Parameters in imported templates for an external VPC with Application Composer - AWS Application Composer
Limitations when importing list parameter types

Parameters in imported templates for an external VPC with Application Composer

When you import an existing template with parameters defined for the security groups and subnets of an external VPC, Application Composer provides a dropdown list to select your parameters from.

The following is an example of the Parameters section of an imported template:

...
Parameters:
  VPCSecurityGroups:
    Description: Security group IDs generated by Application Composer
    Type: List<AWS::EC2::SecurityGroup::Id>
  VPCSubnets:
    Description: Subnet IDs generated by Application Composer
    Type: List<AWS::EC2::Subnet::Id>
  VPCSubnet:
    Description: Subnet Id generated by Application Composer
    Type: AWS::EC2::Subnet::Id
...

When configuring an external VPC for a new Lambda function on the canvas, these parameters will be available from a dropdown list. The following is an example:

A dropdown list of values being offered for the Parameter type of the Subnet ID field for a Lambda function card.

Limitations when importing list parameter types

Normally, you can specify multiple security group and subnet identifiers for each Lambda function. If your existing template contains list parameter types, such as List<AWS::EC2::SecurityGroup::Id> or List<AWS::EC2::Subnet::Id>, you can only specify one identifier.

For more information on parameter lists type, see Supported AWS-specific parameter types in the AWS CloudFormation User Guide.

The following is an example of a template that defines VPCSecurityGroups as a list parameter type:

...
Parameters:
  VPCSecurityGroups:
    Description: Security group IDs generated by Application Composer
    Type: List<AWS::EC2::SecurityGroup::Id>
...

In Application Composer, if you select the VPCSecurityGroups value as a security group identifier for a Lambda function, you will see the following message:

A list parameter type named VPCSecurityGroups being provided for the Parameter type of the security group ID field of a Lambda function card.

This limitation occurs because the SecurityGroupIds and SubnetIds properties of an AWS::Lambda::Function VpcConfig object both accept only a list of string values. Since a single list parameter type contains a list of strings, it can be the only object provided when specified.

For list parameter types, the following is an example of how they are defined in the template when configured with a Lambda function:

...
Parameters:
  VPCSecurityGroups:
    Description: Security group IDs generated by Application Composer
    Type: List<AWS::EC2::SecurityGroup::Id>
  VPCSubnets:
    Description: Subnet IDs generated by Application Composer
    Type: List<AWS::EC2::Subnet::Id>
Resources:
  ...
  MyFunction:
    Type: AWS::Serverless::Function
    Properties:
      ...
      VpcConfig:
        SecurityGroupIds: !Ref VPCSecurityGroups
        SubnetIds: !Ref VPCSubnets