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Here's what I have in AWS:
Everything works. However, when I need to make an update or change to the servers, I am currently manually creating a new AMI_B, creating a new LaunchConfig using AMI_B, updating the AutoScalingGroup to use the new LaunchConfig, increasing min number of instances to 4, waiting for them to become available, then decreasing the number back to 2 to kill off the old instances.
I'd really love to automate this process. Amazon gave me some links to CLI stuff, and I'm able to script the AMI creation, create the LaunchConfig, and update the AutoScalingGroup...but I don't see an easy way to script spinning up the new instances.
After some searching, I found some CloudFormation templates that look like they'd do what I want, but most do more, and it's a bit confusing to me.
Should I be exploring CloudFormation? Is there a simple guide I can follow to get started? Or should I stay with the scripting I have started?
PS - sorry if this is a repeated question. Things change frequently at AWS, so sometimes the older responses may not be the current best answers.
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Verify that you see the new launch template, and that it uses the new AMI. Choose Auto Scaling, and then choose Auto Scaling Groups. Verify that the Auto Scaling group uses the new launch template. Terminate one or more instances in your Auto Scaling group.
In the console, Open EC2 > Auto scaling groups > select group > switch to instance management tab. In case a scale-out event triggered for this auto-scaling group, it would keep the instance under Pending:Wait status.
Select the launch configuration and choose Actions, Copy launch configuration. This sets up a new launch configuration with the same options as the original, but with "Copy" added to the name. On the Copy Launch Configuration page, edit the configuration options as needed and choose Create launch configuration.
We strongly recommend that all Auto Scaling groups use launch templates to ensure full functionality for Amazon EC2 Auto Scaling and Amazon EC2. Updates the configuration for the specified Auto Scaling group. To update an Auto Scaling group, specify the name of the group and the property that you want to change.
You have a number of options to automate the process of updating the instances in an Auto Scaling Group to a new or updated Launch Configuration:
If you do want to use CloudFormation to manage updates to your Auto Scaling Group's instances, refer to the UpdatePolicy attribute of the AWS::AutoScaling::AutoScalingGroup Resource for documentation, and the "What are some recommended best practices for performing Auto Scaling group rolling updates?" page in the AWS Knowledge Center for more advice.
If you'd also like to script the creation/update of your AMI within a CloudFormation resource, see my answer to the question, "Create AMI image as part of a cloudformation stack".
Note, however, that CloudFormation is not a simple tool- it's a complex, relatively low-level service for orchestrating AWS resources, and migrating your existing scripts to it will likely take some time investment due to its steep learning curve.
If simplicity is most important, then I'd suggest you evaluate Elastic Beanstalk, which also supports both rolling and immutable updates during deployments, in a more fully managed, console-oriented, platform-as-a-service environment. Refer to my answer to the question, "What is the difference between Elastic Beanstalk and CloudFormation for a .NET project?" for further comparisons between CloudFormation and Elastic Beanstalk.
If you want a solution for updating instances in an auto-scaling group that you can plug into existing scripts, AWS CodeDeploy might be worth looking into. You install an agent on your instances, then trigger deployments through the API/CLI/Console and it manages deploying application updates to your fleet of instances. See Deploy an Application to an Auto Scaling Group Using AWS CodeDeploy for a complete tutorial. While CodeDeploy supports 'in-place' deployments and 'blue-green' deployments (see Working With Deployments for details), I think this service assumes an approach of swapping out S3-hosted application packages onto a static base AMI rather than replacing AMIs on each deployment. So it might not be the best fit for your AMI-swapping use case, but perhaps worth looking into anyway.
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You want a custom Termination policy on the Auto Scaling Group.
OldestLaunchConfiguration. Auto Scaling terminates instances that have the oldest launch configuration. This policy is useful when you're updating a group and phasing out the instances from a previous configuration.
To customize a termination policy using the console
Select the Auto Scaling group.
For Actions, choose Edit.
On the Details tab, locate Termination Policies. Choose one or more termination policies. If you choose multiple policies, list them in the order that you would like them to apply. If you use the Default policy, make it the last one in the list.
Choose Save.
On the CLI
aws autoscaling update-auto-scaling-group --auto-scaling-group-name my-asg --termination-policies "OldestLaunchConfiguration"
https://docs.aws.amazon.com/autoscaling/latest/userguide/as-instance-termination.html
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