Create AMI image as part of a cloudformation stack

Question

I want to create an EC2 cloudformation stack which basically can be described in the following steps:

1.- Launch instance

2.- Provision the instance

3.- Stop the instance and create an AMI image out of it

4.- Create an autoscaling group with the created AMI image as source to launch new instances.

Basically I can do 1 and 2 in one cloudformation template and 4 in a second template. What I don't seem able to do is to create an AMI image from an instance inside a cloudformation template, which basically generates the problem of having to manually remove the AMI if I want to remove the stack.

That being said, my questions are:

1.- Is there a way to create an AMI image from an instance INSIDE the cloudformation template?

2.- If the answer to 1 is no, is there a way to add an AMI image (or any other resource for that matter) to make it part of a completed stack?

EDIT:

Just to clarify, I've already solved the problem of creating the AMI and using it in a cloudformation template, I just can't create the AMI INSIDE the cloudformation template or add it somehow to the created stack.

As I commented on Rico's answer, what I do now is use an ansible playbook which basically has 3 steps:

1.- Create a base instance with a cloudformation template

2.- Create, using ansible, an AMI of the instance created on step 1

3.- Create the rest of the stack (ELB, autoscaling groups, etc) with a second cloudformation template that updates the one created on step 1, and that uses the AMI created on step 2 to launch instances.

This is how I manage it now, but I wanted to know if there's any way to create an AMI INSIDE a cloudformation template or if it's possible to add the created AMI to the stack (something like telling the stack, "Hey, this belongs to you as well, so handle it").

Answer 1

Yes, you can create an AMI from an EC2 instance within a CloudFormation template by implementing a Custom Resource that calls the CreateImage API on create (and calls the DeregisterImage and DeleteSnapshot APIs on delete).

Since AMIs can sometimes take a long time to create, a Lambda-backed Custom Resource will need to re-invoke itself if the wait has not completed before the Lambda function times out.

Here's a complete example:

Description: Create an AMI from an EC2 instance.
Parameters:
  ImageId:
    Description: Image ID for base EC2 instance.
    Type: AWS::EC2::Image::Id
    # amzn-ami-hvm-2016.09.1.20161221-x86_64-gp2
    Default: ami-9be6f38c
  InstanceType:
    Description: Instance type to launch EC2 instances.
    Type: String
    Default: m3.medium
    AllowedValues: [ m3.medium, m3.large, m3.xlarge, m3.2xlarge ]
Resources:
  # Completes when the instance is fully provisioned and ready for AMI creation.
  AMICreate:
    Type: AWS::CloudFormation::WaitCondition
    CreationPolicy:
      ResourceSignal:
        Timeout: PT10M
  Instance:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: !Ref ImageId
      InstanceType: !Ref InstanceType
      UserData:
        "Fn::Base64": !Sub |
          #!/bin/bash -x
          yum -y install mysql # provisioning example
          /opt/aws/bin/cfn-signal \
            -e $? \
            --stack ${AWS::StackName} \
            --region ${AWS::Region} \
            --resource AMICreate
          shutdown -h now
  AMI:
    Type: Custom::AMI
    DependsOn: AMICreate
    Properties:
      ServiceToken: !GetAtt AMIFunction.Arn
      InstanceId: !Ref Instance
  AMIFunction:
    Type: AWS::Lambda::Function
    Properties:
      Handler: index.handler
      Role: !GetAtt LambdaExecutionRole.Arn
      Code:
        ZipFile: !Sub |
          var response = require('cfn-response');
          var AWS = require('aws-sdk');
          exports.handler = function(event, context) {
            console.log("Request received:\n", JSON.stringify(event));
            var physicalId = event.PhysicalResourceId;
            function success(data) {
              return response.send(event, context, response.SUCCESS, data, physicalId);
            }
            function failed(e) {
              return response.send(event, context, response.FAILED, e, physicalId);
            }
            // Call ec2.waitFor, continuing if not finished before Lambda function timeout.
            function wait(waiter) {
              console.log("Waiting: ", JSON.stringify(waiter));
              event.waiter = waiter;
              event.PhysicalResourceId = physicalId;
              var request = ec2.waitFor(waiter.state, waiter.params);
              setTimeout(()=>{
                request.abort();
                console.log("Timeout reached, continuing function. Params:\n", JSON.stringify(event));
                var lambda = new AWS.Lambda();
                lambda.invoke({
                  FunctionName: context.invokedFunctionArn,
                  InvocationType: 'Event',
                  Payload: JSON.stringify(event)
                }).promise().then((data)=>context.done()).catch((err)=>context.fail(err));
              }, context.getRemainingTimeInMillis() - 5000);
              return request.promise().catch((err)=>
                (err.code == 'RequestAbortedError') ?
                  new Promise(()=>context.done()) :
                  Promise.reject(err)
              );
            }
            var ec2 = new AWS.EC2(),
                instanceId = event.ResourceProperties.InstanceId;
            if (event.waiter) {
              wait(event.waiter).then((data)=>success({})).catch((err)=>failed(err));
            } else if (event.RequestType == 'Create' || event.RequestType == 'Update') {
              if (!instanceId) { failed('InstanceID required'); }
              ec2.waitFor('instanceStopped', {InstanceIds: [instanceId]}).promise()
              .then((data)=>
                ec2.createImage({
                  InstanceId: instanceId,
                  Name: event.RequestId
                }).promise()
              ).then((data)=>
                wait({
                  state: 'imageAvailable',
                  params: {ImageIds: [physicalId = data.ImageId]}
                })
              ).then((data)=>success({})).catch((err)=>failed(err));
            } else if (event.RequestType == 'Delete') {
              if (physicalId.indexOf('ami-') !== 0) { return success({});}
              ec2.describeImages({ImageIds: [physicalId]}).promise()
              .then((data)=>
                (data.Images.length == 0) ? success({}) :
                ec2.deregisterImage({ImageId: physicalId}).promise()
              ).then((data)=>
                ec2.describeSnapshots({Filters: [{
                  Name: 'description',
                  Values: ["*" + physicalId + "*"]
                }]}).promise()
              ).then((data)=>
                (data.Snapshots.length === 0) ? success({}) :
                ec2.deleteSnapshot({SnapshotId: data.Snapshots[0].SnapshotId}).promise()
              ).then((data)=>success({})).catch((err)=>failed(err));
            }
          };
      Runtime: nodejs4.3
      Timeout: 300
  LambdaExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Principal: {Service: [lambda.amazonaws.com]}
          Action: ['sts:AssumeRole']
      Path: /
      ManagedPolicyArns:
      - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
      - arn:aws:iam::aws:policy/service-role/AWSLambdaRole
      Policies:
      - PolicyName: EC2Policy
        PolicyDocument:
          Version: '2012-10-17'
          Statement:
            - Effect: Allow
              Action:
              - 'ec2:DescribeInstances'
              - 'ec2:DescribeImages'
              - 'ec2:CreateImage'
              - 'ec2:DeregisterImage'
              - 'ec2:DescribeSnapshots'
              - 'ec2:DeleteSnapshot'
              Resource: ['*']
Outputs:
  AMI:
    Value: !Ref AMI