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fix(lib): write drop-in configs to active network file directory #147

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fix(lib): write drop-in configs to active network file directory #147

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fix(lib): write drop-in configs to active network file directory
mjnowen Mar 30, 2026
f5ab0c2
add .gitignore
mjnowen Apr 1, 2026
710d5ed
Merge branch 'amazonlinux:main' into fix/dropin-dir-follows-active-ne…
mjnowen May 29, 2026
465cdb1
Merge branch 'main' into fix/dropin-dir-follows-active-network-file
mjnowen May 29, 2026
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Merge branch 'amazonlinux:main' into fix/dropin-dir-follows-active-ne…
mjnowen May 29, 2026
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Merge branch 'main' into fix/dropin-dir-follows-active-network-file
mjnowen May 29, 2026
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Merge branch 'main' into add-gitignore
mjnowen May 29, 2026
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Merge branch 'add-gitignore' into fix/dropin-dir-follows-active-netwo…
mjnowen May 29, 2026
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Merge remote-tracking branch 'fork/fix/dropin-dir-follows-active-netw…
mjnowen May 29, 2026
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13 changes: 13 additions & 0 deletions .gitignore
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Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
# Dev Container
/.devcontainer/

# VS Code
.vscode
*.code-workspace

# IDE
.cursor
.kiro

# Miscellaneous files
*.DS_Store
19 changes: 17 additions & 2 deletions lib/lib.sh
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Expand Up @@ -233,13 +233,27 @@ _install_and_reload() {
fi
}

_get_active_dropin_dir() {
local iface=$1
local default_dir="${unitdir}/70-${iface}.network.d"
local ifindex network_file
ifindex=$(cat "/sys/class/net/${iface}/ifindex" 2> /dev/null) || { echo "$default_dir"; return; }
network_file=$(sed -n 's/^NETWORK_FILE=//p' "/run/systemd/netif/links/${ifindex}" 2> /dev/null) || { echo "$default_dir"; return; }
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@joeysk2012 joeysk2012 Apr 1, 2026

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Could there be a race condition between netplan and ec2-net-utils during a restart where netplan config is not first and you have two seperate configs since netplan has not logic to append to ec2-net-utils config?

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@mjnowen mjnowen Apr 1, 2026 •
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The policy-routes@.service start path calls systemd-networkd-wait-online -i $iface before _get_active_dropin_dir() is ever invoked, so networkd has already selected its active .network file (including any netplan-generated one) by that time. The refresh path (timer-driven) does not call wait-online explicitly, but the timer only fires 30s+ after the start path completes (OnActiveSec=30, OnUnitInactiveSec=60), so the interface is already fully online and NETWORK_FILE= is populated.

On Ubuntu, netplan's systemd generator runs during the early generator phase — before any services start — so 10-netplan-*.network files are on disk well before systemd-networkd.service begins matching interfaces to files.

On Amazon Linux 2023 there is no competing generator — 70-<iface>.network is the only (and therefore active) file, so the helper returns the same path as the old hardcoded logic and no race is possible.

On RHEL the default network manager is NetworkManager rather than systemd-networkd, so this codepath does not apply.

If detection somehow fails (e.g. a truly degenerate early-boot ordering), the helper falls back to 70-<iface>.network.d — the same path used before this change — so the worst case is parity with the current behaviour, not a new failure mode.

The coexistence of 70-<iface>.network alongside a lower-numbered netplan file is pre-existing and unchanged by this PR; it's precisely that coexistence that causes the bug this fix addresses.

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@joeysk2012 joeysk2012 May 28, 2026

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This looks not like a distro-agnostic change. It assumses netplan will be used along with ec2-net-utils which AL23 does not. I would put it as a patch under the debian folder like we have done in the past. I just don't see carrying this extra logic comes with extra risk (even if it's small).

if [ -n "$network_file" ]; then
echo "${network_file}.d"
else
echo "$default_dir"
fi
}

create_ipv4_aliases() {
local iface=$1
local mac=$2
local addresses
subnet_supports_ipv4 "$iface" || return 0
addresses=$(get_iface_imds $mac local-ipv4s | tail -n +2 | sort)
local drop_in_dir="${unitdir}/70-${iface}.network.d"
local drop_in_dir
drop_in_dir=$(_get_active_dropin_dir "$iface")
mkdir -p "$drop_in_dir"
local file="$drop_in_dir/ec2net_alias.conf"
local work="${file}.new"
Expand Down Expand Up @@ -298,7 +312,8 @@ create_rules() {
local family=$4
local addrs prefixes
local local_addr_key subnet_pd_key
local drop_in_dir="${unitdir}/70-${iface}.network.d"
local drop_in_dir
drop_in_dir=$(_get_active_dropin_dir "$iface")
mkdir -p "$drop_in_dir"

local -i ruleid=$((device_number+rule_base+100*network_card))
Expand Down