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Windows EC2 memory hog

Consume a configurable amount of memory (absolute or percentage) on one or more Windows EC2 instances (selected by ID or tag) for a configurable duration so you can test how Windows-hosted workloads b

Windows EC2 memory hog is an AWS chaos fault that allocates MEMORY_CONSUMPTION MB (or MEMORY_PERCENTAGE percent of total memory) on one or more Windows EC2 instances for a configurable duration. Targets are selected by EC2_INSTANCE_ID or EC2_INSTANCE_TAG. The fault dispatches a PowerShell allocation command via AWS Systems Manager Run Command and releases the memory at the end of the fault.

Use this fault to test how a Windows-hosted workload behaves under sustained memory pressure: whether the application sheds load when memory is tight, whether the working set spills to swap (paging file), and whether memory-based monitoring catches the pressure quickly.

RUN YOUR FIRST EXPERIMENT

If you have not configured the chaos infrastructure yet, go to Quickstart to install the chaos infrastructure and run an experiment end to end.

Use cases

Run this fault when you want to answer concrete questions like:

  • Memory pressure handling: When free memory shrinks, does the application sustain throughput, or does paging cause throughput collapse?

  • Service recovery: Do Windows services (IIS, SQL Server Express, application services) recover cleanly when memory is freed?

  • Autoscaling: Does a memory-based scaling policy fire and add capacity?

  • Monitoring SLA: Does the alert on Memory % Committed Bytes In Use fire within the SLA?

  • Recovery time: When the chaos ends, how quickly does memory return to baseline?

Prerequisites

  • Kubernetes version: 1.21 or later for the chaos infrastructure cluster. Go to What's supported to confirm distribution support.

  • Target Windows EC2 instances: Each instance is in the running state and registered with AWS Systems Manager.

  • Selection criteria: Either EC2_INSTANCE_ID is set or EC2_INSTANCE_TAG is set.

  • AWS credentials available: Either an AWS credentials file uploaded as a File Secret in Harness Secret Manager (see Authentication below) or an IAM role for service accounts (IRSA) bound to the chaos infrastructure service account.

  • IAM permissions granted: The credentials or role include the permissions listed below.

Supported environments

Platform
Support status

Windows Server 2016 / 2019 / 2022 EC2

Supported

Linux EC2 instances

Not supported (use EC2 memory hog)

AWS regions

Supported in every commercial region; pass the region in REGION

Permissions required

The IAM principal that the chaos pod uses (the credentials mounted from the Harness Secret Manager file secret, the IRSA role on the chaos service account, or the role assumed via ASSUME_ROLE_ARN) needs the following AWS actions.

Go to common policy for all AWS faults to use a single superset IAM policy across every AWS fault.

Authentication

The fault supports three credential delivery models. Pick one based on how your chaos infrastructure is deployed.

Method
When to use it
How to configure

Harness Secret Manager file secret

Chaos infrastructure runs outside EKS, or you want explicit static credentials

Upload the AWS credentials file as a File Secret in Harness Secret Manager and reference its identifier via AWS_AUTHENTICATION_SECRET

IAM Roles for Service Accounts (IRSA)

Chaos infrastructure runs in EKS and uses an OIDC-bound service account

No tunable changes; the chaos pod inherits the role automatically. Go to AWS IAM integration to set it up

Assume role

The fault needs to act in a different account or with elevated permissions

Set ASSUME_ROLE_ARN to the role ARN; the chaos pod assumes the role on top of its base credentials

When using the Harness Secret Manager method, the contents of the File Secret should be the AWS credentials file in the standard ~/.aws/credentials format:

Upload this file as a File Secret in Harness Secret Manager (Project Setup → Secrets → New File Secret), and pass the secret identifier in AWS_AUTHENTICATION_SECRET when configuring the fault.

Go to AWS named profile for chaos to switch between profiles inside a single credentials file.

Fault tunables

Configure the following fault parameters when you add Windows EC2 memory hog to an experiment in Chaos Studio. Defaults are shown for reference.

Required parameters

Tunable
Description
Default

REGION

AWS region that hosts the target instances (for example us-east-1).

(required)

Targeting parameters

Tunable
Description
Default

EC2_INSTANCE_ID

Comma-separated list of EC2 instance IDs to affect.

""

EC2_INSTANCE_TAG

Tag in Key:Value form matching candidate instances when EC2_INSTANCE_ID is empty.

""

INSTANCE_AFFECTED_PERC

Percentage of matching instances (by tag) to affect. 0 corresponds to one instance.

0

Chaos parameters

Tunable
Description
Default

MEMORY_CONSUMPTION

Memory to allocate in MB. Set to 0 and use MEMORY_PERCENTAGE for percentage-based allocation.

0

MEMORY_PERCENTAGE

Percentage of total system memory to allocate. Used only when MEMORY_CONSUMPTION=0.

50

TOTAL_CHAOS_DURATION

Duration of the fault in seconds.

60

INSTALL_DEPENDENCIES

Install the stress tooling on the Windows host if missing.

true

SEQUENCE

Order in which multiple instances are stressed: parallel stresses all selected instances at once; serial stresses one at a time.

parallel

RAMP_TIME

Wait period in seconds before and after the fault. Go to ramp time to read how it is applied.

0

Authentication

Tunable
Description
Default

ASSUME_ROLE_ARN

ARN of an IAM role to assume on top of the base credentials. Leave empty to use the base credentials directly.

""

AWS_AUTHENTICATION_SECRET

Identifier of the File Secret in Harness Secret Manager that contains the AWS credentials file. Not required when using IRSA.

""

Tunables that apply to every fault are documented in common tunables for all faults. AWS-specific shared tunables are documented in common AWS fault tunables.

Fault execution in brief

Resolves the target instance list from EC2_INSTANCE_ID (or by EC2_INSTANCE_TAG), dispatches a PowerShell memory-allocation command via AWS Systems Manager Run Command to each selected Windows instance, holds the allocation for TOTAL_CHAOS_DURATION seconds, then releases the memory.

Expected behavior during fault execution

  • Free memory on the targeted Windows instances drops by approximately MEMORY_CONSUMPTION MB (or to the MEMORY_PERCENTAGE target).

  • If the working set exceeds available physical memory, Windows pages to the paging file; throughput collapses.

  • IIS and Windows services may experience increased response latency.

  • CloudWatch MemoryUtilization (when the CloudWatch Agent is installed) rises.

WHEN THE FAULT ENDS

The chaos pod releases the memory on each host. Memory returns to baseline within seconds.

Signals to watch

Attach resilience probes to assert each layer:

  • Memory utilization: Use a Prometheus probe on a memory-utilization metric (Memory % Committed Bytes In Use exported via CloudWatch).

  • Application latency: Use an HTTP probe and assert percentile latency SLOs.

  • Paging activity: Use a Prometheus probe on Pages/sec or equivalent to detect pressure.

  • Service availability: Monitor that Windows services stay in the Running state.

Verify the fault execution effect

While the experiment is running, confirm memory pressure is applied:

  1. Inspect from the Windows host (via SSM Session Manager).

    Available memory should drop by approximately MEMORY_CONSUMPTION during the chaos window.

  2. Check CloudWatch (if the CW Agent is installed).

    In CloudWatch, mem_used_percent (or the equivalent) should rise on the affected instances.

  3. Inspect SSM command status.

Recovery and cleanup

  • End of duration: The chaos pod releases the memory on each host.

  • Abort the experiment: Stopping the experiment from Chaos Studio cancels the SSM command.

  • Manual recovery: If the fault exits before cleanup, kill the stress process on the host via SSM Run Command (PowerShell Stop-Process).

  • Workload recovery: Pages swapped out during the stress are read back into memory on demand; some latency may persist briefly after recovery.

Limitations

  • Windows-only.

  • SSM-managed hosts only.

  • Paging file behaviour: If the paging file is small or disabled, Windows may BSOD or kill processes when memory is exhausted.

  • Cross-region targeting: A single experiment targets one region (the value of REGION).

Troubleshooting

Windows EC2 memory hog fails with AccessDeniedException in Harness Chaos Engineering

The credentials supplied to the chaos pod do not have the required EC2 or SSM permissions. Confirm the IAM policy attached to the user, role, or IRSA service account includes ec2:DescribeInstances, ssm:SendCommand, ssm:GetCommandInvocation, and the ec2messages:* actions used by SSM.

Windows EC2 memory hog reports instance is not SSM-managed

Confirm the SSM Agent is installed and running on the Windows host (the SSMAgent service should be in Running state), the host has an instance profile with AmazonSSMManagedInstanceCore (or equivalent), and the host appears in 'aws ssm describe-instance-information' with PlatformType=Windows.

System becomes unresponsive during the chaos window

If MEMORY_PERCENTAGE is very high (90+) and the paging file is small, Windows may freeze or BSOD as it runs out of memory. Lower MEMORY_PERCENTAGE to a value that leaves headroom (60-70 is usually safe), and ensure the paging file is sized appropriately for the workload.

Memory utilization does not rise during the chaos window

The most common causes are: the chaos process exited early (check the SSM command output); MEMORY_CONSUMPTION is small relative to total memory (raise it); or the host has more physical memory than expected. Check Get-Counter '\\Memory\\Available MBytes' on the host to confirm.

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