Pass variable in user data using boto3 while creating EC2 Instance

Question

I am creating EC2 instance and want to pass user data to attach a filesystem, but I don't know how to pass file system ID as a variable.

The file system ID will be passed using the API gateway. I have tried following but user data contains $aa not aa values.

aa='fs-ce99bd38'
user_data = """#!bin/bash
sudo yum -y install nfs-utils
sudo mount -t efs -o tls $aa:/ efs
"""

client = boto3.client('ec2', region_name=REGION)

def lambda_handler(event, context):

    instance = client.run_instances(
        ImageId=AMI,
        InstanceType=INSTANCE_TYPE,
        KeyName=KEY_NAME,
        UserData=user_data,
        MaxCount=min_max_add,
        MinCount=min_max_add
    )

In case to use aa environment variable you need to assign it which is outside the userdata block can you have it inside the userdata block? — Prashanna
– Prashanna, Commented Mar 8, 2021 at 9:53

Maurice · Accepted Answer · 2021-03-08 09:59:30Z

6

That's now how you insert a variable into a string :-)

If you have a reasonably modern Python version you can use f-strings like this:

aa='fs-ce99bd38'
user_data = f"""#!bin/bash
sudo yum -y install nfs-utils
sudo mount -t efs -o tls {aa}:/ efs
"""

Otherwise good old format will do the trick as well:

aa='fs-ce99bd38'
user_data = """#!bin/bash
sudo yum -y install nfs-utils
sudo mount -t efs -o tls {}:/ efs
""".format(aa)

Or the even older % operator

aa='fs-ce99bd38'
user_data = """#!bin/bash
sudo yum -y install nfs-utils
sudo mount -t efs -o tls %s:/ efs
""" % aa

answered Mar 8, 2021 at 9:59

Maurice

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