Not Error out on AWS Lambda VPC config if both subnet_ids and security_group_ids are empty. (#6191)

AWS Lambda VPC config is an optional configuration and which needs to both subnet_ids and
security_group_ids to tie the lambda function to a VPC. We should make it optional if
both subnet_ids and security_group_ids are not net which would add better flexiblity in
creation of more useful modules as there are "if else" checks. Without this we are creating
duplicate modules one with VPC and one without VPC resulting in various anomalies.

builtin/providers/aws/resource_aws_lambda_function.go

@@ -181,19 +181,21 @@ func resourceAwsLambdaFunctionCreate(d *schema.ResourceData, meta interface{}) e
 			return err
 		}
 
-		var subnetIds []*string
-		for _, id := range config["subnet_ids"].(*schema.Set).List() {
-			subnetIds = append(subnetIds, aws.String(id.(string)))
-		}
+		if config != nil {
+			var subnetIds []*string
+			for _, id := range config["subnet_ids"].(*schema.Set).List() {
+				subnetIds = append(subnetIds, aws.String(id.(string)))
+			}
 
-		var securityGroupIds []*string
-		for _, id := range config["security_group_ids"].(*schema.Set).List() {
-			securityGroupIds = append(securityGroupIds, aws.String(id.(string)))
-		}
+			var securityGroupIds []*string
+			for _, id := range config["security_group_ids"].(*schema.Set).List() {
+				securityGroupIds = append(securityGroupIds, aws.String(id.(string)))
+			}
 
-		params.VpcConfig = &lambda.VpcConfig{
-			SubnetIds:        subnetIds,
-			SecurityGroupIds: securityGroupIds,
+			params.VpcConfig = &lambda.VpcConfig{
+				SubnetIds:        subnetIds,
+				SecurityGroupIds: securityGroupIds,
+			}
 		}
 	}
 
@@ -402,6 +404,11 @@ func validateVPCConfig(v interface{}) (map[string]interface{}, error) {
 		return nil, errors.New("vpc_config is <nil>")
 	}
 
+	// if subnet_ids and security_group_ids are both empty then the VPC is optional
+	if config["subnet_ids"].(*schema.Set).Len() == 0 && config["security_group_ids"].(*schema.Set).Len() == 0 {
+		return nil, nil
+	}
+
 	if config["subnet_ids"].(*schema.Set).Len() == 0 {
 		return nil, errors.New("vpc_config.subnet_ids cannot be empty")
 	}

website/source/docs/providers/aws/r/lambda_function.html.markdown

@@ -65,6 +65,8 @@ resource "aws_lambda_function" "test_lambda" {
 * `subnet_ids` - (Required) A list of subnet IDs associated with the Lambda function.
 * `security_group_ids` - (Required) A list of security group IDs associated with the Lambda function.
 
+~> **NOTE:** if both `subnet_ids` and `security_group_ids` are empty then vpc_config is considered to be empty or unset.
+
 ## Attributes Reference
 
 * `arn` - The Amazon Resource Name (ARN) identifying your Lambda Function.