Fix DNS resolution performance regression during cloud-init local

[drzee99]

Fix DNS resolution performance regression during cloud-init local

Summary

This PR addresses critical DNS resolution performance issues during the early cloud-init local stage that cause boot delays of 2+ minutes, particularly with systemd version 259 and later.

Problem

• Boot delays: 2+ minutes (up from <30 seconds) during cloud-init local
• Root cause: DNS queries for IP addresses during DNS redirect detection
• Systemd 259 regression: Recent systemd changes make DNS resolution significantly slower during early boot
• Legacy URL: Hardcoded DNS-dependent metadata URL that's no longer documented by AWS

Solution

1. Optimize IP address handling in util.py

• Move IP address detection to function start to bypass all DNS operations
• Remove duplicate IP check that occurred after expensive DNS queries
• IP addresses now completely avoid DNS redirect detection

2. Remove legacy DNS-dependent URL from DataSourceEc2.py

• Remove http://instance-data.:8773 which is not in current AWS IMDS documentation
• Keep only IP-based endpoints that work without DNS resolution

Changes

• cloudinit/util.py: Early return for IP addresses in is_resolvable()
• cloudinit/sources/DataSourceEc2.py: Remove legacy DNS-dependent metadata URL

Testing

• IP addresses return immediately from is_resolvable()
• Cloud-init local completes in <30 seconds (down from 2+ minutes)
• IMDS access works without DNS resolution
• No functional regressions

Related Issues

Fixes #6641 - Systemd version 259 slows down DNS check during cloud-init local

Backward Compatibility

• ✅ No breaking changes
• ✅ Maintains all existing functionality
• ✅ Uses only documented AWS IMDS endpoints

[holmanb]

Thanks for the contribution. Please make sure that you have read the contribution guide.

[holmanb]

The ec2 datasource is used by various other clouds besides just ec2 - and unfortunately not all clouds are known, so this change poses a risk.

[drzee99]

That is confusing. There should be a separate Data Source implementation for each provider. Even if some are same/similar to allow for future changes a cloud provider may implement.

That being said.

It is possible to override the metadata_urls ref: https://cloudinit.readthedocs.io/en/latest/reference/datasources/ec2.html

IMHO the default should be the ones that are provided by the named Data Source (in this case EC2). If this breaks other cloud providers that use the same path, then they should create an config setting for the metadata_url as pr. documentation to add the relevant metadata_urls.

[drzee99]

I have approved the CLA.