Automating network interface related configurations on red hat ami-7.5 - amazon-web-services

Question

I have an ENI created, and I need to attach it as a secondary ENI to my EC2 instance dynamically using cloud formation. As I am using red hat AMI, I have to go ahead and manually configure RHEL which includes steps as mentioned in below post.
Manually Configuring secondary Elastic network interface on Red hat ami- 7.5
Can someone please tell me how to automate all of this using cloud formation. Is there a way to do all of it using user data in a cloud formation template? Also, I need to make sure that the configurations remain even if I reboot my ec2 instance (currently the configurations get deleted after reboot.)

Answer 1

Though it's not complete automation but you can do below to make sure that the ENI comes up after every reboot of your ec2 instance (only for RHEL instances). If anyone has any better suggestion, kindly share.
vi /etc/systemd/system/create.service
Add below content
[Unit]
Description=XYZ
After=network.target
[Service]
ExecStart=/usr/local/bin/my.sh
[Install]
WantedBy=multi-user.target
Change permissions and enable the service
chmod a+x /etc/systemd/system/create.service
systemctl enable /etc/systemd/system/create.service
Below shell script does the configuration on rhel for ENI
vi /usr/local/bin/my.sh
add below content
#!/bin/bash
my_eth1=`curl http://169.254.169.254/latest/meta-data/network/interfaces/macs/0e:3f:96:77:bb:f8/local-ipv4s/`
echo "this is the value--" $my_eth1 "hoo"
GATEWAY=`ip route | awk '/default/ { print $3 }'`
printf "NETWORKING=yes\nNOZEROCONF=yes\nGATEWAYDEV=eth0\n" >/etc/sysconfig/network
printf "\nBOOTPROTO=dhcp\nDEVICE=eth1\nONBOOT=yes\nTYPE=Ethernet\nUSERCTL=no\n" >/etc/sysconfig/network-scripts/ifcfg-eth1
ifup eth1
ip route add default via $GATEWAY dev eth1 tab 2
ip rule add from $my_eth1/32 tab 2 priority 600
Start the service
systemctl start create.service
You can check if the script ran fine or not by --
journalctl -u create.service -b

Answer 2

Still need to figure out the joining of the secondary ENI from Linux, but this was the Python script I wrote to have the instance find the corresponding ENI and attach it to itself. Basically the script works by taking a predefined naming tag for both the ENI and Instance, then joins the two together.
Pre-reqs for setting this up are:
IAM role on the instance to allow access to S3 bucket where script is stored
Install pip and the AWS CLI in the user data section
curl -O https://bootstrap.pypa.io/get-pip.py
python get-pip.py
pip install awscli --upgrade
aws configure set default.region YOUR_REGION_HERE
pip install boto3
sleep 180
Note on sleep 180 command: I have my ENI swap out on instance in an autoscaling group. This allows an extra 3 min for the other instance to shut down and drop the ENI, so the new one can pick it up. May or may not be necessary for your use case.
AWS CLI command in user data to download the file onto the instance (example below)
aws s3api get-object --bucket YOURBUCKETNAME --key NAMEOFOBJECT.py /home/ec2-user/NAMEOFOBJECT.py
# coding: utf-8
import boto3
import sys
import time
client = boto3.client('ec2')
# Get the ENI ID
eni = client.describe_network_interfaces(
Filters=[
{
'Name': 'tag:Name',
'Values': ['Put the name of your ENI tag here']
},
]
)
eni_id = eni['NetworkInterfaces'][0]['NetworkInterfaceId']
# Get ENI status
eni_status = eni['NetworkInterfaces'][0]['Status']
print('Current Status: {}\n'.format(eni_status))
# Detach if in use
if eni_status == 'in-use':
eni_attach_id = eni['NetworkInterfaces'][0]['Attachment']['AttachmentId']
eni_detach = client.detach_network_interface(
AttachmentId=eni_attach_id,
DryRun=False,
Force=False
)
print(eni_detach)
# Wait until ENI is available
print('start\n-----')
while eni_status != 'available':
print('checking...')
eni_state = client.describe_network_interfaces(
Filters=[
{
'Name': 'tag:Name',
'Values': ['Put the name of your ENI tag here']
},
]
)
eni_status = eni_state['NetworkInterfaces'][0]['Status']
print('ENI is currently: ' + eni_status + '\n')
if eni_status != 'available':
time.sleep(10)
print('end')
# Get the instance ID
instance = client.describe_instances(
Filters=[
{
'Name': 'tag:Name',
'Values': ['Put the tag name of your instance here']
},
{
'Name': 'instance-state-name',
'Values': ['running']
}
]
)
instance_id = instance['Reservations'][0]['Instances'][0]['InstanceId']
# Attach the ENI
response = client.attach_network_interface(
DeviceIndex=1,
DryRun=False,
InstanceId=instance_id,
NetworkInterfaceId=eni_id
)