From 7c2e9e5fc8abdafe3efbae6a46a431cebf26f54b Mon Sep 17 00:00:00 2001
From: MickLesk <47820557+MickLesk@users.noreply.github.com>
Date: Wed, 11 Nov 2026 20:39:03 +0100
Subject: [PATCH] Fall back to public DNS for Alpine containers too

The Debian branch checks name resolution before apt-get update and
writes public resolvers when it fails. The Alpine branch went straight
to apk, and its mirror fallback only tries other host names, so a dead
resolver failed every mirror: 73 installs in a week ended in "Failed to
install base packages in Alpine container" behind "DNS: transient
error". Same check now on Proxmox VE and Incus.
---
 incus/backend.func | 4 ++++
 pve/backend.func   | 5 +++++
 2 files changed, 9 insertions(+)

diff --git a/incus/backend.func b/incus/backend.func
index 70a25c9..e468e36 100644
--- a/incus/backend.func
+++ b/incus/backend.func
@@ -1037,6 +1037,10 @@ incus_customize_container() {
 http://dl-cdn.alpinelinux.org/alpine/${alpine_rel}/main
 http://dl-cdn.alpinelinux.org/alpine/${alpine_rel}/community
 EOF"
+    if ! incus_ct_exec /bin/sh -c 'getent hosts dl-cdn.alpinelinux.org >/dev/null 2>&1'; then
+      msg_warn "Alpine repository DNS resolution failed in container, injecting public DNS servers"
+      incus_ct_exec /bin/sh -c 'printf "nameserver 8.8.8.8\nnameserver 1.1.1.1\n" >/etc/resolv.conf'
+    fi
     incus_ct_exec ash -c "apk add bash newt curl openssh nano mc ncurses jq >/dev/null" || msg_warn "Alpine base package install had issues"
   elif [[ "${var_os:-debian}" =~ ^(debian|ubuntu|devuan)$ ]]; then
     sleep 2
diff --git a/pve/backend.func b/pve/backend.func
index da4bd73..a958fd0 100644
--- a/pve/backend.func
+++ b/pve/backend.func
@@ -1192,6 +1192,11 @@ EOF
 https://dl-cdn.alpinelinux.org/alpine/latest-stable/main
 https://dl-cdn.alpinelinux.org/alpine/latest-stable/community
 EOF'
+   # As for Debian below: with a dead resolver every mirror fails alike.
+   if ! pct exec "$CTID" -- /bin/sh -c 'getent hosts dl-cdn.alpinelinux.org >/dev/null 2>&1'; then
+     msg_warn "Alpine repository DNS resolution failed in container, injecting public DNS servers"
+     pct exec "$CTID" -- /bin/sh -c 'printf "nameserver 8.8.8.8\nnameserver 1.1.1.1\n" >/etc/resolv.conf'
+   fi
    _cs_shield_hangup pct exec "$CTID" -- ash -c 'set -a; [ -f /etc/profile.d/90-http-proxy.sh ] && . /etc/profile.d/90-http-proxy.sh; set +a; apk add bash newt curl openssh nano mc ncurses jq' >>"$BUILD_LOG" 2>&1 || {
      msg_warn "apk install failed (dl-cdn.alpinelinux.org), trying alternate mirrors..."
      local alpine_exit=0