如何通过Python API及AWS API根据负载均衡器名称获取ARN

Hey Mike, let's break down your questions and clear up the confusion around getting your load balancer's ARN for that CloudWatch metric setup.

1. Retrieving ARN via Python Boto3 API #

The approach depends on the type of load balancer you're working with—here's how to handle both common types:

For Application/Network Load Balancers (ELBv2) #

These newer LB types return the ARN directly in the describe_load_balancers response. Use this code snippet to fetch it by name:

import boto3

def get_lb_arn(lb_name, region='us-east-1'):
    elbv2_client = boto3.client('elbv2', region_name=region)
    response = elbv2_client.describe_load_balancers(Names=[lb_name])
    
    if response['LoadBalancers']:
        return response['LoadBalancers'][0]['LoadBalancerArn']
    else:
        raise ValueError(f"Load balancer with name {lb_name} not found")

# Example usage
try:
    lb_arn = get_lb_arn('your-target-lb-name')
    print(f"Found LB ARN: {lb_arn}")
except ValueError as e:
    print(e)

For Classic Load Balancers #

Classic LBs don't return the ARN directly from the legacy elb client's describe_load_balancers call. Instead, you can construct it using your AWS account ID, region, and LB name (you can fetch your account ID via boto3 easily):

import boto3

def get_classic_lb_arn(lb_name, region='us-east-1'):
    sts_client = boto3.client('sts', region_name=region)
    account_id = sts_client.get_caller_identity()['Account']
    
    # Build the ARN using the standard classic LB format
    return f"arn:aws:elasticloadbalancing:{region}:{account_id}:loadbalancer/{lb_name}"

# Example usage
classic_lb_arn = get_classic_lb_arn('your-classic-lb-name')
print(f"Classic LB ARN: {classic_lb_arn}")

2. Can AWS API Return the Load Balancer ARN? #

Absolutely! The confusion about missing ARNs in your response is almost certainly tied to using the wrong API client for your LB type:

• Application/Network LBs: The ELBv2 API (elbv2.describe_load_balancers) explicitly includes the LoadBalancerArn field in every load balancer object in the response.
• Classic LBs: The legacy ELB API doesn't return the ARN directly, but it follows a predictable structure you can construct (as shown above).

If you were using the elb client for an Application/Network LB, that's why you didn't see the ARN—switch to the elbv2 client instead.

3. Quick Note for Your CloudWatch Metric Setup #

When adding the DDoSAttackBitsPerSecond metric to your AWS Dashboard, make sure you use the full ARN (not just the LB name) as the dimension. The code snippets above will give you the exact format CloudWatch expects, so you can plug that value directly into the dimension field without issues.

内容的提问来源于stack exchange，提问作者Mikey