Profile Applicability:
Level 1
Description:
Amazon Route 53 is a scalable Domain Name System (DNS) web service that routes end users to infrastructure running in AWS. When managing DNS records in Route 53, it is crucial to ensure that the IP addresses referenced by the DNS records (e.g., A records, AAAA records) are valid and in use. Dangling IPs refer to IP addresses that are no longer associated with active resources (e.g., EC2 instances, load balancers), which may result in users being unable to reach the intended resource.
This SOP ensures that Route 53 DNS records do not contain dangling IPs, which could cause downtime, misrouting, or customer frustration. It involves identifying and verifying that IP addresses in Route 53 records are valid and still associated with live AWS resources.
Rationale:
Ensuring that Route 53 records do not contain dangling IPs is essential for:
Avoiding Misrouting: Prevents users from being directed to non-existent or decommissioned resources.
Improved Reliability: Ensures that DNS records are always pointing to active and correct resources, improving the user experience.
Cost Optimization: Identifying and removing obsolete DNS records helps reduce the risk of directing traffic to unused resources, preventing unnecessary costs.
Security: Ensures that DNS records are pointing to the correct resources, reducing the risk of directing traffic to unauthorized or compromised systems.
Impact:
Pros:
Improved Service Availability: Ensures that DNS records point to valid, active resources, reducing downtime or connectivity issues.
Reduced Errors: Helps avoid scenarios where traffic is directed to old or incorrect IP addresses.
Optimized Resource Management: By cleaning up unused DNS records, you ensure that the correct resources are always in use.
Cons:
Manual Verification: Requires manual or automated checks to ensure that all IPs in DNS records are valid and active.
Initial Effort: The initial task of verifying DNS records may require significant resources, especially if there are many records to check.
Default Value:
By default, Route 53 does not automatically remove DNS records for decommissioned or unused IP addresses. These records need to be manually checked for validity.
Pre-requisite:
AWS IAM Permissions:
route53:ListResourceRecordSets
route53:ChangeResourceRecordSets
ec2:DescribeInstances
ec2:DescribeNetworkInterfaces
AWS CLI installed and configured.
Access to Route 53 hosted zones and EC2 instances.
Basic knowledge of DNS records and AWS resource management.
Remediation:
Test Plan:
Using AWS Console:
Sign in to the AWS Management Console.
Navigate to Route 53 under Services.
In the Route 53 Dashboard, go to Hosted Zones.
For each hosted zone, review the Resource Record Sets (e.g., A records, AAAA records) and note the IP addresses in use.
For each IP address, check if it is associated with an active EC2 instance, Elastic Load Balancer (ELB), or any other AWS service. You can do this by:
Navigating to EC2 > Instances or Elastic Load Balancers.
Cross-referencing the IPs listed in Route 53 with the ones active in your AWS resources.
If any DNS record points to an IP address that is not associated with an active resource, consider removing or updating the record.
Using AWS CLI:
To list Route 53 records, run:
aws route53 list-resource-record-sets --hosted-zone-id <hosted-zone-id>
Review the output for A records and AAAA records, noting the IP addresses in use.
To check if an EC2 instance is associated with a specific IP, run:
aws ec2 describe-instances --filters "Name=private-ip-address,Values=<ip-address>"
If the IP is not found in any EC2 instance, check for associated Elastic IPs or load balancers using similar queries for Elastic Load Balancers or Elastic IPs.
If the IP does not correspond to any active resource, it may be a dangling IP, and the DNS record should be updated or removed.
Implementation Steps:
Using AWS Console:
Sign in to the AWS Management Console and navigate to Route 53.
Go to Hosted Zones and select the hosted zone that contains the records you want to check.
Review the Resource Record Sets to identify any A or AAAA records that contain IP addresses.
Cross-check each IP address against active resources:
Check EC2 instances or Elastic Load Balancers for active IPs.
For any IP addresses not associated with live resources, delete or update the corresponding DNS records in Route 53.
If needed, create new records that point to active resources.
Using AWS CLI:
To list Route 53 records, run:
aws route53 list-resource-record-sets --hosted-zone-id <hosted-zone-id>
Extract the A or AAAA records from the output and extract the IP addresses.
For each IP address, check if it is associated with an EC2 instance or Elastic IP by running:
aws ec2 describe-instances --filters "Name=private-ip-address,Values=<ip-address>"
If the IP is not associated with any active resource, delete the A record using:
aws route53 change-resource-record-sets --hosted-zone-id <hosted-zone-id> --change-batch file://delete-record.json
Backout Plan:
If removing or updating Route 53 records causes issues (e.g., misconfiguring DNS routing), follow these steps:
Identify the incorrect or removed DNS record.
If a record was mistakenly deleted or updated, restore it using the original IP address.
Run the following to add a record back:
aws route53 change-resource-record-sets --hosted-zone-id <hosted-zone-id> --change-batch file://add-record.json
Verify that the DNS record now points to the correct IP address and that services are routing correctly.
Note:
Monitoring: Consider using CloudWatch to monitor Route 53 logs and set up alarms for when unexpected changes occur to DNS records, ensuring that dangling IPs are detected early.
Automation: If you have a large number of DNS records to manage, consider automating this process with Lambda functions or using AWS Config to ensure that Route 53 records always point to valid resources.