AWS Exporting DynamoDB Name to Python - amazon-web-services

Question

I’m trying to make a DynamoDB table, without having a name property in the .yml file so that it’s name by cloud formation, and export it’s name to python for access can I do that if so how?
My current idea is to to export the name as a ssm parameter but I’m not sure how.

Answer 1

You can tag it in the cloudformation template and get resources by tag in boto.
import boto3
client = boto3.client('rds')
custom_filter = [{
'Name':'tag:Owner',
'Values': ['user#example.com']}]
response = client.describe_instances(Filters=custom_filter)
(This code is mostly copied from https://stackoverflow.com/a/48073016/10553976)
And this would correspond to tagging instances with the following:
Tags:
-
Key: "Owner"
Value: "user#example.com"
Important: if you want to apply the tags to something other than the instances you would need to use a different method from the describe methods in the rds client.

Answer 2

I assume your question is related to AWS CloudFormation, because you mention .yml file.
You can report the name in the output section of your cloudformation template, if your python function is declared in another template. You can then use the describe-stack API or CLI to fetch the value from the output.
See :
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/outputs-section-structure.html and https://docs.aws.amazon.com/cli/latest/reference/cloudformation/describe-stacks.html
If your python function is declared in the same template, you can just refer to your logical resource to get the name (as per https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-dynamodb-table.html)
For example,
The section that creates the table
MyTable:
Type: AWS::DynamoDB::Table
Description: your decsriptions
Properties:
... your properties ...
The section that refers to it (here is an example with AWS::AppSync::DataSource but it applies to any type of resources
MyTableDataSource:
Type: AWS::AppSync::DataSource
Properties:
...
DynamoDBConfig:
TableName:
Ref: MyTable
AwsRegion:
Fn::Sub: ${AWS::Region}
or to get the table ARN in a IAM Policy
Policies:
- PolicyName: mypolicy
PolicyDocument:
Version: 2012-10-17
Statement:
- Effect: Allow
Action:
- dynamodb:GetItem
- dynamodb:PutItem
- dynamodb:DeleteItem
- dynamodb:UpdateItem
- dynamodb:Query
- dynamodb:Scan
Resource:
- Fn::Join:
- ''
- - Fn::GetAtt:
- MyTable
- Arn
- '*'

Answer 3

According to your reply to my comment, you wish to add the DynamoDB table into the yml file. If the table and the lambda are in the same .yml, then you can simply do !Ref YourTable, inside the Lambda Environment variables.
Something like this:
YourLambda:
Type: AWS::Serverless::Function
Properties:
Environment:
Variables:
YourTableName: !Ref YourTable
You will also need to add a policy attached to the Lambda, under Properties -> Policies, and you can reference the table name there the same way.
However, if you wish to reference the name without moving the DynamoDB instance inside the .yml file, then you have to make it a static reference by making an entry in Parameter Store, and then referencing it like so (making sure your CFN has access to ssm:getParameter):
YourLambda:
Type: AWS::Serverless::Function
Properties:
Environment:
Variables:
YourTableName: '{{resolve:ssm:/PATH/TO/TABLENAME:1}}'

Answer 4

Here’s how I ended up doing it:
Python:
ssm = boto3.client('ssm')
resp = dict(ssm.get_parameter(Name='TableName', WithDecryption=False))
tableName = str(json.loads(json.dumps(resp['Parameter'],default=str))['Value'])
This is my cloudformation yaml file:
Resources:
DynamoTable:
Type: "AWS::DynamoDB::Table"
Properties:
AttributeDefinitions:
- AttributeName: A_Key
AttributeType: "S"
- AttributeName: Serial
AttributeType: "S"
KeySchema:
- AttributeName: A_Key
KeyType: HASH
- AttributeName: Serial
KeyType: RANGE
DynamoTableParameter:
Type: "AWS::SSM::Parameter”
Properties:
Name: "TableName”
Type: String
Value: !Ref DynamoTable