AWS VPC子网IP地址变更（解决客户IP冲突）技术问询

Got it, let's walk through this step by step—dealing with IP conflicts between your AWS VPC and a customer's data center over Direct Connect is a common scenario, but we need to be methodical to avoid downtime. Here's a structured approach to resolve the conflict and update all dependent components:

• First, audit all resources using the conflicting IP range—this includes EC2 instances, RDS databases, Lambda functions with VPC access, load balancers, and any other resources assigned IPs from the problematic subnet. Use the AWS CLI to quickly list affected instances:

  aws ec2 describe-instances --filters "Name=private-ip-address,Values=192.168.X.0/24"  # Replace with your conflicting CIDR
  

• Notify all stakeholders (including the customer) about a planned maintenance window—modifying subnets and routes will cause brief downtime for resources in the conflicting range.
• Take snapshots of critical resources (EC2 volumes, RDS instances) and export current route table configurations as a backup:

  aws ec2 describe-route-tables --filters "Name=vpc-id,Values=vpc-XXXXXX" > route-table-backup.json
  

• Migrate all running resources from the conflicting subnet to a temporary non-conflicting subnet in the same VPC (if available). For stateful services like databases, use point-in-time restores to spin up copies in a safe subnet.
• Once all resources are moved, delete the conflicting subnet:

  aws ec2 delete-subnet --subnet-id subnet-XXXXXX
  

• Double-check for lingering elastic network interfaces (ENIs) tied to the deleted subnet—clean them up if found:

  aws ec2 describe-network-interfaces --filters "Name=subnet-id,Values=subnet-XXXXXX"
  

• Create a new subnet with your chosen non-conflicting CIDR. If the new CIDR falls outside your VPC's current range, expand the VPC first:

  aws ec2 modify-vpc-cidr-block --vpc-id vpc-XXXXXX --cidr-block 10.0.X.0/24  # Replace with your new CIDR
  

• Configure subnet settings: assign the correct route table (we'll update this next), enable auto-assign public IP if needed, and associate security groups used with the old subnet.
• Migrate temporary resources to this new subnet, or deploy new resources here as required.

• VPC Route Tables: Remove routes pointing to the old conflicting CIDR, then add a new route for the new subnet to your Direct Connect gateway (DXGW) or virtual private gateway (VGW):

  aws ec2 create-route --route-table-id rtb-XXXXXX --destination-cidr-block 10.0.X.0/24 --gateway-id dxgw-XXXXXX
  

• Customer On-Prem Routes: Coordinate with the customer's network team to update their data center route tables—remove the old conflicting CIDR and add the new subnet's range, pointing traffic to your Direct Connect connection.
• Transit Gateway (if used): If you're using a Transit Gateway to connect multiple VPCs, update its route tables to reflect the new CIDR and remove the old entry.

• Test end-to-end connectivity: from an EC2 instance in the new subnet, run ping or traceroute to a customer on-prem IP, and have the customer test the reverse.
• Check AWS CloudWatch metrics for Direct Connect to confirm no errors or dropped packets.
• Verify all migrated resources function as expected—test application workflows that rely on cross-connectivity.

• Delete any temporary resources (like the migration subnet) once everything is stable.
• Update internal documentation with the new subnet CIDR and route table configurations.
• Conduct a post-maintenance check-in with the customer to confirm they have no remaining issues.

内容的提问来源于stack exchange，提问作者maghes elango