Merge pull request #167 from CloudBytes-Academy/article

ART: dependency

content/aws/50007000-cdk-how-to-import-output.md

@@ -24,9 +24,7 @@ We need to use the `Fn.import_value` function to import the value of an Output.
 Let's first create the S3 bucket stack from the previous article. Create a new file called `cdk_app/s3_stack.py` and add the following code to it:
 
 ```python
-# cdk_app/s3_stack.py
-
-# cdk_app/s3_stack.py
+# filename: cdk_app/s3_stack.py
 
 from aws_cdk import (
     Stack,
@@ -87,7 +85,6 @@ class LambdaStack(Stack):
             code=_lambda.Code.from_asset("./"), # 👈🏽 Use the current directory as the source
             handler="index.main", # 👈🏽 Filename is index.py and the function is called main
         )
-
 ```
 
 In the above example, we imported the S3 bucket ARN using the `Fn.import_value` method. We then used the `from_bucket_arn` method to create a reference to the S3 bucket.

content/aws/50008000-cdk-inter-dependency-stack.md

@@ -0,0 +1,107 @@
+Title: Managing dependency between stacks in CDK
+Date: 2023-10-28
+Category: AWS Academy
+Series: AWS CDK
+series_index: 10
+Tags: aws, cdk, python
+Author: Rehan Haider
+Summary: How to specify dependency between stacks in CDK
+Keywords: AWS, cdk, python, dependency, stack
+
+
+Managing infrastructure means dealing with interconnected resources. In the AWS Cloud Development Kit (CDK), this often translates to specifying dependencies between different stacks. This post will guide you on how to define and manage these dependencies effectively within the CDK.
+
+
+## Why Specify Dependencies?
+
+The main use of specifying dependencies is to ensure that resources are deployed in the correct order. There are three main reasons why you would want to specify dependencies. For example, a Lambda function depends on an S3 bucket. The Lambda function needs to be deployed after the S3 bucket is created. This is because the Lambda function needs to access the S3 bucket. If the Lambda function is deployed before the S3 bucket, it will fail to access the S3 bucket.
+
+Another reason is to ensure that resources are deleted in the correct order. For example, if you delete the S3 bucket before the Lambda function, the Lambda function will fail to access the S3 bucket. This is because the S3 bucket no longer exists.
+
+## How to Specify Dependencies?
+
+There are two ways to specify dependencies in CDK. The first way is to use the `add_dependency` method. The second way is to use the `depends_on` property.
+
+### 1. Using the `add_dependency` Method
+
+Taking the code example in previous post that talks about [how to import stack outputs]({filename}50007000-cdk-how-to-import-output.md), let's create a stack that creates an S3 bucket and exports its ARN as an Output.
+
+You can use the `add_dependency` method to specify this dependency.
+
+```python
+import aws_cdk as cdk
+
+from cdk_app.s3_stack import S3Stack
+from cdk_app.lambda_stack import LambdaStack
+
+app = cdk.App()
+
+# LambdaStack depends on S3Stack
+
+s3_stack = S3Stack(app, "S3Stack")
+lambda_stack = LambdaStack(app, "LambdaStack")
+
+# 👇🏽 Add the dependency to ensure S3Stack is deployed first
+lambda_stack.add_dependency(s3_stack)
+
+app.synth()
+```
+
+### 2. Using the `depends_on` Property
+
+This is typically used if there a stack depends on more than one stack. For example, if you have a stack that contains a Lambda function that accesses an S3 bucket and a DynamoDB table, you can use the `depends_on` property to specify the dependencies.
+
+You will need to specify the dependencies as a list of stacks.
+
+```python
+import aws_cdk as cdk
+
+from cdk_app.s3_stack import S3Stack
+from cdk_app.lambda_stack import LambdaStack
+from cdk_app.dynamodb_stack import DynamoDBStack
+
+app = cdk.App()
+
+# LambdaStack depends on S3Stack
+
+s3_stack = S3Stack(app, "S3Stack")
+dynanodb_stack = DynamoDBStack(app, "DynamoDBStack")
+
+# 👇🏽 Specify that the stack depends on both s3_stack and dynamodb_stack
+lambda_stack = LambdaStack(app, "LambdaStack", depends_on=[s3_stack, dynamodb_stack])
+
+app.synth()
+```
+
+You can use the below for the dynamodb_stack.py file:
+
+```python
+# filename: cdk_app/dynamodb_stack.py
+
+from aws_cdk import (
+    Stack,
+    aws_dynamodb as ddb,
+    RemovalPolicy,
+)
+from constructs import Construct
+
+class DynamoDBStack(Stack):
+    TABLE_ID = "MyDynamoDBTable"
+
+    def __init__(self, scope: Construct, construct_id: str, **kwargs) -> None:
+        super().__init__(scope, construct_id, **kwargs)
+
+        myTable = ddb.Table(
+            self,
+            self.TABLE_ID,
+            partition_key={"name": "id", "type": ddb.AttributeType.STRING},
+            removal_policy=RemovalPolicy.DESTROY,
+        )
+```
+
+## Limitations of CDK Dependencies
+
+There are a few limitations of CDK dependencies that you should be aware of.
+
+1. **Circular Dependencies**: Be cautious to avoid circular dependencies where Stack A depends on Stack B and vice versa. This will result in an error.
+2. **Cross-Region Dependencies**: CDK doesn't support specifying dependencies across stacks in different AWS regions. For such scenarios, consider other synchronization methods or manually coordinating deployments.