Creating Unique Hostnames for EC2 Instances in Elastic Beanstalk

While monitoring my Elastic Beanstalk application in Datadog, I noticed only one EC2 instance appeared in the Infrastructure view, despite having a fleet of multiple instances. This happens because Datadog defaults to using hostnames as unique identifiers, and Elastic Beanstalk instances typically share the same default hostname.

To fix this, we’ll set unique hostnames using EC2’s instance ID via Elastic Beanstalk’s prebuild hooks:

Here’s the script I added at .platform/hooks/prebuild/01_set_hostname.sh:

#!/bin/bash
INSTANCE_ID=$(curl -s http://169.254.169.254/latest/meta-data/instance-id)
sudo hostnamectl set-hostname "www.example.com-${INSTANCE_ID}"

How It Works

• The script runs during the prebuild phase on each EC2 instance
• It fetches the instance’s unique ID using AWS’s metadata service (available at 169.254.169.254)
• It sets a hostname with the instance ID appended
• Result: Each instance gets a unique hostname like www.example.com-i-1234567890abcdef0

Now Datadog can properly distinguish between different instances in the cluster, making monitoring and debugging much easier.

Note:

• This solution works for Linux-based Elastic Beanstalk environments
• Ensure the script has executable permissions (chmod +x)
• The hostname change persists across instance reboots
• The metadata service (169.254.169.254) is only accessible from within the EC2 instance