feat: add DNS pre-flight check to verify Docker connectivity before s… (#398)

* feat: add DNS pre-flight check to verify Docker connectivity before startup

* feat: implement exponential backoff and improved status reporting for Docker DNS pre-flight checks

Author: YashIIT0909

scripts/start

@@ -19,6 +19,45 @@ if [ "$EUID" -eq 0 ]
   exit 1
 fi
 
+# ── DNS Pre-flight Check ─────────────────────────────────────────────
+YELLOW=$'\033[0;33m'
+BOLD_YELLOW=$'\033[1;33m'
+NC=$'\033[0m'
+DNS_TEST_URL="https://dl-cdn.alpinelinux.org"
+DNS_MAX_RETRIES=3
+DNS_OK=false
+BACKOFF=2
+
+echo "Checking Docker DNS connectivity..."
+for i in $(seq 1 $DNS_MAX_RETRIES); do
+  printf "  [Attempt $i/$DNS_MAX_RETRIES] Testing resolution... "
+  if docker run --rm alpine wget --spider --timeout=5 "$DNS_TEST_URL" > /dev/null 2>&1; then
+    echo "Success"
+    DNS_OK=true
+    break
+  else
+    echo "Failed"
+  fi
+  [ "$i" -lt "$DNS_MAX_RETRIES" ] && sleep $BACKOFF && BACKOFF=$((BACKOFF * 2))
+done
+
+if [ "$DNS_OK" = false ]; then
+  cat <<EOF >&2
+
+${BOLD_YELLOW}  WARNING: Docker DNS resolution failed after $DNS_MAX_RETRIES attempts.${NC}
+${YELLOW}   Containers cannot resolve external domains (e.g. dl-cdn.alpinelinux.org).
+   This is commonly caused by a DNS bridge conflict with systemd-resolved.
+
+   Suggested fixes:
+     1. Add DNS to /etc/docker/daemon.json:
+        { "dns": ["8.8.8.8", "8.8.4.4"] }
+     2. Then run sudo systemctl restart docker
+
+   The build will continue, but may fail during package installation.${NC}
+
+EOF
+fi
+
 if [[ ! -d "${NOSTR_CONFIG_DIR}" ]]; then
   echo "Creating folder ${NOSTR_CONFIG_DIR}"
   mkdir -p "${NOSTR_CONFIG_DIR}"