AWS- Does modyfing lambda update the CloudFormation Stack instantly? - amazon-web-services

Lets say I have a CloudFormation stack running, which creates and deploys an Lambda function. In the AWS Console, if I connect my Lambda function to an API in API Gateway, will my CloudFormation Template be updated immediately if the Lambda function successfully integrates with the API?

It's a one way traffic from Cloudformation to resources.
Meaning if you modify your Cloudformation template and update the stack then the resources that were created by Cloudformation get modified/updated. However the other way is not true. Meaning if you modify your resources the Cloudformation template does not get updated.
Moreover, as a good practice you should avoid modifying the resources directly because you may end up breaking the Cloudformation's update stack functionality for that that stack

Related

Deploy lambdas with single Cloudformation template

TLDR: Is there a way to -- using a single Cloudformation template -- deploy a lambda function with code in S3 or ECR?
Say I have two Lambda functions.
Function A has code in an S3 bucket and relies on a Lambda Layer
Function B is a containerized function with the image in an ECR instance
Here's my deployment setup for the two functions:
function-a/
s3-bucket.template // CFN Stack template for S3 bucket
lambda-function.template // CFN Stack template for lambda function
deploy.sh // Script that creates S3 bucket template,
builds/uploads code,
and creates lambda function stack
function-b/
ecr.template // CFN Stack template for ECR instance
lambda-function.template // CFN Stack template for lambda function
deploy.sh // Script that creates ECR,
builds/uploads docker image,
and creates lambda function stack
Results: 4 Cloudformation stacks, 1 S3 bucket, 1 ECR, 2 Lambda functions
I find this amount of configuration setup for these two functions needlessly complex.
I understand that buckets and registries need to exist. But I don't want to explicitly define/deploy/manage them using extra build steps.
What else I looked at: I checked AWS SAM -- but SAM also doesn't absolve me from managing the code deployment myself. I used AWS CDK which actually abstracts this away. But for certain reasons I don't want to use CDK here atm. I do not want to use the Serverless framework.
I'm disappointed that most of the examples from the documentation of Cloudformation and SAM just end up creating buckets and registries manually. This doesn't seem like a scalable way to handle it for many environments. This isn't Infrastructure-as-Code.
Is there a simpler way?
The S3 bucket and ECR would be reused for future functionality. So I think of it as two shared resources (S3 code bucket and ECR) and then two new resources (the new Lambda functions).
Most likely you'll have a stack of shared items, things are used by everything but don't structurally change that much. Then another stack of application functions, which will likely change more often. Separating these two different types of things is a good idea.

Rollbacking changes made by lambda in CloudFormation

Is there any way to rollback all the changes made by an AWS Lambda by using the SDK? E.g. the lambda created and launched by a CloudFormation template creates a bucket via the AWS SDK. In case something fails it would be great to have a 'stack rollback' for the same stack that deployed the lambda as well (and all the resources created by the lambda reverted as well).
Or alternatively: how can I 'remember' from my lambda which resources were created so that I can rollback them and delete them when the lambda is called afterwards with a 'Delete' event?
I'm assuming you mean custom resources, as that's the only way you can run scripts in cloudformation.
Custom resources have a property called pysicalReourceId. You can use it after your create event to provide info over the resource you've created. When updating or deleting the resource, the id is provided to the lambda event so you can use it. A guide can also be found here: https://advancedweb.hu/how-to-use-the-physicalresourceid-for-cloudformation-custom-resources/
If for some reason it's not possible to use the resource ID I'd use tagging. When creating, tag your resources and when deleting, fetch the resources based on their tag and delete them.

adding CloudWatch to a stack with CloudFormation

I am currently in charge of adding CloudWatch integration to an already made Cloud Formation stack.
We create the stacks through CLI, but at the moment we add CloudWatch manually afterwards.
What i need is to automatically activate CloudWatch for instances and monitor CPU, hdd and so on through the use of CloudFormation templates.
Thanks in advance!
My suggestion is that you don't add new CloudWatch items to the existing CloudFormation stack. Instead, create a CF template with the appropriate metrics and deploy from this template for each instance you want to monitor.
From there, I suggest you create an AWS Lambda function that will receive an Instance Id as input and will deploy a CloudFormation stack against the instance. You should enable CloudTrail on your account and create a Rule to match any RunInstances event on the account and trigger the Lambda function.
Keep in mind the default limit for CloudFormation stacks is 200. You might need to request an increase depending on your use case.

Same CloudFormation template to parameterize DeletionPolicy?

As a DevOps guy I wanted to use the same template to provision both Dev and Prod stacks... Where dev stacks should not have any DeletionPolicy but Prod stacks should utilize a DeletionPolicy
So, at first sight CFT gives an ok tooling for this but.... there is no possibility to parametrize S3 DeletionPolicy (that I've been able to locate at least)...
Here's some threads I dug up
https://forums.aws.amazon.com/message.jspa?messageID=560586
https://www.unixdaemon.net/cloud/cloudformation-annoyance-deletion-policy-parameters/
The suggested workaround from AWS was to make the whole resource conditional, which leads us duplicating the resource and create a „Deletable and „Undeletable versions of it and all the depending resources should handle that condition...
This seems wonky and bloated, is there a way to parameterize this or a better methodology to accomplish my end goal?
Doesn't seem like there's an option in CFT other than resource duplication.
What you can do is create a Lambda with a Python script that would setup the S3 deletion policy. That Lambda function can be triggered through SNS during CloudFormation stack creation. Here is described how this can be configured:
Is it possible to trigger a lambda on creation from CloudFormation template
But in your particular case I'd go with resource duplication in same CFT.

How to send SNS notification after cloud formation is completed?

Is it possible to send a SNS notification after the CFT completion in AWS ? Is there any way to get the progress of the launching CFT in AWS.
When create resources using a CF template there is an Advanced section of the Options menu. From there you can set Notification options using SNS and Topics.
When you start the CF process you can also view the status and importantly where the template might have failed.
You cannot specify notification ARNs via a CloudFormation template itself. You can specify them if you use the console to create the stack creation. But you cannot use the console to update the ARNs once the stack has been created. You can, however, use aws-cli to update the stack with notifications ARNs once it has been created, eg:
aws cloudformation update-stack --stack-name stack-name --use-previous-template --notification-arns "arn:aws:sns:us-east-1:${ACCOUNT_ID}:${TOPIC_NAME}"
Replace the variable ${VARIABLE} with the literal values from your account.
There's also knowledge center article from AWS where you can replace ROLLBACK_IN_PROGRESS statement with any other state of CloudFormation to get SNS Notification.
You can trick CloudFormation into sending SNS messages from inside the template:
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/template-custom-resources.html
Custom resources enable you to write custom provisioning logic in
templates that AWS CloudFormation runs anytime you create, update (if
you changed the custom resource), or delete stacks. For example, you
might want to include resources that aren't available as AWS
CloudFormation resource types. You can include those resources by
using custom resources. That way you can still manage all your related
resources in a single stack.
Use the AWS::CloudFormation::CustomResource or Custom::String resource
type to define custom resources in your templates. Custom resources
require one property: the service token, which specifies where AWS
CloudFormation sends requests to, such as an Amazon SNS topic.