Introducing Subnet-Watcher: Observability for your AWS Subnets

Are you tired of manually checking your AWS subnets to ensure they’re not approaching free remaining ip limit ? Look no further than Subnet-Watcher, an open-source tool I’ve developed at

Subnet-Watcher allows you to automatically check your subnets for a variety of metrics, such as whether they have the correct number of available IP addresses, number of detached ENIs. It also allows you to take action if any of these conditions are not met, such as sending an email notification and automatically record a CloudWatch Metric.

Available Metrics

  1. AvailableIpAddressCount - Number of IP Addresses available
  2. TotalIpAddressCount - Quantity of Total IP Addresses in subnet (based on CIDR size minus the 5 AWS reserved Ips)
  3. AvailableIpAddressPercent - Percentage of available IP Addresses
  4. AvailableNetworkInterface - Number of Elastic Network Interfaces Available (ENI) in VPC (with status = available)

Metric sample

CW Metrics Graph Count

One of the key features of Subnet-Watcher is its flexibility. It can be configured to check any number of subnets (Private and Public) and can be easily integrated into your existing infrastructure.

In addition, Subnet-Watcher is written in Python and uses the boto3 library for interfacing with the AWS API, making it easy to understand and customize for your specific needs.

With Subnet-Watcher, you can have peace of mind knowing that your subnets are in the desired state and that any issues proactively identified.

Try it out for yourself by visiting the project’s GitHub page.

That’s all folks!