add ami lookup custom resource

jenkins-ec2-agents.cfhighlander.rb

@@ -13,5 +13,6 @@
     ComponentParam 'Subnets', type: 'CommaDelimitedList'
   end
 
+  LambdaFunctions 'ami_finder_custom_resources'
 
 end

jenkins-ec2-agents.cfndsl.rb

@@ -40,18 +40,24 @@
     Tags agent_tags
   }
 
+  Resource(:LinuxAmiFinder) {
+    Type 'Custom::LinuxAmiFinder'
+    Property 'ServiceToken', FnGetAtt(:AmiFinderCR, :Arn)
+    Property 'Name', linux_ami
+  }
+
   SSM_Parameter(:LinuxAmiParameter) {
     Description "AMI Id for the Jenkins linux agent"
     Name FnSub("/ciinabox/${EnvironmentName}/agent/linux/ami")
     Property('Tier','Standard')
     Type 'String'
-    Value 'ami-replaceme'
+    Value Ref(:LinuxAmiFinder)
     Property('Tags',{
       Name: "#{external_parameters[:component_name]}-linux-ami",
       EnvironmentName: Ref(:EnvironmentName)
     })
   }
-  
+
   SSM_Parameter(:WindowsAmiParameter) {
     Description "AMI Id for the Jenkins linux agent"
     Name FnSub("/ciinabox/${EnvironmentName}/agent/windows/ami")

jenkins-ec2-agents.config.yaml

@@ -1,3 +1,5 @@
+linux_ami: 'Amzn2_Linux_Jenkins_Agent-*'
+
 iam_policies:
   sts:
     action:
@@ -27,4 +29,30 @@ iam_policies:
       - ssmmessages:CreateControlChannel
       - ssmmessages:CreateDataChannel
       - ssmmessages:OpenControlChannel
-      - ssmmessages:OpenDataChannel
+      - ssmmessages:OpenDataChannel
+
+ami_finder_custom_resources:
+  custom_policies:
+    ami:
+      action:
+        - ec2:DescribeImages
+      resource: '*'
+    lambda:
+      action:
+        - lambda:InvokeFunction
+      resource:
+        Fn::Sub: arn:aws:lambda:${AWS::Region}:${AWS::AccountId}:function:AmiFinderCR
+  roles:
+    AmiFinderResource:
+      policies_inline:
+        - cloudwatch-logs
+        - ami
+        - lambda
+  functions:
+    AmiFinderCR:
+      code: ami_finder/app.py
+      handler: app.handler
+      runtime: python3.8
+      timeout: 600
+      role: AmiFinderResource
+      package_cmd: 'pip install -r requirements.txt -t .'

lambdas/ami_finder/app.py

@@ -0,0 +1,41 @@
+import boto3
+from crhelper import CfnResource
+import logging
+import json
+
+logger = logging.getLogger(__name__)
+# Initialise the helper, all inputs are optional, this example shows the defaults
+helper = CfnResource(json_logging=False, log_level='DEBUG', boto_level='CRITICAL')
+
+@helper.create
+def create(event, context):
+    logger.info(f"Creating resource {event}")    
+    return get_latest_ami(event['ResourceProperties']['Name'])
+
+@helper.update
+def update(event, context):
+    logger.info(f"Updating resource {event}")
+    return get_latest_ami(event['ResourceProperties']['Name'])
+
+@helper.delete
+def delete(event, context):
+    logger.info(f"Deleting resource {event}")
+
+def get_latest_ami(name):
+    client = boto3.client('ec2')
+
+    filters = []
+    filters.append({'Name': 'name', 'Values': [name]})
+    response = client.describe_images(Filters=filters)
+
+    if not response['Images']:
+        return None
+
+    response['Images'].sort(key=lambda r: r['CreationDate'])
+    return response['Images'][-1]['ImageId']
+
+def handler(event, context):
+    helper(event, context)
+
+
+    'Amzn2_Linux_Jenkins_Agent-*'

lambdas/ami_finder/requirements.txt

@@ -0,0 +1 @@
+crhelper