Question 95549 in Amazon Web Sevices Question posted in
The official Amazon Web Services documentation can be found here.

Grab Public IP Of a New Running Instance and send it via SNS – Amazon web services

So, I have this code, and I will love to grab the public IP address of the new windows instance that will be created when I adjust the desired capacity.
The launch template assigns an automatic tag name when I adjust the desired_capacity. I want to be able to grab the public IP address of that tag name.

import boto3

session = boto3.session.Session()
client = session.client('autoscaling')


def set_desired_capacity(asg_name, desired_capacity):
    response = client.set_desired_capacity(
        AutoScalingGroupName=asg_name,
        DesiredCapacity=desired_capacity,
    )
    return response


def lambda_handler(event, context):
    asg_name = "test"
    desired_capacity = 1
    return set_desired_capacity(asg_name, desired_capacity)


if __name__ == '__main__':
    print(lambda_handler("", ""))

I took a look at the EC2 client documentation, and I wasn’t sure what to use. I just need help modifying my code

Tags:

2

Answers


  1. 0

    If you know the tag that you are assigning in the autoscaling group, then you can just use a describe_instances method. The Boto3 docs have an example with filtering. Something like this should work, replacing TAG, VALUE, and TOPICARN with the appropriate values.

    import boto3

ec2_client = boto3.client('ec2', 'us-west-2')
sns_client = boto3.client('sns', 'us-west-2')

response = ec2_client.describe_instances(
Filters=[
    {
        'Name': 'tag:TAG',
        'Values': [
            'VALUE'
        ]
    }
]
)

for reservation in response["Reservations"]:
    for instance in reservation["Instances"]:
        ip = instance["PublicIpAddress"]
        sns_publish = sns_client.publish(
            TopicArn='TOPICARN',
            Message=ip,
        )
        print(sns_publish)
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  2. 0

    Objective:

    • After an EC2 instance starts
    • Obtain the IP address
    • Send a message via Amazon SNS

    It can take some time for a Public IP address to be assigned to an Amazon EC2 instance. Rather than continually calling DescribeInstances(), it would be easier to Run commands on your Linux instance at launch – Amazon Elastic Compute Cloud via a User Data script.

    The script could:

    IP=$(curl 169.254.169.254/latest/meta-data/public-ipv4)
    • Send a message to an Amazon SNS topic with:
    aws sns publish --topic-arn xxx  --message $IP

    If you also want the message to include a name from a tag associated with the instance, the script will need to call aws ec2 describe-instances with its own Instance ID (which can be obtained via the Instance Metadata) and then extra the name from the tags returned.

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