Dynamic environment variables for AWS Lambda using cloudformation template - amazon-web-services

Question

I have to use AWS lambda in various stack of my application, thus I have created a generic cloud-formation template to create a lambda function. This template can be included in another cloud-formation template for further use as a nested stack.
# Basics
AWSTemplateFormatVersion: '2010-09-09'
Description: AWS CloudFormation Template to create a lambda function for java 8 or nodejs
# Parameters
Parameters:
FunctionName:
Type: String
Description: Funciton Name
HandlerName:
Type: String
Description: Handler Name
FunctionCodeS3Bucket:
Type: String
Description: Name of s3 bucket where the function code is present
Default: my-deployment-bucket
FunctionCodeS3Key:
Type: String
Description: Function code present in s3 bucket
MemorySize:
Type: Number
Description: Memory size between 128 MB - 1536 MB and multiple of 64
MinValue: '128'
MaxValue: '1536'
Default: '128'
RoleARN:
Type: String
Description: Role ARN for this function
Runtime:
Type: String
Description: Runtime Environment name e.g nodejs, java8
AllowedPattern: ^(nodejs6.10|nodejs4.3|java8)$
ConstraintDescription: must be a valid environment (nodejs6.10|nodejs4.3|java8) name.
Timeout:
Type: Number
Description: Timeout in seconds
Default: '3'
Env1:
Type: String
Description: Environment Variable with format Key|value
Default: ''
Env2:
Type: String
Description: Environment Variable with format Key|value
Default: ''
Env3:
Type: String
Description: Environment Variable with format Key|value
Default: ''
Env4:
Type: String
Description: Environment Variable with format Key|value
Default: ''
# Conditions
Conditions:
Env1Exist: !Not [ !Equals [!Ref Env1, '']]
Env2Exist: !Not [ !Equals [!Ref Env2, '']]
Env3Exist: !Not [ !Equals [!Ref Env3, '']]
Env4Exist: !Not [ !Equals [!Ref Env4, '']]
# Resources
Resources:
LambdaFunction:
Type: AWS::Lambda::Function
Properties:
Code:
S3Bucket: !Ref 'FunctionCodeS3Bucket'
S3Key: !Ref 'FunctionCodeS3Key'
Description: !Sub 'Lambda function for: ${FunctionName}'
Environment:
Variables:
'Fn::If':
- Env1Exist
-
- !Select [0, !Split ["|", !Ref Env1]]: !Select [1, !Split ["|", !Ref Env1]]
- 'Fn::If':
- Env2Exist
- !Select [0, !Split ["|", !Ref Env2]]: !Select [1, !Split ["|", !Ref Env2]]
- !Ref "AWS::NoValue"
- 'Fn::If':
- Env3Exist
- !Select [0, !Split ["|", !Ref Env3]]: !Select [1, !Split ["|", !Ref Env3]]
- !Ref "AWS::NoValue"
- 'Fn::If':
- Env4Exist
- !Select [0, !Split ["|", !Ref Env4]]: !Select [1, !Split ["|", !Ref Env4]]
- !Ref "AWS::NoValue"
- !Ref "AWS::NoValue"
FunctionName: !Ref 'FunctionName'
Handler: !Ref 'HandlerName'
MemorySize: !Ref 'MemorySize'
Role: !Ref 'RoleARN'
Runtime: !Ref 'Runtime'
Timeout: !Ref 'Timeout'
Outputs:
LambdaFunctionARN:
Value: !GetAtt 'LambdaFunction.Arn'
I want to inject the environment variables to the the function and that will be passed from parent stack as below:
# Resouces
Resources:
# Lambda for search Function
ChildStackLambdaFunction:
Type: AWS::CloudFormation::Stack
Properties:
TemplateURL: <<REF_TO_ABOVE_LAMBDA_STACK.yml>>
Parameters:
FunctionName: test
HandlerName: 'index.handler'
FunctionCodeS3Bucket: <<BUCKET_NAME>>
FunctionCodeS3Key: <<FUNCTION_DEPLOYMENT_NAME>>
MemorySize: '256'
RoleARN: <<ROLE_ARN>>
Runtime: nodejs6.10
Timeout: '60'
Env1: !Sub 'AWS_REGION|${AWS::Region}'
When I deploy this stack, I am getting below error. Can anybody help me to resolve this one?
Template format error: [/Resources/LambdaFunction/Type/Environment/Variables/Fn::If/1/0] map keys must be strings; received a map instead
Passing key-value parameter is referred from here

Answer 1

So, I tried so many ways to achieve this, but we can not pass the dynamic key-value pair to nested lambda stack from the parent stack. I had a confirmation from the AWS support that this is not possible as this moment.
They suggested a another way which I liked and implemented and its mentioned as below:
Pass the key: value pair as a JSON string and parse it appropriately in the lambda function.
Environment:
Variables:
Env1: '{"REGION": "REGION_VALUE", "ENDPOINT": "http://SOME_ENDPOINT"}'
This suggestion has a little overhead on programming to parse the JSON string, but at this moment I will recommend this as solution for above problem.

Answer 2

I achieved this with the PyPlate macro.
Take environment variables list in a commalimited
Parameters:
EnvVars:
Type: CommaDelimitedList
Description: Comma separated list of Env vars key=value pairs (key1=value1,key2=value2)
and use it in the Lambda Resource:
Environment:
Variables: |
#!PyPlate
output = dict()
for envVar in params['EnvVars']:
key, value = envVar.split('=')
output.update({key: value})

Answer 3

This is the right way to use global variables.
Globals:
Function:
Timeout: 60
Runtime: nodejs10.x
Environment:
Variables:
STAGE: !Ref Stage
DatabaseName: !Ref DatabaseName
DatabaseUsername: !Ref DatabaseUsername
DatabasePassword: !Ref DatabasePassword
DatabaseHostname: !Ref DatabaseHostname
AuthyAPIKey: !Ref AuthyApiKey