aws-cdk-lib: Fargate task check requires at least 21G of storage but docs say 20G is the mininum

[JoshMcCullough]

Describe the bug

When configuring a FargateTaskDefinition, passing ephemeralStorageGiB: 20 throws the following error, even though the docs suggest that 20G is the minimum allowed.

Ephemeral storage size must be between 21GiB and 200GiB

Regression Issue

• Select this option if this issue appears to be a regression.

Last Known Working CDK Version

No response

Expected Behavior

ephemeralStorageGiB: 20 should be allowed, or the docs should be updated.

Current Behavior

ephemeralStorageGiB: 20 is not allowed, minimum value must be 21.

Reproduction Steps

1. Configure a FargateTaskDefinition.
2. Set: ephemeralStorageGiB: 20
3. Try to synth.

Possible Solution

Fix aws-cdk-lib/aws-ecs/lib/fargate/fargate-task-definition.js to check `(props.ephemeralStorageGiB<20||props.ephemeralStorageGiB>200), or fix the docs.

Additional Information/Context

No response

CDK CLI Version

2.155.0

Framework Version

No response

Node.js Version

18.19.0

OS

Manjaro Linux

Language

TypeScript

Language Version

5.5.4

Other information

No response

[ashishdhingra]

• The error is thrown by the validation check here.

• Per AWS::ECS::TaskDefinition EphemeralStorage, SizeInGiB has the minimum supported value of 20 GiB and the maximum supported value of 200 GiB.

• The correct value is reflected in the documentation comment for FargateTaskDefinitionProps.ephemeralStorageGiB, where the default is 20. (also refer FargateTaskDefinition. ephemeralStorageGiB)

[mazyu36]

Hello.

I modified the if statement and attempted to deploy with 20GB, but I encountered the following error.
The current implementation seems correct.

It is also noted in the Management Console.

[ashishdhingra]

Hello.

I modified the if statement and attempted to deploy with 20GB, but I encountered the following error. The current implementation seems correct.

It is also noted in the Management Console.

@mazyu36 Good observation. I will revalidate and would probably open ticket with CloudFormation team for documentation correction.

[ashishdhingra]

Tried to bypass CDK validation using below code (uses escape hatch):

import * as ec2 from 'aws-cdk-lib/aws-ec2';
import * as cdk from 'aws-cdk-lib';
import * as ecs from 'aws-cdk-lib/aws-ecs';

import path = require('path');


export class CdktestStack extends cdk.Stack {
  constructor(scope: cdk.App, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    // Create an ECS cluster
    const vpc = ec2.Vpc.fromLookup(this, 'MyDefaultVpc', {
      isDefault: true
    });
    const cluster = new ecs.Cluster(this, 'Cluster', { vpc });

    // Add capacity to it
    cluster.addCapacity('DefaultAutoScalingGroupCapacity', {
      instanceType: new ec2.InstanceType("t2.xlarge"),
      desiredCapacity: 3,
    });

    const taskDefinition = new ecs.FargateTaskDefinition(this, 'TaskDef', { ephemeralStorageGiB: 21 });
    (taskDefinition.node.defaultChild as ecs.CfnTaskDefinition).addPropertyOverride('EphemeralStorage', 20);

    taskDefinition.addContainer('DefaultContainer', {
      image: ecs.ContainerImage.fromRegistry("amazon/amazon-ecs-sample"),
      memoryLimitMiB: 512,
    });

    // Instantiate an Amazon ECS Service
    const ecsService = new ecs.FargateService(this, 'FargateService', {
      cluster,
      taskDefinition,
    });
  }
}

Although it is able to set EphemeralStorage to 20 in CloudFormation template:

Resources:
  ...
  ...
  TaskDef54694570:
    Type: AWS::ECS::TaskDefinition
    Properties:
      ContainerDefinitions:
        - Essential: true
          Image: amazon/amazon-ecs-sample
          Memory: 512
          Name: DefaultContainer
      Cpu: "256"
      EphemeralStorage: 20
      Family: CdktestStackTaskDefB8572B74
      Memory: "512"
      NetworkMode: awsvpc
      RequiresCompatibilities:
        - FARGATE
      TaskRoleArn:
        Fn::GetAtt:
          - TaskDefTaskRole1EDB4A67
          - Arn
    Metadata:
      aws:cdk:path: CdktestStack/TaskDef/Resource
...

Running cdk deploy fails with the below error:

CdktestStack: deploying... [1/1]
CdktestStack: creating CloudFormation changeset...
11:43:56 AM | CREATE_FAILED        | AWS::ECS::TaskDefinition           | TaskDef54694570
Resource handler returned message: "Invalid request provided: Create TaskDefinition: EphemeralStorage size should be at least 21 (Service: AmazonECS; Status Code: 400; Erro
r Code: ClientException; Request ID: d75746d2-7eac-4c17-8114-56c25b9e8c14; Proxy: null)" (RequestToken: 45f51668-4303-c8cf-2610-189ffcbb2abc, HandlerErrorCode: InvalidReque
st)


 ❌  CdktestStack failed: Error: The stack named CdktestStack failed creation, it may need to be manually deleted from the AWS console: ROLLBACK_COMPLETE: Resource handler returned message: "Invalid request provided: Create TaskDefinition: EphemeralStorage size should be at least 21 (Service: AmazonECS; Status Code: 400; Error Code: ClientException; Request ID: d75746d2-7eac-4c17-8114-56c25b9e8c14; Proxy: null)" (RequestToken: 45f51668-4303-c8cf-2610-189ffcbb2abc, HandlerErrorCode: InvalidRequest)
    at FullCloudFormationDeployment.monitorDeployment (/opt/homebrew/lib/node_modules/aws-cdk/lib/index.js:452:10567)
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)
    at async Object.deployStack2 [as deployStack] (/opt/homebrew/lib/node_modules/aws-cdk/lib/index.js:455:200276)
    at async /opt/homebrew/lib/node_modules/aws-cdk/lib/index.js:455:181698

 ❌ Deployment failed: Error: The stack named CdktestStack failed creation, it may need to be manually deleted from the AWS console: ROLLBACK_COMPLETE: Resource handler returned message: "Invalid request provided: Create TaskDefinition: EphemeralStorage size should be at least 21 (Service: AmazonECS; Status Code: 400; Error Code: ClientException; Request ID: d75746d2-7eac-4c17-8114-56c25b9e8c14; Proxy: null)" (RequestToken: 45f51668-4303-c8cf-2610-189ffcbb2abc, HandlerErrorCode: InvalidRequest)
    at FullCloudFormationDeployment.monitorDeployment (/opt/homebrew/lib/node_modules/aws-cdk/lib/index.js:452:10567)
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)
    at async Object.deployStack2 [as deployStack] (/opt/homebrew/lib/node_modules/aws-cdk/lib/index.js:455:200276)
    at async /opt/homebrew/lib/node_modules/aws-cdk/lib/index.js:455:181698
cdk****************************************************

So the existing validation is correct as of now.

• Amazon ECS: EphemeralStorage API reference mentions the minimum supported value is 20 GiB and the maximum supported value is 200 GiB.
• AWS::ECS::TaskDefinition EphemeralStorage also mentions the minimum supported value is 20 GiB and the maximum supported value is 200 GiB.

[ashishdhingra]

@JoshMcCullough Looking at the AWS console screenshot, I now understand what is happening.

• It specifies that By default, your tasks hosted on AWS Fargate receive a minimum of 20 GiB of ephemeral storage..
• However, To specify a custom amount of ephemeral storage, specify a value between 21 GiB up to a maximum of 200 GiB.

In other words, when trying to explicitly specify EphemeralStorage in CloudFormation template, one needs to specify minimum value of 21 GiB. Specifying custom value as 20 GiB doesn't make sense since it would anyway default to this value if no value is specified.

Based on above understanding, the validation in CDK and the default value mentioned in documentation is correct. Please review and confirm if this issue could be closed.

Thanks,
Ashish

[JoshMcCullough]

Okay. It's strange that 20 is technically valid but only if you don't specify any value.

[ashishdhingra]

Okay. It's strange that 20 is technically valid but only if you don't specify any value.

@JoshMcCullough Yes, it's really strange and was confusing in the beginning until I noticed a note in AWS console. Closing this ticket for now. Feel free to open another ticket in case you see other issues.

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