Cloudformation Attach instance to Auto scaling group - amazon-web-services

Question

In my CloudFormation file, I created an instance, a Launch Configuration and an Auto Scaling Group.
LogstashInstance:
Type: AWS::EC2::Instance
Properties:
IamInstanceProfile:
Ref: LogstashInstanceProfile
InstanceType: t2.micro
KeyName: chuongtest
ImageId: ami-0cd31be676780afa7
UserData:
SecurityGroupIds:
- Ref: LogstashSecurityGroup
SubnetId: subnet-0e5691582096fe1e6
Tags:
- Key: Name
Value: Logstash Instance
LogstashLaunchConfiguration:
Type: AWS::AutoScaling::LaunchConfiguration
Properties:
EbsOptimized: false
IamInstanceProfile:
Ref: LogstashInstanceProfile
ImageId: ami-0cd31be676780afa7
InstanceMonitoring: true
InstanceType: t2.micro
KeyName: chuongtest
LaunchConfigurationName: LogstashLaunchConfiguration
SecurityGroups:
- Ref: LogstashSecurityGroup
UserData:
LogstashAutoScalingGroup:
Type: AWS::AutoScaling::AutoScalingGroup
Properties:
AutoScalingGroupName: LogstashAutoScalingGroup
AvailabilityZones:
- ap-southeast-1b
DesiredCapacity: 1
LaunchConfigurationName:
Ref: LogstashLaunchConfiguration
MaxSize: 1
MinSize: 1
Tags:
- Key: Name
PropagateAtLaunch: "false"
Value: Logstash ASG
- Key: Instances
PropagateAtLaunch: "true"
Value: Logstash
My idea is to create an instance, attach it to the ASG and use the ASG to keep the work continue.
But this code will launch 2 instances.
The first instances has userdata different from the later instances so I can not delete the instance.
I have looked in the documentation but I can not find anything make sense. Is there a way to configure in the template, or the only way is scripting?

Answer 1

I have looked in the documentation but I can not find anything make sense. Is there a way to configure in the template, or the only way is scripting?
It does not make sense, because its not practical. ASG will be launching instances only from the associated AWS::AutoScaling::LaunchConfiguration. Thus, there is not much sense on "manually" attaching instances in your cause the the ASG. ASG will not re-launch it when it fails.
If the "manually" attached instances gets terminated for some reason, e.g. hardware failure, ASG will launch a replacement based on the launch configuration.
userdata different from the later instances
In this case the best would be to provide some condition in your UserData which would determine which version of your UserData to run.
Alternatively, just have two ASGs. One for the first instance, while the other group for the remaining instances.

Answer 2

Edit
Having discussed via the comments I would highly recommend the approach of using EFS as it is designed for the workload design you're doing.
In addition it is multi AZ vs the approach of rotating a single EBS volume as instances fail in an autoscaling group which would not persist should the AZ fail and potentially lead to loss of data.
Original
If that first instance is different from the rest you should be careful about adding it to the autoscaling group (as you want it to persist), especially in how it handles the replacement of instances.
Autoscaling groups are designed to scale similar instances that are generally immutable, so by having your host in this autoscaling group it will be treated as if it is one of the other hosts.
An Auto Scaling group contains a collection of Amazon EC2 instances that are treated as a logical grouping for the purposes of automatic scaling and management.
If you must add it to the autoscaling group here is the general approach:
Create a Custom Resource which involves a Lambda attaching the EC2 to the ASG using attach_instances
Add set_instance_protection to your instance to prevent it being replaced during a scale in event (or the instance failing)
Also ensure you set both the MinSize and DesiredCapacity to 0 to remove any extra instance that gets launched.
As I stated earlier you should not add this instance to the ASG if it can be avoided, tt will probably lead to confusion.