp"
    security_groups = [aws_security_group.app-tier-sg.id]
  }

  tags = {
    Name = "${var.vpc_name}-db-sg"
  }
}