【Go】App Engine Admin API を使って GAE サービスに dispatch_rules（送信ルート）を設定するサンプルコード

Go Cloud クライアントライブラリ の App Engine Admin API（cloud.google.com/go/appengine/apiv1） を使用して、App Engine の defaultサービスに dispatch_rules（送信ルート）を設定するサンプルコードです。

実行方法

PROJECT_ID=<GCのプロジェクトID> MODE=<ADD or DELETE> go run main.go 

サンプルコード

main.go

package main

import (
	"context"
	"fmt"
	"log/slog"
	"os"
	"strings"

	appengine "cloud.google.com/go/appengine/apiv1"
	"cloud.google.com/go/appengine/apiv1/appenginepb"
	"google.golang.org/protobuf/types/known/fieldmaskpb"
)

func main() {
	gaeRepo := InjectGAERepository()
	if gaeRepo == nil {
		slog.Error("Error creating App Engine client")
		return
	}
	defer gaeRepo.Close()

	// Application 情報の取得
	app, err := gaeRepo.GetDetails()
	if err != nil {
		slog.Error("Error getting App Engine details", "err", err)
		return
	}
	slog.Info("App Engine Application Info", "ID", app.Id, "Name", app.Name, "AuthDomain", app.AuthDomain)

	var newRules []*appenginepb.UrlDispatchRule
	switch strings.ToUpper(os.Getenv("MODE")) {
	case "ADD":
		for i, d := range app.DispatchRules {
			slog.Info(fmt.Sprintf("Existing Dispatch Rule %d", i), "Domain", d.Domain, "Path", d.Path, "Service", d.Service)
			if d.Domain == DispatchDomain &&
				d.Path == DispatchPathPattern &&
				d.Service == DispatchServiceName {
				slog.Info("Dispatch rule already exists. No changes made.")
				return
			}
		}
		// 新しいルールを追加(順番が優先順位になるため、先頭に追加)
		newRule := &appenginepb.UrlDispatchRule{
			Domain:  DispatchDomain,
			Path:    DispatchPathPattern,
			Service: DispatchServiceName,
		}
		newRules = append([]*appenginepb.UrlDispatchRule{newRule}, app.DispatchRules...)
	case "DELETE":
		// 既存の DispatchRules から該当ルールのみを除外
		isRuleRemoved := false
		for i, d := range app.DispatchRules {
			slog.Info(fmt.Sprintf("Existing Dispatch Rule %d", i), "Domain", d.Domain, "Path", d.Path, "Service", d.Service)
			if d.Domain == DispatchDomain &&
				d.Path == DispatchPathPattern &&
				d.Service == DispatchServiceName {
				isRuleRemoved = true
				continue // このルールを除外
			}
			newRules = append(newRules, d)
		}
		if !isRuleRemoved {
			slog.Info("No matching dispatch rule found to remove. No changes made.")
			return
		}
	default:
		slog.Error("Invalid MODE. Set MODE to 'ADD' or 'DELETE'.")
		return
	}

	req := gaeRepo.GenerateDispatchRulesUpdateRequest(newRules)
	_, err = gaeRepo.UpdateApplication(req)
	if err != nil {
		slog.Error("Error updating App Engine application", "err", err)
		return
	}
	slog.Info("Dispatch rules updated successfully.")
}

const (
	DispatchDomain      = "*"                   // 送信ルートのドメイン
	DispatchPathPattern = "/routing-target-url" // 送信ルートのパスパターン
	DispatchServiceName = "default"             // urlパターン(送信ルートのパスパターン)に一致したリクエストを処理するサービスの名前
)

type GAERepository struct {
	client *appengine.ApplicationsClient
}

func InjectGAERepository() *GAERepository {
	client, err := NewAppEngineClient()
	if err != nil {
		slog.Error("Error creating App Engine client", "err", err)
		return nil
	}
	return &GAERepository{client: client}
}

func NewAppEngineClient() (*appengine.ApplicationsClient, error) {
	ctx := context.Background()
	client, err := appengine.NewApplicationsClient(ctx)
	if err != nil {
		msg := fmt.Sprintf("Failed to create App Engine ApplicationsClient: %v", err)
		slog.Error(msg)
		return nil, err
	}
	slog.Info("App Engine ApplicationsClient initialized successfully.")
	return client, nil
}

func (r *GAERepository) Close() error {
	return r.client.Close()
}

// Application 情報の取得
func (r *GAERepository) GetDetails() (*appenginepb.Application, error) {
	ctx := context.Background()
	projectID := os.Getenv("PROJECT_ID")
	if projectID == "" {
		msg := "Environment variable PROJECT_ID is not set."
		slog.Error(msg)
		return nil, fmt.Errorf(msg)
	}
	// Application 名は "apps/{projectID}"
	req := &appenginepb.GetApplicationRequest{
		Name: "apps/" + projectID,
	}
	// Application 情報の取得
	app, err := r.client.GetApplication(ctx, req)
	if err != nil {
		msg := fmt.Sprintf("Failed to get application info for project %s: %v", projectID, err.Error())
		slog.Error(msg)
		return nil, err
	}
	slog.Info("Application details retrieved successfully.", "id", app.Id)

	return app, nil
}

// dispatch_rulesを更新するためのリクエストを生成
func (r *GAERepository) GenerateDispatchRulesUpdateRequest(newRules []*appenginepb.UrlDispatchRule) *appenginepb.UpdateApplicationRequest {
	projectID := os.Getenv("PROJECT_ID")
	req := &appenginepb.UpdateApplicationRequest{
		Name: "apps/" + projectID, // Application 名は "apps/{projectID}"
		Application: &appenginepb.Application{
			DispatchRules: newRules,
		},
		UpdateMask: &fieldmaskpb.FieldMask{
			Paths: []string{"dispatch_rules"}, // dispatchRules のみを更新する
			// フィールド名参照: https://cloud.google.com/appengine/docs/admin-api/reference/rest/v1/apps#Application
		},
	}
	return req
}

func (r *GAERepository) UpdateApplication(req *appenginepb.UpdateApplicationRequest) (*appenginepb.Application, error) {
	ctx := context.Background()
	op, err := r.client.UpdateApplication(ctx, req)
	if err != nil {
		msg := fmt.Sprintf("Failed to initiate application update: %v", err)
		slog.Error(msg)
		return nil, err
	}
	updatedApp, err := op.Wait(ctx)
	if err != nil {
		msg := fmt.Sprintf("Error waiting for application update to complete: %v", err)
		slog.Error(msg)
		return nil, err
	}
	slog.Info("Application updated successfully.", "id", updatedApp.Id)
	return updatedApp, nil
}

MODE=ADD にすると default サービスに /routing-target-url が追加され、
MODE=DELETE にすると そのルートが削除されます。