# Getting started with Amazon VPC Transit Gateway
<a name="example_vpc_TransitGatewayGettingStarted_section"></a>

The following code example shows how to:
+ Create a transit gateway
+ Attach your VPCs to your transit gateway
+ Add routes between the transit gateway and your VPCs
+ Test the transit gateway
+ Clean up resources

------
#### [ Bash ]

**Amazon CLI with Bash script**  
 There's more on GitHub. Find the complete example and learn how to set up and run in the [Sample developer tutorials](https://github.com/aws-samples/sample-developer-tutorials/tree/main/tuts/012-transitgateway-gettingstarted) repository. 

```
#!/bin/bash

# Amazon VPC Transit Gateway CLI Script
# This script demonstrates how to create a transit gateway and connect two VPCs
# Modified to work with older AWS CLI versions that don't support transit gateway wait commands
# Security improved: Added input validation, error handling, and credential checks

# Error handling
set -euo pipefail
LOG_FILE="transit-gateway-tutorial.log"
exec > >(tee -a "$LOG_FILE") 2>&1

# Security: Check for required AWS credentials
if ! aws sts get-caller-identity &>/dev/null; then
  echo "ERROR: AWS credentials not configured or invalid. Please configure AWS credentials."
  exit 1
fi

# Function to validate AWS CLI output
validate_aws_output() {
  local output=$1
  local context=$2
  
  if [ -z "$output" ] || [ "$output" = "None" ]; then
    echo "ERROR: Failed to retrieve $context from AWS API"
    return 1
  fi
}

# Function to validate CIDR blocks
validate_cidr() {
  local cidr=$1
  if ! [[ "$cidr" =~ ^([0-9]{1,3}\.){3}[0-9]{1,3}/[0-9]{1,2}$ ]]; then
    echo "ERROR: Invalid CIDR block format: $cidr"
    return 1
  fi
}

# Function to wait for transit gateway to be available
wait_for_tgw() {
  local tgw_id=$1
  local max_attempts=60
  local attempt=0
  
  echo "Waiting for Transit Gateway $tgw_id to become available..."
  
  while [ $attempt -lt $max_attempts ]; do
    status=$(aws ec2 describe-transit-gateways \
      --transit-gateway-ids "$tgw_id" \
      --query "TransitGateways[0].State" \
      --output text 2>/dev/null || echo "failed")
    
    echo "Current status: $status"
    
    if [ "$status" = "available" ]; then
      echo "Transit Gateway is now available"
      return 0
    fi
    
    if [ "$status" = "failed" ]; then
      echo "ERROR: Transit Gateway creation failed"
      return 1
    fi
    
    echo "Waiting for transit gateway to become available. Current state: $status"
    sleep 10
    ((attempt++))
  done
  
  echo "ERROR: Timeout waiting for transit gateway to become available"
  return 1
}

# Function to wait for transit gateway attachment to be available
wait_for_tgw_attachment() {
  local attachment_id=$1
  local max_attempts=60
  local attempt=0
  
  echo "Waiting for Transit Gateway Attachment $attachment_id to become available..."
  
  while [ $attempt -lt $max_attempts ]; do
    status=$(aws ec2 describe-transit-gateway-vpc-attachments \
      --transit-gateway-attachment-ids "$attachment_id" \
      --query "TransitGatewayVpcAttachments[0].State" \
      --output text 2>/dev/null || echo "failed")
    
    echo "Current status: $status"
    
    if [ "$status" = "available" ]; then
      echo "Transit Gateway Attachment is now available"
      return 0
    fi
    
    if [ "$status" = "failed" ]; then
      echo "ERROR: Transit Gateway Attachment creation failed"
      return 1
    fi
    
    echo "Waiting for transit gateway attachment to become available. Current state: $status"
    sleep 10
    ((attempt++))
  done
  
  echo "ERROR: Timeout waiting for transit gateway attachment to become available"
  return 1
}

# Function to wait for transit gateway attachment to be deleted
wait_for_tgw_attachment_deleted() {
  local attachment_id=$1
  local max_attempts=60
  local attempt=0
  
  echo "Waiting for Transit Gateway Attachment $attachment_id to be deleted..."
  
  while [ $attempt -lt $max_attempts ]; do
    count=$(aws ec2 describe-transit-gateway-vpc-attachments \
      --filters "Name=transit-gateway-attachment-id,Values=$attachment_id" \
      --query "length(TransitGatewayVpcAttachments)" \
      --output text 2>/dev/null || echo "0")
    
    if [ "$count" = "0" ]; then
      echo "Transit Gateway Attachment has been deleted"
      return 0
    fi
    
    status=$(aws ec2 describe-transit-gateway-vpc-attachments \
      --transit-gateway-attachment-ids "$attachment_id" \
      --query "TransitGatewayVpcAttachments[0].State" \
      --output text 2>/dev/null || echo "deleted")
    
    if [ "$status" = "deleted" ] || [ "$status" = "deleting" ]; then
      echo "Transit Gateway Attachment is being deleted. Current state: $status"
    fi
    
    echo "Waiting for transit gateway attachment to be deleted. Current state: $status"
    sleep 10
    ((attempt++))
  done
  
  echo "WARNING: Timeout waiting for transit gateway attachment to be deleted"
  return 0
}

# Function to clean up resources
cleanup() {
  local exit_code=$?
  echo "Error occurred (exit code: $exit_code). Cleaning up resources..."
  
  # Delete resources in reverse order
  if [ -n "${TGW_ATTACHMENT_1_ID:-}" ]; then
    echo "Deleting Transit Gateway VPC Attachment 1: $TGW_ATTACHMENT_1_ID"
    aws ec2 delete-transit-gateway-vpc-attachment \
      --transit-gateway-attachment-id "$TGW_ATTACHMENT_1_ID" &>/dev/null || true
    wait_for_tgw_attachment_deleted "$TGW_ATTACHMENT_1_ID" || true
  fi
  
  if [ -n "${TGW_ATTACHMENT_2_ID:-}" ]; then
    echo "Deleting Transit Gateway VPC Attachment 2: $TGW_ATTACHMENT_2_ID"
    aws ec2 delete-transit-gateway-vpc-attachment \
      --transit-gateway-attachment-id "$TGW_ATTACHMENT_2_ID" &>/dev/null || true
    wait_for_tgw_attachment_deleted "$TGW_ATTACHMENT_2_ID" || true
  fi
  
  if [ -n "${TGW_ID:-}" ]; then
    echo "Deleting Transit Gateway: $TGW_ID"
    aws ec2 delete-transit-gateway --transit-gateway-id "$TGW_ID" &>/dev/null || true
  fi
  
  exit "$exit_code"
}

# Set up trap for error handling
trap cleanup EXIT

echo "=== Amazon VPC Transit Gateway Tutorial ==="
echo "This script will create a transit gateway and connect two VPCs"
echo ""

# Get a valid availability zone dynamically
echo "Getting available AZ in current region..."
AZ=$(aws ec2 describe-availability-zones \
  --query "AvailabilityZones[0].ZoneName" \
  --output text)
validate_aws_output "$AZ" "availability zone" || exit 1
echo "Using availability zone: $AZ"

# Check if VPCs exist
echo "Checking for existing VPCs..."
VPC1_ID=$(aws ec2 describe-vpcs \
  --filters "Name=tag:Name,Values=VPC1" \
  --query "Vpcs[0].VpcId" \
  --output text)
VPC2_ID=$(aws ec2 describe-vpcs \
  --filters "Name=tag:Name,Values=VPC2" \
  --query "Vpcs[0].VpcId" \
  --output text)

if [ "$VPC1_ID" = "None" ] || [ -z "$VPC1_ID" ]; then
  echo "Creating VPC1..."
  VPC1_ID=$(aws ec2 create-vpc \
    --cidr-block 10.1.0.0/16 \
    --tag-specifications 'ResourceType=vpc,Tags=[{Key=Name,Value=VPC1},{Key=project,Value=doc-smith},{Key=tutorial,Value=transitgateway-gettingstarted}]' \
    --query Vpc.VpcId \
    --output text)
  validate_aws_output "$VPC1_ID" "VPC1" || exit 1
  echo "Created VPC1: $VPC1_ID"
  
  # Create a subnet in VPC1
  echo "Creating subnet in VPC1..."
  SUBNET1_ID=$(aws ec2 create-subnet \
    --vpc-id "$VPC1_ID" \
    --cidr-block 10.1.0.0/24 \
    --availability-zone "$AZ" \
    --tag-specifications 'ResourceType=subnet,Tags=[{Key=Name,Value=VPC1-Subnet},{Key=project,Value=doc-smith},{Key=tutorial,Value=transitgateway-gettingstarted}]' \
    --query Subnet.SubnetId \
    --output text)
  validate_aws_output "$SUBNET1_ID" "VPC1 subnet" || exit 1
  echo "Created subnet in VPC1: $SUBNET1_ID"
else
  echo "Using existing VPC1: $VPC1_ID"
  SUBNET1_ID=$(aws ec2 describe-subnets \
    --filters "Name=vpc-id,Values=$VPC1_ID" \
    --query "Subnets[0].SubnetId" \
    --output text)
  if [ "$SUBNET1_ID" = "None" ] || [ -z "$SUBNET1_ID" ]; then
    echo "Creating subnet in VPC1..."
    SUBNET1_ID=$(aws ec2 create-subnet \
      --vpc-id "$VPC1_ID" \
      --cidr-block 10.1.0.0/24 \
      --availability-zone "$AZ" \
      --tag-specifications 'ResourceType=subnet,Tags=[{Key=Name,Value=VPC1-Subnet},{Key=project,Value=doc-smith},{Key=tutorial,Value=transitgateway-gettingstarted}]' \
      --query Subnet.SubnetId \
      --output text)
    validate_aws_output "$SUBNET1_ID" "VPC1 subnet" || exit 1
    echo "Created subnet in VPC1: $SUBNET1_ID"
  else
    echo "Using existing subnet in VPC1: $SUBNET1_ID"
  fi
fi

if [ "$VPC2_ID" = "None" ] || [ -z "$VPC2_ID" ]; then
  echo "Creating VPC2..."
  VPC2_ID=$(aws ec2 create-vpc \
    --cidr-block 10.2.0.0/16 \
    --tag-specifications 'ResourceType=vpc,Tags=[{Key=Name,Value=VPC2},{Key=project,Value=doc-smith},{Key=tutorial,Value=transitgateway-gettingstarted}]' \
    --query Vpc.VpcId \
    --output text)
  validate_aws_output "$VPC2_ID" "VPC2" || exit 1
  echo "Created VPC2: $VPC2_ID"
  
  # Create a subnet in VPC2
  echo "Creating subnet in VPC2..."
  SUBNET2_ID=$(aws ec2 create-subnet \
    --vpc-id "$VPC2_ID" \
    --cidr-block 10.2.0.0/24 \
    --availability-zone "$AZ" \
    --tag-specifications 'ResourceType=subnet,Tags=[{Key=Name,Value=VPC2-Subnet},{Key=project,Value=doc-smith},{Key=tutorial,Value=transitgateway-gettingstarted}]' \
    --query Subnet.SubnetId \
    --output text)
  validate_aws_output "$SUBNET2_ID" "VPC2 subnet" || exit 1
  echo "Created subnet in VPC2: $SUBNET2_ID"
else
  echo "Using existing VPC2: $VPC2_ID"
  SUBNET2_ID=$(aws ec2 describe-subnets \
    --filters "Name=vpc-id,Values=$VPC2_ID" \
    --query "Subnets[0].SubnetId" \
    --output text)
  if [ "$SUBNET2_ID" = "None" ] || [ -z "$SUBNET2_ID" ]; then
    echo "Creating subnet in VPC2..."
    SUBNET2_ID=$(aws ec2 create-subnet \
      --vpc-id "$VPC2_ID" \
      --cidr-block 10.2.0.0/24 \
      --availability-zone "$AZ" \
      --tag-specifications 'ResourceType=subnet,Tags=[{Key=Name,Value=VPC2-Subnet},{Key=project,Value=doc-smith},{Key=tutorial,Value=transitgateway-gettingstarted}]' \
      --query Subnet.SubnetId \
      --output text)
    validate_aws_output "$SUBNET2_ID" "VPC2 subnet" || exit 1
    echo "Created subnet in VPC2: $SUBNET2_ID"
  else
    echo "Using existing subnet in VPC2: $SUBNET2_ID"
  fi
fi

# Get route tables for each VPC
RTB1_ID=$(aws ec2 describe-route-tables \
  --filters "Name=vpc-id,Values=$VPC1_ID" \
  --query "RouteTables[0].RouteTableId" \
  --output text)
validate_aws_output "$RTB1_ID" "VPC1 route table" || exit 1

RTB2_ID=$(aws ec2 describe-route-tables \
  --filters "Name=vpc-id,Values=$VPC2_ID" \
  --query "RouteTables[0].RouteTableId" \
  --output text)
validate_aws_output "$RTB2_ID" "VPC2 route table" || exit 1

echo "Route table for VPC1: $RTB1_ID"
echo "Route table for VPC2: $RTB2_ID"

# Step 1: Create the transit gateway
echo "Creating Transit Gateway..."
TGW_ID=$(aws ec2 create-transit-gateway \
  --description "My Transit Gateway" \
  --options "AmazonSideAsn=64512,AutoAcceptSharedAttachments=disable,DefaultRouteTableAssociation=enable,DefaultRouteTablePropagation=enable,VpnEcmpSupport=enable,DnsSupport=enable,MulticastSupport=disable" \
  --tag-specifications 'ResourceType=transit-gateway,Tags=[{Key=Name,Value=MyTransitGateway},{Key=project,Value=doc-smith},{Key=tutorial,Value=transitgateway-gettingstarted}]' \
  --query TransitGateway.TransitGatewayId \
  --output text)
validate_aws_output "$TGW_ID" "Transit Gateway" || exit 1
echo "Created Transit Gateway: $TGW_ID"

# Wait for the transit gateway to become available
wait_for_tgw "$TGW_ID" || exit 1

# Step 2: Attach VPCs to the transit gateway
echo "Attaching VPC1 to Transit Gateway..."
TGW_ATTACHMENT_1_ID=$(aws ec2 create-transit-gateway-vpc-attachment \
  --transit-gateway-id "$TGW_ID" \
  --vpc-id "$VPC1_ID" \
  --subnet-ids "$SUBNET1_ID" \
  --tag-specifications 'ResourceType=transit-gateway-attachment,Tags=[{Key=Name,Value=VPC1-Attachment},{Key=project,Value=doc-smith},{Key=tutorial,Value=transitgateway-gettingstarted}]' \
  --query TransitGatewayVpcAttachment.TransitGatewayAttachmentId \
  --output text)
validate_aws_output "$TGW_ATTACHMENT_1_ID" "Transit Gateway VPC1 Attachment" || exit 1
echo "Created Transit Gateway VPC Attachment for VPC1: $TGW_ATTACHMENT_1_ID"

echo "Attaching VPC2 to Transit Gateway..."
TGW_ATTACHMENT_2_ID=$(aws ec2 create-transit-gateway-vpc-attachment \
  --transit-gateway-id "$TGW_ID" \
  --vpc-id "$VPC2_ID" \
  --subnet-ids "$SUBNET2_ID" \
  --tag-specifications 'ResourceType=transit-gateway-attachment,Tags=[{Key=Name,Value=VPC2-Attachment},{Key=project,Value=doc-smith},{Key=tutorial,Value=transitgateway-gettingstarted}]' \
  --query TransitGatewayVpcAttachment.TransitGatewayAttachmentId \
  --output text)
validate_aws_output "$TGW_ATTACHMENT_2_ID" "Transit Gateway VPC2 Attachment" || exit 1
echo "Created Transit Gateway VPC Attachment for VPC2: $TGW_ATTACHMENT_2_ID"

# Wait for the attachments to become available
wait_for_tgw_attachment "$TGW_ATTACHMENT_1_ID" || exit 1
wait_for_tgw_attachment "$TGW_ATTACHMENT_2_ID" || exit 1

# Step 3: Add routes between the transit gateway and VPCs
echo "Adding route from VPC1 to VPC2 via Transit Gateway..."
validate_cidr "10.2.0.0/16" || exit 1
aws ec2 create-route \
  --route-table-id "$RTB1_ID" \
  --destination-cidr-block 10.2.0.0/16 \
  --transit-gateway-id "$TGW_ID" || exit 1

echo "Adding route from VPC2 to VPC1 via Transit Gateway..."
validate_cidr "10.1.0.0/16" || exit 1
aws ec2 create-route \
  --route-table-id "$RTB2_ID" \
  --destination-cidr-block 10.1.0.0/16 \
  --transit-gateway-id "$TGW_ID" || exit 1

echo "Routes added successfully"

# Step 4: Display information for testing
echo ""
echo "=== Transit Gateway Setup Complete ==="
echo "Transit Gateway ID: $TGW_ID"
echo "VPC1 ID: $VPC1_ID"
echo "VPC2 ID: $VPC2_ID"
echo ""
echo "To test connectivity:"
echo "1. Launch an EC2 instance in each VPC"
echo "2. Configure security groups to allow ICMP traffic"
echo "3. Connect to one instance and ping the other instance's private IP"
echo ""

echo "Viewing created resources..."

echo ""
echo "=== Resources Created ==="
echo "Transit Gateway: $TGW_ID"
echo "VPC1: $VPC1_ID"
echo "VPC2: $VPC2_ID"
echo "Subnet in VPC1: $SUBNET1_ID"
echo "Subnet in VPC2: $SUBNET2_ID"
echo "Transit Gateway Attachment for VPC1: $TGW_ATTACHMENT_1_ID"
echo "Transit Gateway Attachment for VPC2: $TGW_ATTACHMENT_2_ID"
echo ""

echo "Starting cleanup..."

# Delete routes
echo "Deleting routes..."
aws ec2 delete-route --route-table-id "$RTB1_ID" --destination-cidr-block 10.2.0.0/16 || true
aws ec2 delete-route --route-table-id "$RTB2_ID" --destination-cidr-block 10.1.0.0/16 || true

# Delete transit gateway attachments
echo "Deleting Transit Gateway VPC Attachment for VPC1: $TGW_ATTACHMENT_1_ID"
aws ec2 delete-transit-gateway-vpc-attachment \
  --transit-gateway-attachment-id "$TGW_ATTACHMENT_1_ID" || true

echo "Deleting Transit Gateway VPC Attachment for VPC2: $TGW_ATTACHMENT_2_ID"
aws ec2 delete-transit-gateway-vpc-attachment \
  --transit-gateway-attachment-id "$TGW_ATTACHMENT_2_ID" || true

# Wait for attachments to be deleted
wait_for_tgw_attachment_deleted "$TGW_ATTACHMENT_1_ID" || true
wait_for_tgw_attachment_deleted "$TGW_ATTACHMENT_2_ID" || true

# Delete transit gateway
echo "Deleting Transit Gateway: $TGW_ID"
aws ec2 delete-transit-gateway --transit-gateway-id "$TGW_ID" || true

echo "Cleanup completed successfully"

echo "Tutorial completed. See $LOG_FILE for detailed logs."
```
+ For API details, see the following topics in *Amazon CLI Command Reference*.
  + [CreateRoute](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/CreateRoute)
  + [CreateSubnet](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/CreateSubnet)
  + [CreateTransitGateway](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/CreateTransitGateway)
  + [CreateTransitGatewayVpcAttachment](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/CreateTransitGatewayVpcAttachment)
  + [CreateVpc](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/CreateVpc)
  + [DeleteRoute](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/DeleteRoute)
  + [DeleteTransitGateway](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/DeleteTransitGateway)
  + [DeleteTransitGatewayVpcAttachment](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/DeleteTransitGatewayVpcAttachment)
  + [DescribeAvailabilityZones](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/DescribeAvailabilityZones)
  + [DescribeRouteTables](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/DescribeRouteTables)
  + [DescribeSubnets](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/DescribeSubnets)
  + [DescribeTransitGatewayAttachments](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/DescribeTransitGatewayAttachments)
  + [DescribeTransitGatewayVpcAttachments](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/DescribeTransitGatewayVpcAttachments)
  + [DescribeTransitGateways](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/DescribeTransitGateways)
  + [DescribeVpcs](https://docs.amazonaws.cn/goto/aws-cli/ec2-2016-11-15/DescribeVpcs)

------

For a complete list of Amazon SDK developer guides and code examples, see [Create Amazon EC2 resources using an Amazon SDK](sdk-general-information-section.md). This topic also includes information about getting started and details about previous SDK versions.