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Read this on the main serverless docs site

AWS Infrastructure Resources

If you are using AWS as a provider for your Service, all Resources are other AWS infrastructure resources which the AWS Lambda functions in your Service depend on, like AWS DynamoDB or AWS S3.

Using the Serverless Framework, you can define the infrastructure resources you need in serverless.yml, and easily deploy them.

Configuration

Every stage you deploy to with serverless.yml using the aws provider is a single AWS CloudFormation stack. This is where your AWS Lambda functions and their event configurations are defined and it's how they are deployed. When you add resources those resources are added into your CloudFormation stack upon serverless deploy.

Define your AWS resources in a property titled resources. What goes in this property is raw CloudFormation template syntax, in YAML, like this:

# serverless.yml

service: usersCrud
provider: aws
functions:

resources: # CloudFormation template syntax
  Resources:
    usersTable:
      Type: AWS::DynamoDB::Table
      Properties:
        TableName: usersTable
        AttributeDefinitions:
          - AttributeName: email
            AttributeType: S
        KeySchema:
          - AttributeName: email
            KeyType: HASH
        ProvisionedThroughput:
          ReadCapacityUnits: 1
          WriteCapacityUnits: 1

You can attach any kind of resource to your CloudFormation stack. You can add Resources, Outputs. You can also use Serverless Variables for sensitive data or reusable configuration in your resources templates.

Note: By supplying your resources at resources.Resources you may accidentally override resources as generated by the framework. To intentionally extend such resources, please use resources.extensions, see Override AWS CloudFormation Resource section for more info.

Note: You can now remove resource properties with null assignment. Since CloudFormation does not allow this, Serverless will strip these properties from the final template before upload.

AWS CloudFormation Resource Reference

To have consistent naming in the CloudFormation Templates that get deployed we use a standard pattern:

{Function Name}{Cloud Formation Resource Type}{Resource Name}{SequentialID, instanceId or Random String}

  • Function Name - This is optional for Resources that should be recreated when the function name gets changed. Those resources are also called function bound
  • Cloud Formation Resource Type - E.g., S3Bucket
  • Resource Name - An identifier for the specific resource, e.g. for an S3 Bucket the configured bucket name.
  • SequentialID, instanceId or Random String - For a few resources we need to add an optional sequential id, the Serverless instanceId (accessible via ${sls:instanceId}) or a random string to identify them

All resource names that are deployed by Serverless have to follow this naming scheme. The only exception (for backwards compatibility reasons) is the S3 Bucket that is used to upload artifacts so they can be deployed to your function.

We're also using the term normalizedName or similar terms in this guide. This means dropping any characters that aren't allowed in resources names, e.g. special characters.

If you have path variables in your url, they get normalized too, and there is a Var added implicitly. So normalizedPath for POST /users/{user_id} will be normalized to UsersUseridVarTestPost

Tip: If you are unsure how a resource is named, that you want to reference from your custom resources, you can issue a serverless package. This will create the CloudFormation template for your service in the .serverless folder (it is named cloudformation-template-update-stack.json). Just open the file and check for the generated resource name.

AWS Resource Name Template Example
S3::Bucket S3Bucket{normalizedBucketName} S3BucketMybucket
IAM::Role IamRoleLambdaExecution IamRoleLambdaExecution
Lambda::Function {normalizedFunctionName}LambdaFunction HelloLambdaFunction
Lambda::Url {normalizedFunctionName}LambdaFunctionUrl HelloLambdaFunctionUrl
Lambda::Version {normalizedFunctionName}LambdaVersion{sha256} HelloLambdaVersionr3pgoTvv1xT4E4NiCL6JG02fl6vIyi7OS1aW0FwAI
Logs::LogGroup {normalizedFunctionName}LogGroup HelloLogGroup
Lambda::Permission
  • Schedule: {normalizedFunctionName}LambdaPermissionEventsRuleSchedule{index}
  • CloudWatch Event: {normalizedFunctionName}LambdaPermissionEventsRuleCloudWatchEvent{index}
  • CloudWatch Log: {normalizedFunctionName}LambdaPermissionLogsSubscriptionFilterCloudWatchLog{index}
  • IoT: {normalizedFunctionName}LambdaPermissionIotTopicRule{index}
  • S3: {normalizedFunctionName}LambdaPermission{normalizedBucketName}S3
  • APIG: {normalizedFunctionName}LambdaPermissionApiGateway
  • SNS: {normalizedFunctionName}LambdaPermission{normalizedTopicName}SNS
  • Alexa Skill: {normalizedFunctionName}LambdaPermissionAlexaSkill
  • Alexa Smart Home: {normalizedFunctionName}LambdaPermissionAlexaSmartHome{index}
  • Cognito User Pool Trigger Source: {normalizedFunctionName}LambdaPermissionCognitoUserPool{normalizedPoolId}TriggerSource{triggerSource}
  • Schedule: HelloLambdaPermissionEventsRuleSchedule1
  • CloudWatch Event: HelloLambdaPermissionEventsRuleCloudWatchEvent1
  • CloudWatch Log: HelloLambdaPermissionLogsSubscriptionFilterCloudWatchLog1
  • IoT: HelloLambdaPermissionIotTopicRule1
  • S3: HelloLambdaPermissionBucketS3
  • APIG: HelloLambdaPermissionApiGateway
  • SNS: HelloLambdaPermissionTopicSNS
  • Alexa Skill: HelloLambdaPermissionAlexaSkill
  • Alexa Smart Home: HelloLambdaPermissionAlexaSmartHome1
  • Cognito User Pool Trigger Source: HelloLambdaPermissionCognitoUserPoolMyPoolTriggerSourceCustomMessage
Events::Rule
  • Schedule: {normalizedFunctionName}EventsRuleSchedule{SequentialID}
  • CloudWatch Event: {normalizedFunctionName}EventsRuleCloudWatchEvent{SequentialID}
  • Schedule: HelloEventsRuleSchedule1
  • CloudWatch Event: HelloEventsRuleCloudWatchEvent1
AWS::Logs::SubscriptionFilter {normalizedFunctionName}LogsSubscriptionFilterCloudWatchLog{SequentialID} HelloLogsSubscriptionFilterCloudWatchLog1
AWS::IoT::TopicRule {normalizedFunctionName}IotTopicRule{SequentialID} HelloIotTopicRule1
ApiGateway::RestApi ApiGatewayRestApi ApiGatewayRestApi
ApiGateway::Resource ApiGatewayResource{normalizedPath} ApiGatewayResourceUsers
ApiGateway::Method ApiGatewayMethod{normalizedPath}{normalizedMethod} ApiGatewayMethodUsersGet
ApiGateway::Authorizer {normalizedFunctionName}ApiGatewayAuthorizer HelloApiGatewayAuthorizer
ApiGateway::Deployment ApiGatewayDeployment{instanceId} ApiGatewayDeployment12356789
ApiGateway::ApiKey ApiGatewayApiKey{OptionalNormalizedName}{SequentialID} ApiGatewayApiKeyFree1
ApiGateway::UsagePlan ApiGatewayUsagePlan{OptionalNormalizedName} ApiGatewayUsagePlanFree
ApiGateway::UsagePlanKey ApiGatewayUsagePlanKey{OptionalNormalizedName}{SequentialID} ApiGatewayUsagePlanKeyFree1
ApiGateway::Stage ApiGatewayStage ApiGatewayStage
SNS::Topic SNSTopic{normalizedTopicName} SNSTopicSometopic
SNS::Subscription {normalizedFunctionName}SnsSubscription{normalizedTopicName} HelloSnsSubscriptionSomeTopic
AWS::Lambda::EventSourceMapping
  • DynamoDB: {normalizedFunctionName}EventSourceMappingDynamodb{tableName}
  • Kinesis: {normalizedFunctionName}EventSourceMappingKinesis{streamName}
  • DynamoDB: HelloLambdaEventSourceMappingDynamodbUsers
  • Kinesis: HelloLambdaEventSourceMappingKinesisMystream
Cognito::UserPool CognitoUserPool{normalizedPoolId} CognitoUserPoolPoolId

Override AWS CloudFormation Resource

You can override the specific CloudFormation resource to apply your own options (place all such extensions at resources.extensions section). For example, if you want to set AWS::Logs::LogGroup retention time to 30 days, override it with above table's Name Template.

When you override basic resources, there are two things to keep in mind when it comes to normalizedFunctionName:

  • It should start with an uppercase character
  • The - will be changed to Dash, _ will be changed to Underscore

Here's an example:

functions:
  write-post:
    handler: handler.writePost
    events:
      - httpApi: 'POST /api/posts/new'

resources:
  extensions:
    WriteDashPostLogGroup:
      Properties:
        RetentionInDays: '30'

Here's how the extension logic is defined:

Resource attribute Operation
Condition Set to extension value if present.
CreationPolicy Set to extension value if present.
DeletionPolicy Set to extension value if present.
DependsOn Merge. The extension value will be added to the resource's DependsOn list.
Metadata Merge. If a metadata key with the same name exists in the resource, the value will be replaced with the extension value.
Properties Merge. If a property with the same name exists in the resource, the value will be replaced with the extension value.
UpdatePolicy Set to extension value if present.
UpdateReplacePolicy Set to extension value if present.
other Not supported. An error will be thrown if you try to extend an unsupported attribute.

Extending using resources.extensions only works on the Resources part of the CloudFormation template.