Why is my static IP address not sticking on AWS EC2 after reboot, causing downtime?

Hey everyone,

Following up on a previous discussion about needing a stable IP for my new SaaS app, I decided to go with an Elastic IP on AWS EC2, thinking it would be the perfect set-and-forget solution for a dynamic IP problem. My goal was to ensure my application always had a consistent endpoint for users and external services.

However, I've run into a frustrating issue. My app is experiencing intermittent downtime because the static Public IP Address (Elastic IP) isn't consistently re-associating with my EC2 instance after reboots or instance stops/starts. I expected it to be a robust and persistent solution, but it frequently requires manual intervention to get things back online, which is far from ideal for a production environment.

Here's what I've tried so far to troubleshoot this:

• Allocated a new Elastic IP and associated it directly with my running EC2 instance. I made sure to confirm the association in the AWS console.
• Verified the association status in the AWS console multiple times, both before and after testing reboots.
• Performed several instance reboots and stop/start cycles to rigorously test the persistence of the Elastic IP.
• Attempted to disassociate and then manually re-associate the Elastic IP when it failed to re-attach automatically. This usually fixes it temporarily.
• Checked relevant Security Groups and Network ACLs, ensuring traffic is allowed on the necessary ports. While this seems unrelated to the IP association itself, I wanted to rule out any network-level blocks.

Despite these efforts, the problem persists. The static Public IP Address sometimes detaches or simply fails to automatically re-attach to the instance after a restart, leaving the instance completely inaccessible via its public IP until I manually intervene and fix it. This completely defeats the purpose of having a stable, persistent IP for my application.

I'm really scratching my head here and could use some expert advice. Specific questions I have are:

• Am I missing a fundamental step in ensuring Elastic IP persistence on EC2 after restarts? Is there some configuration detail beyond just associating it that I'm overlooking?
• Are there common configuration errors or best practices for ensuring a static Public IP Address remains bound through reboots that I should be aware of?
• Could this be an issue with the instance type (I'm using a t3.micro) or the AMI I'm using? Perhaps certain AMIs handle network interfaces differently?
• Are there any recommended automation scripts or AWS services (like Lambda functions or EventBridge rules) that can monitor and automatically re-associate EIPs if they detach unexpectedly?

Any insights or guidance would be hugely appreciated. Help a brother out please, this downtime is killing my early user experience!