AWS peer discovery: ensure consistent hostname path ordering

[BenAtAmazon]

Proposed Changes

AWS EC2 API returns networkInterfaceSet and privateIpAddressesSet in arbitrary order, causing non-deterministic hostname resolution during peer discovery and inconsistent cluster formation when setting certain cluster_formation.aws.hostname_path configurations such as:

cluster_formation.aws.hostname_path = networkInterfaceSet,2,privateIpAddressesSet,1,privateIpAddress

See https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DescribeInstances.html

"The order of the elements in the response, including those within nested structures, might vary. Applications should not assume the elements appear in a particular order."

Changes:

• Sort network interfaces by deviceIndex (0 first for primary ENI)
• Sort private IP addresses by primary flag (primary=true first)
• Add debug logging to show hostname path selection and sorting results (removed in second revision)
• Add unit tests for sorting behavior

The sorting ensures deviceIndex=0 and primary=true IPs are consistently selected as intended, making peer discovery deterministic across deployments. Note that since EC2 does not provide an index for privateIpAddressesSet (like deviceIndex for networkInterfaceSet), this determinism for privateIpAddressesSet only applies if there are 1 or 2 members in privateIpAddressesSet via the primary=true or primary=false. If there was a 3rd member in privateIpAddressesSet, the two primary=false IPs orders are non-deterministic.

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Further Comments

N/A

[SimonUnge]

Looks good to me!