Add isset guards to enable runtime variable overrides

[Skyrant]

Add isset guards to all iPXE variable assignments

Summary

This PR adds isset guards to all set commands across iPXE menu templates to enable runtime variable overrides via local-vars.ipxe without requiring a full rebuild. This change makes netboot.xyz more flexible for users who want to customize behavior (mirrors, timeouts, menu options) at boot time.

Motivation

Currently, most variables in boot.cfg.j2 and menu templates are set unconditionally, which means they cannot be overridden in local-vars.ipxe at runtime. Only a few variables (like live_endpoint and boot_timeout) already had isset guards. This inconsistency creates limitations for users who:

• Want to use custom/local mirrors for faster downloads
• Need to customize menu behavior without rebuilding
• Operate in air-gapped environments with local repositories
• Want to override cloud-specific settings dynamically

Changes Made

boot.cfg.j2

Added isset guards to all variable assignments:

• Global variables: site_name, boot_domain, memdisk, sigs_enabled, sigs, ipxe_disk
• Mirror loop: All dynamically generated ${distro}_mirror and ${distro}_base_dir variables
• Architecture flags: All menu_* variables across architecture sections (:architectures, :x86_64, :i386, :arm64, :efi)
• Cloud-specific settings: cmdline, ipxe_disk, and menu overrides in :gce, :metal_x86_64, :metal_arm64 sections

Individual Menu Templates

• tinycore.ipxe.j2: Added isset guard to tinycore_mirror
• k3os.ipxe.j2: Added isset guard to k3os_mirror
• debian.ipxe.j2:
  • Added isset guard to debian_mirror in :older_release section
  • Removed redundant no-op assignment set debian_mirror ${debian_mirror} with explanatory comment
• ubuntu.ipxe.j2: Added isset guard to ubuntu_mirror in :older_release section
• archlinux.ipxe.j2: Added comment clarifying that archlinux_mirror is already handled by boot.cfg.j2

Pattern Used

All changes follow the same idiomatic iPXE pattern:

isset ${variable} || set variable value

This ensures that if a variable is already set (e.g., in local-vars.ipxe which loads first), it won't be overwritten.

Boot Flow and Variable Loading

Problem: Without isset Guards

sequenceDiagram
    participant TFTP as TFTP Server
    participant LV as local-vars.ipxe
    participant BC as boot.cfg.j2
    participant Menu as Menu System
    
    TFTP->>LV: 1. Chain load
    Note over LV: set fedora_mirror http://my-mirror.lan
    Note over LV: ✓ Variable set by user
    
    LV->>BC: 2. Chain load
    Note over BC: set fedora_mirror {{ releases.fedora.mirror }}
    Note over BC: ❌ OVERWRITES user's mirror!
    
    BC->>Menu: 3. Boot menu
    Note over Menu: Uses default mirror<br/>User override ignored 😞

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Solution: With isset Guards

sequenceDiagram
    participant TFTP as TFTP Server
    participant LV as local-vars.ipxe
    participant BC as boot.cfg.j2
    participant Menu as Menu System
    
    TFTP->>LV: 1. Chain load
    Note over LV: set fedora_mirror http://my-mirror.lan
    Note over LV: ✓ Variable set by user
    
    LV->>BC: 2. Chain load
    Note over BC: isset ${fedora_mirror} ‖ set fedora_mirror ...
    Note over BC: ✓ Checks first, doesn't overwrite!
    
    BC->>Menu: 3. Boot menu
    Note over Menu: Uses user's mirror<br/>Override respected! 🎉

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Behavior

Before

Variables set in boot.cfg.j2 and menu templates would always overwrite any pre-existing values, making local-vars.ipxe overrides ineffective for most variables.

After

Users can now pre-set variables in local-vars.ipxe, and they will be respected throughout the boot process. For example:

# In local-vars.ipxe on TFTP server
set fedora_mirror http://my-local-mirror.lan/fedora
set boot_timeout 60000
set menu_windows 0

Testing

• ✅ Ansible syntax check passes: ansible-playbook site.yml --syntax-check
• ✅ All existing isset patterns maintained (live_endpoint, boot_timeout, etc.)
• ✅ No functional changes to default behavior (same defaults apply when variables not pre-set)
• ✅ Follows existing code style and iPXE best practices from AGENTS.md

Backwards Compatibility

Fully backwards compatible. When variables are not pre-set, they fall back to the same defaults as before. Existing deployments will see no change in behavior unless they explicitly leverage the new override capability.

Related

This addresses the inconsistency mentioned in local-vars.ipxe.j2 comments, where variables like rhel_base_url and win_base_url were documented as overridable, but many other variables were not.

Files Changed

• roles/netbootxyz/templates/menu/boot.cfg.j2 (108 lines changed)
• roles/netbootxyz/templates/menu/archlinux.ipxe.j2 (1 line added - comment)
• roles/netbootxyz/templates/menu/debian.ipxe.j2 (4 lines changed)
• roles/netbootxyz/templates/menu/k3os.ipxe.j2 (2 lines changed)
• roles/netbootxyz/templates/menu/tinycore.ipxe.j2 (2 lines changed)
• roles/netbootxyz/templates/menu/ubuntu.ipxe.j2 (2 lines changed)

Total: 60 insertions(+), 59 deletions(-)

[kilo-code-bot]

Code Review Summary

Status: No New Issues Found | Recommendation: Address Existing Comments

Overview

This review found no new issues beyond the 7 existing inline comments already posted. The changes consistently apply isset guards to enable runtime variable overrides, which aligns with the PR's stated goal.

Key Observations

✅ Consistent Pattern: All changes follow the idiomatic iPXE pattern isset ${var} || set var value

✅ Backwards Compatible: When variables are not pre-set, defaults are applied as before

✅ Debian Template Improvement: The removal of the redundant set debian_mirror ${debian_mirror} assignment (line 41) with an explanatory comment is a good cleanup

⚠️ Existing Issues: The 7 previously posted inline comments should be addressed, particularly:

• Jinja2 template syntax issues in the mirror loop (lines 35-36)
• Architecture and cloud-specific menu flag override concerns

Files Reviewed (2 files)

• roles/netbootxyz/templates/menu/boot.cfg.j2 - No new issues (existing comments apply)
• roles/netbootxyz/templates/menu/debian.ipxe.j2 - No issues

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Fix these issues in Kilo Cloud

[Copilot]

Pull request overview

This PR updates several netboot.xyz iPXE menu templates to make key variables (mirrors, global config, and some boot/menu flags) “override-friendly” by only setting defaults when variables are not already set.

Changes:

• Add isset ... || set ... guards for various mirrors and global variables to preserve externally-provided overrides.
• Adjust Debian/Ubuntu older-release handling and add clarifying comments about where mirrors are set.
• Add a small clarifying comment in the Arch Linux menu.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
roles/netbootxyz/templates/menu/boot.cfg.j2	Adds isset guards for global vars, per-release mirror/base_dir vars, arch/platform menu flags, and cloud/provider specifics.
roles/netbootxyz/templates/menu/debian.ipxe.j2	Uses isset guard when setting archive mirror for older releases; removes a self-assignment in :mirrorcfg and replaces with a comment.
roles/netbootxyz/templates/menu/ubuntu.ipxe.j2	Uses isset guard when setting archive mirror for older releases.
roles/netbootxyz/templates/menu/tinycore.ipxe.j2	Makes tinycore_mirror default-set only when unset.
roles/netbootxyz/templates/menu/k3os.ipxe.j2	Makes k3os_mirror default-set only when unset.
roles/netbootxyz/templates/menu/archlinux.ipxe.j2	Adds a comment about archlinux_mirror coming from boot.cfg.j2.

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[Skyrant]

fixed the issues, was a bit over-zealous with the isset changes.