fix: make nginx configuration reload transactional

nginx/.reload-in-container.sh

@@ -0,0 +1,130 @@
+#!/bin/sh
+
+set -eu
+
+# Share template paths with the Nginx image's envsubst entrypoint.
+readonly TEMPLATE_DIR="${NGINX_ENVSUBST_TEMPLATE_DIR:-/etc/nginx/templates}"
+readonly TEMPLATE_SUFFIX="${NGINX_ENVSUBST_TEMPLATE_SUFFIX:-.template}"
+readonly OUTPUT_DIR="${NGINX_ENVSUBST_OUTPUT_DIR:-/etc/nginx}"
+readonly ENVSUBST_SCRIPT="${NGINX_RELOAD_ENVSUBST_SCRIPT:-/docker-entrypoint.d/20-envsubst-on-templates.sh}"
+readonly MANAGED_DIRS="conf.d snippets"
+
+is_managed_template() {
+	for managed_dir in $MANAGED_DIRS; do
+		case "$1" in
+		"$managed_dir"/*) return 0 ;;
+		esac
+	done
+	return 1
+}
+
+validate_templates() {
+	if [ ! -d "$TEMPLATE_DIR" ]; then
+		echo "Error: template directory does not exist: $TEMPLATE_DIR" >&2
+		return 1
+	fi
+
+	if [ ! -x "$ENVSUBST_SCRIPT" ]; then
+		echo "Error: envsubst script is not executable: $ENVSUBST_SCRIPT" >&2
+		return 1
+	fi
+
+	# Collect first so a failed find cannot be masked by a pipeline.
+	templates="$(find "$TEMPLATE_DIR" -follow -type f -name "*$TEMPLATE_SUFFIX" -print)"
+	printf '%s\n' "$templates" | while IFS= read -r template; do
+		[ -n "$template" ] || continue
+		relative="${template#"$TEMPLATE_DIR"/}"
+		if ! is_managed_template "$relative"; then
+			echo "Error: unmanaged template path: $relative" >&2
+			exit 1
+		fi
+	done
+}
+
+backup_config() {
+	for dir in $MANAGED_DIRS; do
+		if [ -d "$OUTPUT_DIR/$dir" ]; then
+			cp -a "$OUTPUT_DIR/$dir" "$1/$dir"
+		fi
+	done
+}
+
+generate_config() {
+	for dir in $MANAGED_DIRS; do
+		if [ -d "$OUTPUT_DIR/$dir" ]; then
+			outputs="$(find "$OUTPUT_DIR/$dir" -type f -print)"
+			printf '%s\n' "$outputs" | while IFS= read -r output; do
+				[ -n "$output" ] || continue
+				relative="${output#"$OUTPUT_DIR"/}"
+				if [ ! -f "$TEMPLATE_DIR/$relative$TEMPLATE_SUFFIX" ]; then
+					echo "Removing stale generated file: $relative"
+				fi
+			done
+		fi
+
+		rm -rf "$OUTPUT_DIR/$dir"
+		mkdir -p "$OUTPUT_DIR/$dir"
+	done
+	NGINX_ENVSUBST_TEMPLATE_DIR="$TEMPLATE_DIR" \
+		NGINX_ENVSUBST_TEMPLATE_SUFFIX="$TEMPLATE_SUFFIX" \
+		NGINX_ENVSUBST_OUTPUT_DIR="$OUTPUT_DIR" \
+		"$ENVSUBST_SCRIPT"
+}
+
+restore_config() {
+	restore_failed=0
+	for dir in $MANAGED_DIRS; do
+		if ! rm -rf "$OUTPUT_DIR/$dir"; then
+			restore_failed=1
+			continue
+		fi
+		if [ -d "$1/$dir" ]; then
+			cp -a "$1/$dir" "$OUTPUT_DIR/$dir" || restore_failed=1
+		fi
+	done
+	[ "$restore_failed" -eq 0 ]
+}
+
+finish() {
+	finish_status="$1"
+	trap - EXIT
+	trap '' HUP INT TERM
+
+	if [ "$2" = modifying ]; then
+		echo "Reload failed. Restoring previous generated configuration." >&2
+		[ "$finish_status" -ne 0 ] || finish_status=1
+		if ! restore_config "$3"; then
+			echo "Error: configuration rollback incomplete. Backup preserved at: $3" >&2
+			exit "$finish_status"
+		fi
+	fi
+
+	if ! rm -rf "$3"; then
+		echo "Error: cannot remove configuration backup: $3" >&2
+		[ "$finish_status" -ne 0 ] || finish_status=1
+	fi
+	if [ "$finish_status" -eq 0 ] && [ "$2" = committed ]; then
+		echo "Nginx configuration reloaded successfully."
+	fi
+	exit "$finish_status"
+}
+
+main() {
+	validate_templates
+	backup_dir="$(mktemp -d /tmp/nginx-reload.XXXXXX)"
+	transaction_state=backing_up
+	trap 'finish "$?" "$transaction_state" "$backup_dir"' EXIT
+	trap 'exit 129' HUP
+	trap 'exit 130' INT
+	trap 'exit 143' TERM
+
+	backup_config "$backup_dir"
+	# Only a complete backup permits mutation and subsequent restoration.
+	transaction_state=modifying
+	generate_config
+	nginx -t
+	nginx -s reload
+	transaction_state=committed
+}
+
+main "$@"

nginx/reload.sh

@@ -1,102 +1,7 @@
 #!/usr/bin/env bash
 
-set -Eeuo pipefail
+set -euo pipefail
 
 cd -- "$(dirname -- "${BASH_SOURCE[0]}")"
 
-readonly SERVICE="nginx"
+exec docker compose exec -T nginx sh -s <./.reload-in-container.sh
-
-if ! docker compose exec -T "$SERVICE" true >/dev/null 2>&1; then
-	echo "Error: nginx container is not running." >&2
-	exit 1
-fi
-
-docker compose exec -T "$SERVICE" sh <<'EOF'
-set -eu
-
-TEMPLATE_DIR="/etc/nginx/templates"
-OUTPUT_DIR="/etc/nginx"
-ENVSUBST_SCRIPT="/docker-entrypoint.d/20-envsubst-on-templates.sh"
-MANAGED_DIRS="conf.d snippets"
-
-if [ ! -d "$TEMPLATE_DIR" ]; then
-	echo "Error: template directory does not exist: $TEMPLATE_DIR" >&2
-	exit 1
-fi
-
-if [ ! -x "$ENVSUBST_SCRIPT" ]; then
-	echo "Error: envsubst script is not executable: $ENVSUBST_SCRIPT" >&2
-	exit 1
-fi
-
-# Only allow templates in directories managed by this script.
-find "$TEMPLATE_DIR" -type f -name '*.template' -print | while IFS= read -r template; do
-	relative="${template#"$TEMPLATE_DIR"/}"
-
-	case "$relative" in
-	conf.d/* | snippets/*)
-		;;
-	*)
-		echo "Error: unmanaged template path: $relative" >&2
-		exit 1
-		;;
-	esac
-done
-
-backup_dir="$(mktemp -d /tmp/nginx-reload.XXXXXX)"
-committed=0
-
-rollback() {
-	status=$?
-
-	if [ "$committed" -eq 0 ]; then
-		echo "Reload failed. Restoring previous generated configuration." >&2
-
-		for dir in $MANAGED_DIRS; do
-			rm -rf "$OUTPUT_DIR/$dir"
-
-			if [ -d "$backup_dir/$dir" ]; then
-				cp -a "$backup_dir/$dir" "$OUTPUT_DIR/$dir"
-			fi
-		done
-	fi
-
-	rm -rf "$backup_dir"
-	exit "$status"
-}
-
-trap rollback EXIT HUP INT TERM
-
-for dir in $MANAGED_DIRS; do
-	if [ -d "$OUTPUT_DIR/$dir" ]; then
-		cp -a "$OUTPUT_DIR/$dir" "$backup_dir/$dir"
-	fi
-done
-
-for dir in $MANAGED_DIRS; do
-	if [ -d "$OUTPUT_DIR/$dir" ]; then
-		find "$OUTPUT_DIR/$dir" -type f -print | while IFS= read -r output; do
-			relative="${output#"$OUTPUT_DIR"/}"
-
-			if [ ! -f "$TEMPLATE_DIR/$relative.template" ]; then
-				echo "Removing stale generated file: $relative"
-			fi
-		done
-	fi
-
-	rm -rf "$OUTPUT_DIR/$dir"
-	mkdir -p "$OUTPUT_DIR/$dir"
-done
-
-"$ENVSUBST_SCRIPT"
-
-nginx -t
-
-committed=1
-trap - EXIT HUP INT TERM
-rm -rf "$backup_dir"
-EOF
-
-docker compose exec -T "$SERVICE" nginx -s reload
-
-echo "Nginx configuration reloaded successfully."