Does an AWS VPC Instance Retain Its Private IP Address After Stopping and Restarting?

When it comes to managing resources within the Amazon Virtual Private Cloud (VPC), one of the common questions pertains to the retention of private IP addresses. Specifically, users often want to know if an instance retains its private IP address when it is stopped and restarted.

Understanding Private IPs in AWS VPC

AWS VPC simplifies network configuration by allowing users to manage virtual networks and assign private IP addresses to instances. These private IP addresses are unique within the subnet and do not require public routing or internet access. However, as with many resources, there can be nuances to their behavior, especially when instances are stopped and restarted.

Do Instances Retain Their Private IPs?

The answer to this question is generally yes, provided the instance is stopped and not terminated. When you stop an instance, the state of the underlying operating system and associated resources is preserved, including the private IP address. Upon restart, the instance resumes its operation with the same private IP address, allowing for a seamless continuation of the service without the need for reconfiguration.

However, it's important to note that if you terminate the instance, the private IP address becomes released and is no longer affiliated with any active resources. In such a scenario, the private IP address is available to be reassigned to other instances within the same subnet.

Provisioning Elastic IPs (EIPs)

If you need to retain an IP address indefinitely, you should provision an Elastic IP (EIP) prior to starting the instance. An EIP is a public IP address that remains associated with your account until you choose to release it. This is particularly useful if you require a publicly accessible IP address for services that need to be permanently reachable, such as web servers or load balancers.

Here are the steps to assign an EIP to an instance:

Create an EIP in your account. Select the instance you want to assign the EIP to. Assign the EIP to the instance.

Assigning an EIP ensures that the instance retains a stable public IP address, even if the instance is stopped and restarted multiple times over a long period.

Stopping and Restarting Your Instance

For more detailed information on stopping and starting your instance, refer to the official AWS documentation:

Stop and Start Your Instance

This documentation provides step-by-step instructions, best practices, and considerations when managing the lifecycle of your EC2 instances.

Conclusion

In summary, AWS VPC instances do retain their private IP addresses after stopping and restarting, provided they were not terminated in the process. For maintaining long-term availability, consider provisioning an Elastic IP to ensure a public IP address remains associated with your instance, even during extended periods of inactivity.

Managing network configurations in AWS VPC effectively requires a clear understanding of these nuances. By leveraging the appropriate resources and best practices, you can ensure the reliability and availability of your applications and services.