Checkboxes for prior research

• I've gone through Developer Guide and API reference
• I've checked AWS Forums and StackOverflow.
• I've searched for previous similar issues and didn't find any solution.

Describe the bug

Regression where any Date sent in ValidFrom/ValidUntil causes an error to be thrown. The crash is reported by the server and seems to be related to the milliseconds.

Regression Issue

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

SDK version number

@aws-sdk/client-ec2@npm:3.817.0

Which JavaScript Runtime is this issue in?

Node.js

Details of the browser/Node.js/ReactNative version

18.20.4

Reproduction Steps

Note that I've redacted some things.

yarn add @aws-sdk/client-ec2

// test.js
import { EC2Client, RequestSpotFleetCommand } from '@aws-sdk/client-ec2';

const client = new EC2Client({ region: 'us-east-1' });
const dryRun = false;
await client.send(new RequestSpotFleetCommand({
  DryRun: dryRun,
  SpotFleetRequestConfig: {
    IamFleetRole: 'arn:aws:iam::REDACTED',
    AllocationStrategy: 'capacityOptimized',
    TargetCapacity: 1,
    ValidUntil: new Date(Date.now() + (1000 * 60 * 60)),
    TerminateInstancesWithExpiration: true,
    Type: 'maintain',
    TargetCapacityUnitType: 'units',
    LaunchSpecifications: [
      {
        ImageId: 'ami-REDACTED',
        BlockDeviceMappings: [
          {
            DeviceName: '/dev/sda1',
            Ebs: {
              DeleteOnTermination: true,
              VolumeType: 'gp2',
              VolumeSize: 8,
              SnapshotId: 'snap-REDACTED',
            },
          },
        ],
        IamInstanceProfile: {
          Arn: 'arn:aws:iam::REDACTED',
        },
        KeyName: 'REDACTED',
        SecurityGroups: [
          {
            GroupId: 'sg-REDACTED',
          },
        ],
        UserData: 'REDACTED',
        InstanceRequirements: {
          VCpuCount: {
            Min: 8,
            Max: 8,
          },
          MemoryMiB: {
            Min: 4096,
          },
          SpotMaxPricePercentageOverLowestPrice: 100,
        },
      },
    ],
  },
}));

node test.js

Note the ValidUntil prop.

Observed Behavior

node_modules/@smithy/smithy-client/dist-cjs/index.js:379
  const response = new exceptionCtor({
                   ^

InvalidSpotFleetRequestConfig: Parameter: SpotFleetRequestConfig.ValidUntil is invalid.
    at throwDefaultError (node_modules/@smithy/smithy-client/dist-cjs/index.js:379:20)
    at node_modules/@smithy/smithy-client/dist-cjs/index.js:388:5
    at de_CommandError (node_modules/@aws-sdk/client-ec2/dist-cjs/index.js:17188:10)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async node_modules/@smithy/middleware-serde/dist-cjs/index.js:36:20
    at async node_modules/@smithy/core/dist-cjs/index.js:193:18
    at async node_modules/@smithy/middleware-retry/dist-cjs/index.js:320:38
    at async node_modules/@aws-sdk/middleware-logger/dist-cjs/index.js:33:22
    at <anonymous> (test.ts:5:18) {
  '$fault': 'client',
  '$metadata': {
    httpStatusCode: 400,
    requestId: '0856c9e6-159e-482c-8c2b-ee3fa2965def',
    extendedRequestId: undefined,
    cfId: undefined,
    attempts: 1,
    totalRetryDelay: 0
  },
  Code: 'InvalidSpotFleetRequestConfig'
}

Expected Behavior

It should start the fleet request.

Possible Solution

Must support Date in ValidFrom/ValidUntil (as the typescript definitions suggests).

Additional Information/Context

Note that:

• If I set dryRun to true, it doesn't error.
• If I downgrade to @aws-sdk/client-ec2 3.427.0 it works.
• If I change ValidUntil to { toISOString: () => new Date(Date.now() + (1000 * 60 * 60)).toISOString().replace(/\.\d+Z$/, 'Z') } it works.

This suggests that the @aws-sdk/client-ec2 client calls Date.toISOString() on ValidFrom/ValidUntil and then sends to the server what is returned from those (e.g. 2025-05-26T21:37:50.051Z), however the server expects 2025-05-26T21:37:50Z (no milliseconds).

How am I the only person who seems to have hit this obvious bug in the JS SDK?

Related: boto/boto3#714