"aws cloudwatch list-metrics" runs forever when ran on an ipv6 only box

[paul-civitas]

Describe the bug

When you run: aws ecr get-login-password from an ipv6 machine, it eventually times out as it can't establish a connection to ecr with the default endpoint (as you're required to use the dualstack endpoint, which has a separate address).

However when you run aws cloudwatch list-metrics from an ipv6 machine the command hangs indefinitely, which suggests a missing timeout in the codebase.

Regression Issue

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

Expected Behavior

Either it works successfully or it times out.

Current Behavior

Program does not halt.

Reproduction Steps

Spin up a ipv6 only ec2 box.

Observe that aws secretsmanager list-secrets works correctly (as its default endpoint supports ipv6).

Observe that aws ecr get-login-password times out after some number of minutes.

Observe that aws cloudwatch list-metrics --debug runs seemingly indefinitely.

Possible Solution

Fix your timeouts ideally. But of course I'd love if aws's ipv6 support was improved as well of course.

Additional Information/Context

Spinning up ipv6 only boxes these days is actually quite easy.

CLI version used

aws-cli/2.25.0 Python/3.13.3 Linux/6.14.6-300.fc42.aarch64 source/aarch64.fedora.42

Environment details (OS name and version, etc.)

Fedora on us-east-2

[adev-code]

Hello @paul-civitas, thanks for reaching out. I have replicated the same environment where I only have IPv6 egress and got results.

• aws secretsmanager list-secrets - either UseDualStack': True or UseDualStack': False , the command works.
• aws cloudwatch list-metrics --debug - in order to use IPv6, you would need to set UseDualStack': True (e.g. running the command: aws configure set use_dualstack_endpoint true) https://docs.aws.amazon.com/cli/v1/userguide/cli-configure-endpoints.html#endpoints-dual-stack
• aws ecr get-login-password - neither UseDualStack': True or UseDualStack': False does not work.

Each services have their own implementation of supporting IPv6. I have reached out to the ECR Service team to see if ECR supports IPv6. I will update back if there's any updates. If you have any questions, please do let me know. Thank you.

For Internal Tracking: P250001544

[adev-code]

Hi @paul-civitas, also please ensure that you are using an AWS CLI version from 2.27.5 https://raw.githubusercontent.com/aws/aws-cli/v2/CHANGELOG.rst and from that, you can enable dual stack in order to connect to ECR via IPv6. If you have any questions, please do let me know. Thank you.

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