如何获取未使用的Elastic IP及编写Shell脚本关联至新实例？

Hey there! Let's break down your request into two actionable parts: first, a direct AWS CLI command to find unused Elastic IPs, and second, a shell script that automates the full workflow—finding idle EIPs, spinning up a new instance, and linking them together.

1. Query Unused Elastic IPs with AWS CLI #

To get a list of EIPs that aren't associated with any EC2 instance, we can use aws ec2 describe-addresses with a filter targeting empty AssociationId values (this is how AWS marks unused EIPs).

Here's the command:

aws ec2 describe-addresses --filters "Name=association-id,Values=''" --query 'Addresses[*].[PublicIp,AllocationId]' --output table

What each part does: #

• --filters "Name=association-id,Values=''": Filters results to only include EIPs with no association (i.e., unused).
• --query 'Addresses[*].[PublicIp,AllocationId]': Narrows down the output to just the public IP and allocation ID (the two values you'll need for association later).
• --output table: Makes the results human-readable. Swap this for json or text if you need machine-parsable output.

2. Shell Script to Automate EIP Association with a New Instance #

This script will:

1. Check for any unused EIPs
2. If none exist, create a new EIP
3. Launch a new EC2 instance (you'll need to tweak the AMI ID and instance type for your region/needs)
4. Wait for the instance to be running
5. Associate the EIP (existing or new) with the instance

#!/bin/bash

# Query the first unused Elastic IP (returns AllocationId and PublicIp)
FREE_EIP=$(aws ec2 describe-addresses --filters "Name=association-id,Values=''" --query 'Addresses[0].[AllocationId,PublicIp]' --output text)

# Handle case where no unused EIPs exist
if [ -z "$FREE_EIP" ]; then
    echo "No unused Elastic IPs found. Creating a new one..."
    NEW_EIP=$(aws ec2 allocate-address --query '[AllocationId,PublicIp]' --output text)
    ALLOCATION_ID=$(echo "$NEW_EIP" | awk '{print $1}')
    PUBLIC_IP=$(echo "$NEW_EIP" | awk '{print $2}')
else
    ALLOCATION_ID=$(echo "$FREE_EIP" | awk '{print $1}')
    PUBLIC_IP=$(echo "$FREE_EIP" | awk '{print $2}')
    echo "Found unused Elastic IP: $PUBLIC_IP (Allocation ID: $ALLOCATION_ID)"
fi

# Launch a new EC2 instance (UPDATE THESE PARAMETERS FOR YOUR USE CASE!)
# Replace the AMI ID with one valid for your AWS region (e.g., Amazon Linux 2, Ubuntu, etc.)
INSTANCE_ID=$(aws ec2 run-instances \
    --image-id ami-0c55b159cbfafe1f0 \  # us-east-1 Amazon Linux 2 AMI—swap for your region!
    --instance-type t2.micro \
    --count 1 \
    --query 'Instances[0].InstanceId' \
    --output text)

echo "Created EC2 instance: $INSTANCE_ID"

# Wait for the instance to enter the running state (critical for successful association)
echo "Waiting for instance to start up..."
aws ec2 wait instance-running --instance-ids $INSTANCE_ID

# Associate the Elastic IP with the new instance
aws ec2 associate-address --instance-id $INSTANCE_ID --allocation-id $ALLOCATION_ID

echo "Successfully linked Elastic IP $PUBLIC_IP to instance $INSTANCE_ID"

Key Notes & Customizations: #

• AWS CLI Setup: Ensure your CLI is configured with valid credentials and the correct region (run aws configure to set this up).
• AMI ID: The example uses a us-east-1 Amazon Linux 2 AMI. Find the right AMI for your region via the AWS Console or aws ec2 describe-images.
• Instance Configuration: Add flags like --security-group-ids sg-xxxxxx or --subnet-id subnet-xxxxxx to customize the instance's network settings.
• IAM Permissions: Make sure your IAM user/role has these permissions: ec2:DescribeAddresses, ec2:AllocateAddress, ec2:RunInstances, ec2:AssociateAddress, and ec2:WaitInstanceRunning.
• Error Handling: For production use, add checks (e.g., if [ $? -ne 0 ]) to catch failures at each step and exit gracefully.

内容的提问来源于stack exchange，提问作者Tanjila