Things I keep Forgetting¶
Estimated time to read: 2 minutes
Public cloud instance metadata¶
Sometimes, particularly when testing or learning, it can be helpful to have data about a virtual machine that you're running. The cloud providers make this information via an Instance Metadata service. That means from within your VM you can query the service to find information such as the hostname, VM version, public IP address, and many more attributes. See the following links for specifics of each provider.
Accessing the data might be slightly different between each cloud however typically you can query the service via http://169.254.169.254.
The 169.254.0.0/16 range
If you've ever had networking issues with your PC where DHCP wasn't responding you might have seen an address assigned from the 169.254.0.0/16 range. This is a non-routable address and is used for dynamic configuration of IPv4 link-local addresses. You can find all the use cases in the following RFC
Here's a script to gather some AWS EC2 instance metadata, which could also be hosted behind a webserver.
display-instance-metadata.sh
This would run on the EC2 instance itself
TOKEN=$(curl --request PUT "http://169.254.169.254/latest/api/token" --header "X-aws-ec2-metadata-token-ttl-seconds: 3600")
instanceID=$(curl -s http://169.254.169.254/latest/meta-data/instance-id --header "X-aws-ec2-metadata-token: $TOKEN")
instanceAZ=$(curl -s http://169.254.169.254/latest/meta-data/placement/availability-zone --header "X-aws-ec2-metadata-token: $TOKEN")
hostname=$(curl -s http://169.254.169.254/latest/meta-data/local-hostname --header "X-aws-ec2-metadata-token: $TOKEN")
privateIPv4=$(curl -s http://169.254.169.254/latest/meta-data/local-ipv4 --header "X-aws-ec2-metadata-token: $TOKEN")
echo "Instance ID: $instanceID"
echo "AWS Availability Zone: $instanceAZ"
echo "Hostname: $hostname"
echo "Private IPv4 Address: $privateIPv4"