Cloudformation: Invalid permissions on Lambda function found with API GW Integration - aws-lambda

Question

This is my cloudformation template, which deploys successfully:
AWSTemplateFormatVersion: "2010-09-09"
Transform: AWS::Serverless-2016-10-31
Description: Deploy Da Blog
Resources:
ArticleTable:
Type: AWS::DynamoDB::Table
Properties:
KeySchema:
- AttributeName: id
KeyType: HASH
AttributeDefinitions:
- AttributeName: id
AttributeType: S
ProvisionedThroughput:
ReadCapacityUnits: 1
WriteCapacityUnits: 1
TableName: !Sub ${AWS::StackName}-Article
UpdateReplacePolicy: Retain
DeletionPolicy: Retain
############################### BLOG API ############################
BlogRestApiLogGroup:
Type: AWS::Logs::LogGroup
Properties:
LogGroupName: !Sub '/aws/apigateway/${AWS::StackName}'
BlogRestApiLoggingRole:
Type: AWS::IAM::Role
Properties:
RoleName: !Sub 'BlogRestApiLoggingRole-${AWS::StackName}'
AssumeRolePolicyDocument:
Version: 2012-10-17
Statement:
- Effect: Allow
Principal:
Service: apigateway.amazonaws.com
Action:
- sts:AssumeRole
ManagedPolicyArns:
- arn:aws:iam::aws:policy/service-role/AmazonAPIGatewayPushToCloudWatchLogs
## specifies the IAM role that Amazon API Gateway uses to write API logs to Amazon CloudWatch Logs
BlogRestApiAccount:
Type: AWS::ApiGateway::Account
Properties:
CloudWatchRoleArn: !GetAtt [ BlogRestApiLoggingRole, Arn ]
BlogRestApi:
Type: AWS::ApiGateway::RestApi
Properties:
Name: !Sub '${AWS::StackName}'
Description: Blog API
EndpointConfiguration:
Types:
- EDGE
BlogRestApiDeployment:
Type: AWS::ApiGateway::Deployment
Properties:
RestApiId: !Ref BlogRestApi
Description: Automatically created by the RestApi construct
DependsOn:
- BlogRestApi
- BlogApiResource
- BlogApiIdResource
- ListArticlesMethod
- PostArticleMethod
- GetArticleMethod
BlogRestApiStageProd:
Type: AWS::ApiGateway::Stage
DependsOn:
- BlogRestApiDeployment
Properties:
RestApiId: !Ref BlogRestApi
DeploymentId: !Ref BlogRestApiDeployment
StageName: prod
MethodSettings:
- LoggingLevel: INFO
ResourcePath: '/*'
HttpMethod: '*'
MetricsEnabled: true
BlogApiRole:
Type: AWS::IAM::Role
Properties:
RoleName: !Sub 'BlogApiRole-${AWS::StackName}'
AssumeRolePolicyDocument:
Version: 2012-10-17
Statement:
- Effect: Allow
Principal:
Service: apigateway.amazonaws.com
Action:
- sts:AssumeRole
BlogApiPolicy:
Type: AWS::IAM::Policy
DependsOn:
- BlogApiRole
- ListArticlesFunction
- PostArticleFunction
- GetArticleFunction
Properties:
PolicyName: !Sub 'BlogApiPolicy-${AWS::StackName}'
PolicyDocument:
Version: 2012-10-17
Statement:
- Effect: 'Allow'
Action: 'lambda:InvokeFunction'
Resource:
- !GetAtt ListArticlesFunction.Arn
- !GetAtt PostArticleFunction.Arn
- !GetAtt GetArticleFunction.Arn
Roles:
- !Ref BlogApiRole
############################### END OF Blog API ############################
############################### START OF Blog Functions ####################
BlogApiResource:
Type: AWS::ApiGateway::Resource
Properties:
ParentId: !GetAtt [ BlogRestApi, RootResourceId ]
PathPart: article
RestApiId: !Ref BlogRestApi
BlogApiIdResource:
Type: AWS::ApiGateway::Resource
Properties:
ParentId: !Ref BlogApiResource
PathPart: "{id}"
RestApiId: !Ref BlogRestApi
BlogApiOptionsMethod:
Type: AWS::ApiGateway::Method
DependsOn:
- BlogApiResource
Properties:
ApiKeyRequired: true
AuthorizationType: NONE
HttpMethod: OPTIONS
Integration:
Type: MOCK
PassthroughBehavior: WHEN_NO_TEMPLATES
RequestTemplates:
'application/json': '{"statusCode": 200}'
IntegrationResponses:
- StatusCode: 200
ResponseParameters:
method.response.header.Access-Control-Allow-Headers: "'Content-Type,X-Amz-Date,Authorization,X-Api-Key,X-Amz-Security-Token'"
method.response.header.Access-Control-Allow-Methods: "'GET,POST,PATCH,OPTIONS'"
method.response.header.Access-Control-Allow-Origin: "'*'"
ResponseTemplates:
'application/json': '{}'
MethodResponses:
- StatusCode: 200
ResponseParameters:
method.response.header.Access-Control-Allow-Headers: false
method.response.header.Access-Control-Allow-Methods: false
method.response.header.Access-Control-Allow-Origin: false
ResourceId: !Ref BlogApiResource
RestApiId: !Ref BlogRestApi
ListArticlesFunction:
Type: AWS::Serverless::Function
Properties:
FunctionName: !Sub '${AWS::StackName}-list-articles-function'
Handler: com.zenithwebfoundry.blog.api.ListArticlesHandler
CodeUri:
Key: !Ref ParamCodePackage
Bucket: !Ref ParamCodeBucket
Policies:
- Version: '2012-10-17'
Statement:
- Effect: Allow
Action:
- dynamodb:Query
Resource: !GetAtt [ ArticleTable, Arn ]
Runtime: java11
Timeout: 10
MemorySize: 256
Environment:
Variables:
TABLE_NAME: !Ref ArticleTable
PRIMARY_KEY: id
DependsOn:
- ArticleTable
ListArticlesMethod:
Type: AWS::ApiGateway::Method
Properties:
HttpMethod: GET
ResourceId: !Ref BlogApiResource
RestApiId: !Ref BlogRestApi
AuthorizationType: NONE
Integration:
IntegrationHttpMethod: POST
Type: AWS
Uri: !Sub 'arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${ListArticlesFunction.Arn}/invocations'
PassthroughBehavior: WHEN_NO_TEMPLATES
RequestTemplates:
'application/json': !Ref ParamAPIGatewayRequestEventMappingTemplate
IntegrationResponses:
- StatusCode: 200
ResponseTemplates:
'application/json': !Ref ParamAPIGatewayResponseEventMappingTemplate
MethodResponses:
- StatusCode: 200
OperationName: ListArticles
PostArticleFunction:
Type: AWS::Serverless::Function
Properties:
FunctionName: !Sub '${AWS::StackName}-post-article-function'
Handler: com.zenithwebfoundry.blog.api.SaveArticleHandler
CodeUri:
Key: !Ref ParamCodePackage
Bucket: !Ref ParamCodeBucket
Policies:
- Version: '2012-10-17'
Statement:
- Effect: Allow
Action:
- dynamodb:PutItem
Resource: !GetAtt [ ArticleTable, Arn ]
Runtime: java11
Timeout: 10
MemorySize: 256
Environment:
Variables:
TABLE_NAME: !Ref ArticleTable
PRIMARY_KEY: id
DependsOn:
- ArticleTable
PostArticleMethod:
Type: AWS::ApiGateway::Method
Properties:
HttpMethod: POST
ResourceId: !Ref BlogApiResource
RestApiId: !Ref BlogRestApi
AuthorizationType: NONE
Integration:
IntegrationHttpMethod: POST
Type: AWS
Uri: !Sub 'arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${PostArticleFunction.Arn}/invocations'
PassthroughBehavior: WHEN_NO_TEMPLATES
RequestTemplates:
'application/json': !Ref ParamAPIGatewayRequestEventMappingTemplate
IntegrationResponses:
- StatusCode: 200
ResponseTemplates:
'application/json': !Ref ParamAPIGatewayResponseEventMappingTemplate
MethodResponses:
- StatusCode: 200
OperationName: PostArticle
GetArticleFunction:
Type: AWS::Serverless::Function
Properties:
FunctionName: !Sub '${AWS::StackName}-get-article-function'
Handler: com.zenithwebfoundry.blog.api.GetArticleHandler
CodeUri:
Key: !Ref ParamCodePackage
Bucket: !Ref ParamCodeBucket
Policies:
- Version: '2012-10-17'
Statement:
- Effect: Allow
Action:
- dynamodb:GetItem
Resource: !GetAtt [ ArticleTable, Arn ]
Runtime: java11
Timeout: 10
MemorySize: 256
Environment:
Variables:
TABLE_NAME: !Ref ArticleTable
PRIMARY_KEY: id
DependsOn:
- ArticleTable
GetArticleMethod:
Type: AWS::ApiGateway::Method
Properties:
HttpMethod: GET
ResourceId: !Ref BlogApiIdResource
RestApiId: !Ref BlogRestApi
AuthorizationType: NONE
Integration:
IntegrationHttpMethod: POST
Type: AWS
Uri: !Sub 'arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${GetArticleFunction.Arn}/invocations'
PassthroughBehavior: WHEN_NO_TEMPLATES
RequestTemplates:
'application/json': !Ref ParamAPIGatewayRequestEventMappingTemplate
IntegrationResponses:
- StatusCode: 200
ResponseTemplates:
'application/json': !Ref ParamAPIGatewayResponseEventMappingTemplate
MethodResponses:
- StatusCode: 200
OperationName: GetArticle
############################### END OF Blog Functions ######################
BlogAPIDomainName:
Type: AWS::ApiGateway::DomainName
Properties:
DomainName: !Join [ ".", ['blogapi', !Ref DomainName]]
EndpointConfiguration:
Types:
- EDGE
CertificateArn: !Ref DomainCert
SecurityPolicy: TLS_1_0
BlogAPIHostedZone:
Type: AWS::Route53::HostedZone
Properties:
Name: !Ref BlogAPIDomainName
BlogAPIBasePathMapping:
Type: AWS::ApiGateway::BasePathMapping
Properties:
DomainName: !Ref BlogAPIDomainName
RestApiId: !Ref BlogRestApi
Stage: 'prod'
Route53RecordSetGroup:
Type: AWS::Route53::RecordSetGroup
Properties:
HostedZoneId: !Ref DomainHostedZoneId
RecordSets:
- Name: !Join [ "", ['blog', '.', !Ref DomainName, '.']]
Type: A
TTL: '300'
ResourceRecords:
- 52.64.238.177
- Name: !Join [ ".", ['blogapi', !Ref DomainName]]
Type: A
AliasTarget:
# HostedZoneId: !Ref BlogAPIHostedZone # distributionHostedZoneId - alias target name does not lie in the target zone
HostedZoneId: Z2FDTNDATAQYW2
# https://j97h8bvml9.execute-api.ap-southeast-2.amazonaws.com/prod/articles
DNSName: !GetAtt [BlogAPIDomainName, DistributionDomainName]
AssetsBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Join [ ".", [ !Ref 'AWS::StackName', 'assets' ] ]
CorsConfiguration:
CorsRules:
- AllowedHeaders: ['*']
AllowedMethods: [GET,PUT,POST,DELETE,HEAD]
AllowedOrigins: ['http://localhost*']
PublicAccessBlockConfiguration:
BlockPublicAcls: true
BlockPublicPolicy: true
IgnorePublicAcls: true
RestrictPublicBuckets: true
WebBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Join [ ".", [ !Ref 'AWS::StackName', 'web' ] ]
PublicAccessBlockConfiguration:
BlockPublicAcls: true
BlockPublicPolicy: true
IgnorePublicAcls: true
RestrictPublicBuckets: true
WebsiteConfiguration:
IndexDocument: 'index.html'
ErrorDocument: 'index.html'
Parameters:
ParamCodePackage:
Type: String
ParamCodeBucket:
Type: String
DomainName:
Description: "Public DNS Zone Name"
Type: String
DomainHostedZoneId:
Type: String
Description: 'The AWS HostedZoneId of the above domain name'
DomainCert:
Type: String
Description: 'The arn reference to the certificate used with the domain.'
ParamRequestMappingTemplate:
Type: String
Description: 'Read from resources/templates'
SaveArticleHandler:
Type: String
Default: 'com.zenithwebfoundry.blog.api.SaveArticleHandler'
GetArticleHandler:
Type: String
Default: 'com.zenithwebfoundry.blog.api.GetArticleHandler'
ListArticlesHandler:
Type: String
Default: 'com.zenithwebfoundry.blog.api.ListArticlesHandler'
ParamAPIGatewayRequestEventMappingTemplate:
Type: String
Default: '{
"resource" : "$context.resourceId",
"path" : "$context.path",
"httpMethod" : "$context.httpMethod",
"headers": {
#foreach($header in $input.params().header.keySet())
"$header": "$util.escapeJavaScript($input.params().header.get($header))" #if($foreach.hasNext),#end
#end
},
"method": "$context.httpMethod",
"pathParameters": {
#foreach($param in $input.params().path.keySet())
"$param": "$util.escapeJavaScript($input.params().path.get($param))" #if($foreach.hasNext),#end
#end
},
"queryStringParameters": {
#foreach($queryParam in $input.params().querystring.keySet())
"$queryParam": "$util.escapeJavaScript($input.params().querystring.get($queryParam))" #if($foreach.hasNext),#end
#end
},
"body" : $input.json("$"),
"isBase64Encoded": false
}'
ParamAPIGatewayResponseEventMappingTemplate:
Type: String
Default: '#set($statusCode = $input.path("$.statusCode"))
#set($context.responseOverride.status = $statusCode)
#set($headers = $input.path("$.headers"))
#foreach($key in $headers.keySet())
#set($context.responseOverride.header[$key] = $headers[$key])
#end
#set($context.responseOverride.header.Access-Control-Allow-Headers = "Content-Type,X-Amz-Date,Authorization,X-Api-Key,X-Amz-Security-Token")
#set($context.responseOverride.header.Access-Control-Allow-Methods = "*")
#set($context.responseOverride.header.Access-Control-Allow-Origin = "*")
{
"body": $input.json("$.body")
}
'
Outputs:
ArticleEndpoint:
Value: !Join ["", ['https://', !Ref BlogRestApi, '.execute-api.ap-southeast-2.', !Ref 'AWS::URLSuffix', '/', !Ref BlogRestApiStageProd, '/'] ]
The problem is that when I try to call the ListArticlesFunction using the following curl expression:
curl -i -H "Accept: application/json" -H "Content-Type: application/json" -X GET https://blogapi.zenithwebfoundry.com/article
I get the following:
HTTP/2 500
content-type: application/json
content-length: 36
date: Sun, 30 Aug 2020 09:09:50 GMT
x-amzn-requestid: c1948ed5-18c5-4807-8904-3c1c2af06c25
x-amzn-errortype: InternalServerErrorException
x-amz-apigw-id: SE3y1G71ywMF5fw=
x-cache: Error from cloudfront
via: 1.1 647846f53eba457a8e4ba1d1d42a6336.cloudfront.net (CloudFront)
x-amz-cf-pop: SYD1-C1
x-amz-cf-id: 6bnMhNRUdf1znTmD0vQn86UZcMF_j9JCzFb-JvhwwT9j6ch4P8t20g==
{"message": "Internal server error"}
Checking cloudwatch, I see the slightly cryptic error:
Execution failed due to configuration error: Invalid permissions on Lambda function
The same thing happens if I go into the APIGateway service console and go to the article GET resource. So at least its consistent.
I have tested the handler in isolation and there's no compilation problems anywhere, so I'm pretty sure its stack-related.
I gather that the problem must either be in the BlogApiPolicy Policy or the Lambda Policy, but nothing I set seems to work. Does anyone know what cloudformation shenanigans is needed to get this right?

Answer 1

The answer is that I needed the role added as a Credentials: entry in the method of each Lambda, for example:
ListArticlesMethod:
Type: AWS::ApiGateway::Method
Properties:
HttpMethod: GET
ResourceId: !Ref BlogApiResource
RestApiId: !Ref BlogRestApi
AuthorizationType: NONE
Integration:
IntegrationHttpMethod: POST
Type: AWS
Uri: !Sub 'arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${ListArticlesFunction.Arn}/invocations'
Credentials: !GetAtt [BlogApiRole, Arn]
PassthroughBehavior: WHEN_NO_TEMPLATES
RequestTemplates:
'application/json': !Ref ParamAPIGatewayRequestEventMappingTemplate
IntegrationResponses:
- StatusCode: 200
ResponseTemplates:
'application/json': !Ref ParamAPIGatewayResponseEventMappingTemplate
MethodResponses:
- StatusCode: 200
OperationName: ListArticles
Why this is suddenly needed, when this was never needed before, is quite beyond me, but I must thank #Marcin for his/her patient assistance and convincing my doubting mind.

Answer 2

Based on the comments.
The issue was that BlogApiRole, although being created, it was not used in any of the API Gateway methods. This is required, because API Gateway needs to have explicit permissions to invoke a lambda functions. To enable this, Credentials in AWS::ApiGateway::Method Integration should be set.
The alternative is to use AWS::Lambda::Permission. The use of the AWS::Lambda::Permission is especially useful when there are many methods in the API gateway which require invoking the lambda. The reason is that you can create one such AWS::Lambda::Permission for the lambda function which can allow API gateway access to the lambda as a whole. This saves us from defining Credentials for each method independently.