Unable to Fetch the Details of Private EC2 Instance using Lambda Function

Hi,

1. Go to Lambda console.
2. Select the function that you want to use to connect to private instance.
3. Choose Configuration and then choose VPC.
4. Under VPC, click Edit.
5. Choose a VPC, subnets, and security groups.
6. Add at least two private subnets. Attach security groups and make sure that security groups allow required ports and protocols based on your requirement.
7. Choose Save.

Now the next thing is EC2. At EC2 instance side, make sure one of the security group attached the EC2 instance can receive traffic(Inbound rule) from the SG assigned to the Lambda function. Also, make sure SG assigned to the lambda function can make outbound calls to EC2( can usually be open to everything)

Make sure you add appropriate rules in the security group at both sides to allow traffic.

Please refer Configuring a Lambda function to access resources in a VPC

What about having Lambda run Systems Manager Run Command so that files are copied from S3, such as s3 cp?
Attach an IAM role to the EC2 with the AmazonSSMMManagedInstanceCore set in the IAM policy.
If the EC2 is located on a private subnet, configure it to communicate with Systems Manager using a NAT gateway or VPC endpoint.
Create a function to execute SSM RunCommand in Lambda.
Lambda is executed when a file is created in S3.
The following document is an example for Windows.
https://repost.aws/questions/QU3rKJmmtRQ_aFX61wa_VnJw/lambda%E3%81%8B%E3%82%89-ec-2-run-command%E3%82%92%E5%AE%9F%E8%A1%8C%E3%81%99%E3%82%8B%E6%96%B9%E6%B3%95%EF%BC%88-windows%EF%BC%89

In the case of Linux, the following code would do.
If this can be used successfully, there is no need to connect Lambda to the VPC.
https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/ssm/client/send_command.html

import boto3

ssm = boto3.client('ssm')

def lambda_handler(event, context):
    bucket = event['Records'][0]['s3']['bucket']['name']
    key = event['Records'][0]['s3']['object']['key']
    response = ssm.send_command(
        InstanceIds=['instance-id'],
        DocumentName='AWS-RunShellScript',
        Parameters={
            'commands': [
                f'aws s3 cp s3://{bucket}/{key} /path/file_name'
            ],
            'executionTimeout': ['3600'],
        }
    )

Please check your lambda configuration as mentioned in below link https://docs.aws.amazon.com/lambda/latest/dg/configuration-vpc.html