fix: Add IPv6 IMDS support for IPv6-only subnets#70
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dpakpak merged 1 commit intoaws:masterfrom Mar 7, 2026
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The IMDS base URL was hardcoded to the IPv4 link-local address (169.254.169.254), causing instance initialization to fail on IPv6-only networks. SSH key injection and metadata retrieval would silently fail since the endpoint was unreachable. Resolve the IMDS endpoint at runtime by trying IPv4 first and falling back to the IPv6 endpoint (fd00:ec2::254). Also support the EC2_METADATA_SERVICE_ENDPOINT_MODE environment variable for explicit override, consistent with the AWS SDK convention.
jahkeup
approved these changes
Mar 6, 2026
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| // Neither endpoint confirmed reachable yet — return IPv4 default | ||
| // without caching so we re-probe on the next call. | ||
| return imdsIPv4Base |
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Nice! Thanks for handling the retry loop gracefully 🌮
mjbala
approved these changes
Mar 6, 2026
mattcataws
approved these changes
Mar 6, 2026
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Problem
macOS instances launched in IPv6-only subnets fail to initialize. SSH key injection,
metadata retrieval, and all IMDS-dependent operations silently fail because the IMDS
base URL is hardcoded to the IPv4 link-local address (
169.254.169.254), which isunreachable in IPv6-only networks.
Solution
Replace the hardcoded IMDS base URL with runtime endpoint resolution:
169.254.169.254) and IPv6 (fd00:ec2::254)EC2_METADATA_SERVICE_ENDPOINT_MODE(
ipv4|ipv6), consistent with the AWS SDK conventionendpoint is reachable, preserving the existing retry loop behavior
Behavior
Testing
mac2.metalwith IMDS disabled: init retries correctly, recoverswhen IMDS re-enabled, no crash or panic
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