[amogh09]

Summary

This change fixes a bug in agent update (UpdateContainerAgent API) handling for IPv6-only instances. The update location (S3 URL) streamed down to Agent is currently not IPv6 compatible, so as a temporary workaround, Agent needs to convert it to IPv6-only compatible (dualstack) S3 URL.

Legacy S3 URLs have format -

s3.<aws-region>.<partition-suffix>/bucketname

Dualstack S3 URLs have format -

s3.dualstack.<aws-region>.<partition-suffix>/bucketname

so, the conversion is rather simple and works for all partitions.

Testing

I made some temporary changes to make Agent think that it's running v1.98.0 with its corresponding build ID. Then I ran that Agent on an IPv6-only instance and called UpdateContainerAgentAPI on it. Update was successful.

Agent logs -

level=info time=2025-09-16T16:21:38Z msg="Starting Amazon ECS Agent" version="1.98.0" commit="7d5ec06f"
...
level=debug time=2025-09-16T16:22:05Z msg="Staging updateupdate{\n  ClusterArn: \"arn:aws:ecs:us-west-2:979604884904:cluster/default\",\n  ContainerInstanceArn: \"arn:aws:ecs:us-west-2:979604884904:container-instance/default/d8d3da61c4504e67bdfbf298f5e5bd79\",\n  MessageId: \"14def9e9-de8f-4654-8a9d-f0ef9867e870\",\n  UpdateInfo: {\n    Location: \"https://s3.us-west-2.amazonaws.com/amazon-ecs-agent-us-west-2/ecs-agent-v1.99.0.tar\",\n    Signature: \"d884c06823f46705f065d3c89b351295c07a6ca85d8cc1155a97bc162eae59c5\"\n  }\n}" module=updater.go
level=info time=2025-09-16T16:22:05Z msg="Converting agent update URL to dual-stack for IPv6" originalURL="https://s3.us-west-2.amazonaws.com/amazon-ecs-agent-us-west-2/ecs-agent-v1.99.0.tar" dualStackURL="https://s3.dualstack.us-west-2.amazonaws.com/amazon-ecs-agent-us-west-2/ecs-agent-v1.99.0.tar"
...
level=debug time=2025-09-16T16:22:13Z msg="Got perform update request" module=updater.go
level=debug time=2025-09-16T16:22:13Z msg="Shutting down task engine for final save" module=termination_handler.go
level=debug time=2025-09-16T16:22:13Z msg="Saving state before shutting down" module=termination_handler.go
level=info time=2025-09-16T16:22:13Z msg="Starting Amazon ECS Agent" version="1.99.0" commit="ad700257"

Introspection before/after -

[ec2-user@i-0859029921f52268e ~]$ curl -s http://localhost:51678/v1/metadata | python3 -mjson.tool
{
    "Cluster": "default",
    "ContainerInstanceArn": "arn:aws:ecs:us-west-2:979604884904:container-instance/default/d8d3da61c4504e67bdfbf298f5e5bd79",
    "Version": "Amazon ECS Agent - v1.98.0 (*7d5ec06f)"
}
[ec2-user@i-0859029921f52268e ~]$ curl -s http://localhost:51678/v1/metadata | python3 -mjson.tool
{
    "Cluster": "default",
    "ContainerInstanceArn": "arn:aws:ecs:us-west-2:979604884904:container-instance/default/d8d3da61c4504e67bdfbf298f5e5bd79",
    "Version": "Amazon ECS Agent - v1.99.0 (*ad700257)"
}

New tests cover the changes: yes

Description for the changelog

bugfix: Fix agent update handling for IPv6-only instances

Additional Information

Does this PR include breaking model changes? If so, Have you added transformation functions?

Does this PR include the addition of new environment variables in the README?

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.