fix(aws-ssi): retry stack up in-process on InsufficientInstanceCapacity

[cbeauchesne]

Motivation

Several AWS SSI jobs fail on EC2 capacity errors, e.g. in pipeline 144379440:

creating EC2 Instance: InsufficientInstanceCapacity: We currently do not have sufficient t4g.medium capacity
in the Availability Zone you requested (us-east-1c). [...] You can currently get t4g.medium capacity by [...]
choosing us-east-1a, us-east-1b, us-east-1d, us-east-1f.

This error was neither retried in-process (only IdempotentParameterMismatch was) nor listed in the known infra exceptions. So the job failed with exit code 1, and GitLab never retried it.

Changes

• _stack_up_with_idempotency_retry is renamed to _stack_up_with_retry. It also retries on InsufficientInstanceCapacity: it excludes the subnet that failed, destroys the stack, waits 30s, then runs the stack up again on another subnet (3 attempts in total, same as before).
• The new _pick_subnet_id picks randomly among subnets that haven't failed yet. If all of them have failed, it picks among all subnets.
• InsufficientInstanceCapacity is added to aws_infra_exceptions.json, so if every attempt fails the job exits with code 3 and GitLab retries it.

Note: a retry only reaches another AZ if the subnets in ONBOARDING_AWS_INFRA_SUBNET_ID are in different AZs.

Workflow

1. ⚠️ Create your PR as draft ⚠️
2. Work on you PR until the CI passes
3. Mark it as ready for review
   • Tests, manifest, weblog are modified -> you'll need a review from system-tests-reviewers: ask to one of youre co-worker familiar with the tested feature.
   • Framework is modified, or non obvious usage of it -> get a review from system-tests-core (slack)

🚀 Once your PR is reviewed and the CI green, you can merge it!

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🤖 Generated with Claude Code

[github-actions]

CODEOWNERS have been resolved as:

utils/virtual_machine/aws_infra_exceptions.json                         @DataDog/system-tests-core
utils/virtual_machine/aws_provider.py                                   @DataDog/system-tests-core

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-14T09:07:52.986632Z	3344574	Draft marked ready

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