How to import existing VPC in aws cdk?

For AWS CDK v2 or v1(latest), You can use:

// You can either use vpcId OR vpcName and fetch the desired vpc
const getExistingVpc = ec2.Vpc.fromLookup(this, 'ImportVPC',{
      vpcId: "VPC_ID",
      vpcName: "VPC_NAME"
});

Take a look at aws_cdk.aws_ec2 documentation and at CDK Runtime Context.

If your VPC is created outside your CDK app, you can use Vpc.fromLookup(). The CDK CLI will search for the specified VPC in the the stack’s region and account, and import the subnet configuration. Looking up can be done by VPC ID, but more flexibly by searching for a specific tag on the VPC.

Usage:

# Example automatically generated. See https://github.com/aws/jsii/issues/826
from aws_cdk.core import App, Stack, Environment
from aws_cdk import aws_ec2 as ec2

# Information from environment is used to get context information
# so it has to be defined for the stack
stack = MyStack(
    app, "MyStack", env=Environment(account="account_id", region="region")
)

# Retrieve VPC information
vpc = ec2.Vpc.from_lookup(stack, "VPC",
    # This imports the default VPC but you can also
    # specify a 'vpcName' or 'tags'.
    is_default=True
)

Update with a relevant example:

vpc = ec2.Vpc.from_lookup(stack, "VPC",
    vpc_id = VPC_ID
)

Update with typescript example:

import ec2 = require('@aws-cdk/aws-ec2');
const getExistingVpc = ec2.Vpc.fromLookup(this, 'ImportVPC',{isDefault: true});

More info here.