[feature] Use maintenance router to serve 503 while server is starting/migrating (#3705)

* [feature] Use maintenance router to serve 503 while server is starting/migrating

* love you linter, kissies

cmd/gotosocial/action/server/server.go

@@ -69,6 +69,36 @@
 	"go.uber.org/automaxprocs/maxprocs"
 )
 
+// Maintenance starts and creates a GoToSocial server
+// in maintenance mode (returns 503 for most requests).
+var Maintenance action.GTSAction = func(ctx context.Context) error {
+	route, err := router.New(ctx)
+	if err != nil {
+		return fmt.Errorf("error creating maintenance router: %w", err)
+	}
+
+	// Route maintenance handlers.
+	maintenance := web.NewMaintenance()
+	maintenance.Route(route)
+
+	// Start the maintenance router.
+	if err := route.Start(); err != nil {
+		return fmt.Errorf("error starting maintenance router: %w", err)
+	}
+
+	// Catch shutdown signals from the OS.
+	sigs := make(chan os.Signal, 1)
+	signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)
+	sig := <-sigs // block until signal received
+	log.Infof(ctx, "received signal %s, shutting down", sig)
+
+	if err := route.Stop(); err != nil {
+		log.Errorf(ctx, "error stopping router: %v", err)
+	}
+
+	return nil
+}
+
 // Start creates and starts a gotosocial server
 var Start action.GTSAction = func(ctx context.Context) error {
 	// Set GOMAXPROCS / GOMEMLIMIT
@@ -148,6 +178,23 @@
 		log.Info(ctx, "done! exiting...")
 	}()
 
+	// Create maintenance router.
+	var err error
+	route, err = router.New(ctx)
+	if err != nil {
+		return fmt.Errorf("error creating maintenance router: %w", err)
+	}
+
+	// Route maintenance handlers.
+	maintenance := web.NewMaintenance()
+	maintenance.Route(route)
+
+	// Start the maintenance router to handle reqs
+	// while the instance is starting up / migrating.
+	if err := route.Start(); err != nil {
+		return fmt.Errorf("error starting maintenance router: %w", err)
+	}
+
 	// Initialize tracing (noop if not enabled).
 	if err := tracing.Initialize(); err != nil {
 		return fmt.Errorf("error initializing tracing: %w", err)
@@ -359,9 +406,15 @@ func(context.Context, time.Time) {
 		HTTP router initialization
 	*/
 
+	// Close down the maintenance router.
+	if err := route.Stop(); err != nil {
+		return fmt.Errorf("error stopping maintenance router: %w", err)
+	}
+
+	// Instantiate the main router.
 	route, err = router.New(ctx)
 	if err != nil {
-		return fmt.Errorf("error creating router: %s", err)
+		return fmt.Errorf("error creating main router: %s", err)
 	}
 
 	// Start preparing middleware stack.

cmd/gotosocial/server.go

@@ -41,5 +41,19 @@ func serverCommands() *cobra.Command {
 	}
 	config.AddServerFlags(serverStartCmd)
 	serverCmd.AddCommand(serverStartCmd)
+
+	serverMaintenanceCmd := &cobra.Command{
+		Use:   "maintenance",
+		Short: "start the gotosocial server in maintenance mode (returns 503 for almost all requests)",
+		PreRunE: func(cmd *cobra.Command, args []string) error {
+			return preRun(preRunArgs{cmd: cmd})
+		},
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return run(cmd.Context(), server.Maintenance)
+		},
+	}
+	config.AddServerFlags(serverMaintenanceCmd)
+	serverCmd.AddCommand(serverMaintenanceCmd)
+
 	return serverCmd
 }

internal/web/assets.go

@@ -21,10 +21,13 @@
 	"fmt"
 	"net/http"
 	"path"
+	"path/filepath"
 	"strings"
 
 	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
 	"github.com/superseriousbusiness/gotosocial/internal/log"
+	"github.com/superseriousbusiness/gotosocial/internal/router"
 )
 
 type fileSystem struct {
@@ -53,7 +56,11 @@ func (fs fileSystem) Open(path string) (http.File, error) {
 // getAssetFileInfo tries to fetch the ETag for the given filePath from the module's
 // assetsETagCache. If it can't be found there, it uses the provided http.FileSystem
 // to generate a new ETag to go in the cache, which it then returns.
-func (m *Module) getAssetETag(filePath string, fs http.FileSystem) (string, error) {
+func getAssetETag(
+	wet withETagCache,
+	filePath string,
+	fs http.FileSystem,
+) (string, error) {
 	file, err := fs.Open(filePath)
 	if err != nil {
 		return "", fmt.Errorf("error opening %s: %s", filePath, err)
@@ -67,7 +74,8 @@ func (m *Module) getAssetETag(filePath string, fs http.FileSystem) (string, erro
 
 	fileLastModified := fileInfo.ModTime()
 
-	if cachedETag, ok := m.eTagCache.Get(filePath); ok && !fileLastModified.After(cachedETag.lastModified) {
+	cache := wet.ETagCache()
+	if cachedETag, ok := cache.Get(filePath); ok && !fileLastModified.After(cachedETag.lastModified) {
 		// only return our cached etag if the file wasn't
 		// modified since last time, otherwise generate a
 		// new one; eat fresh!
@@ -80,7 +88,7 @@ func (m *Module) getAssetETag(filePath string, fs http.FileSystem) (string, erro
 	}
 
 	// put new entry in cache before we return
-	m.eTagCache.Set(filePath, eTagCacheEntry{
+	cache.Set(filePath, eTagCacheEntry{
 		eTag:         eTag,
 		lastModified: fileLastModified,
 	})
@@ -99,7 +107,10 @@ func (m *Module) getAssetETag(filePath string, fs http.FileSystem) (string, erro
 //
 // todo: move this middleware out of the 'web' package and into the 'middleware'
 // package along with the other middlewares
-func (m *Module) assetsCacheControlMiddleware(fs http.FileSystem) gin.HandlerFunc {
+func assetsCacheControlMiddleware(
+	wet withETagCache,
+	fs http.FileSystem,
+) gin.HandlerFunc {
 	return func(c *gin.Context) {
 		// Acquire context from gin request.
 		ctx := c.Request.Context()
@@ -118,7 +129,7 @@ func (m *Module) assetsCacheControlMiddleware(fs http.FileSystem) gin.HandlerFun
 		assetFilePath := strings.TrimPrefix(path.Clean(upath), assetsPathPrefix)
 
 		// either fetch etag from ttlcache or generate it
-		eTag, err := m.getAssetETag(assetFilePath, fs)
+		eTag, err := getAssetETag(wet, assetFilePath, fs)
 		if err != nil {
 			log.Errorf(ctx, "error getting ETag for %s: %s", assetFilePath, err)
 			return
@@ -137,3 +148,23 @@ func (m *Module) assetsCacheControlMiddleware(fs http.FileSystem) gin.HandlerFun
 		// else let the rest of the request be processed normally
 	}
 }
+
+// routeAssets attaches *just* the
+// assets filesystem to the given router.
+func routeAssets(
+	wet withETagCache,
+	r *router.Router,
+	mi ...gin.HandlerFunc,
+) {
+	// Group all static files from assets dir at /assets,
+	// so that they can use the same cache control middleware.
+	webAssetsAbsFilePath, err := filepath.Abs(config.GetWebAssetBaseDir())
+	if err != nil {
+		log.Panicf(nil, "error getting absolute path of assets dir: %s", err)
+	}
+	fs := fileSystem{http.Dir(webAssetsAbsFilePath)}
+	assetsGroup := r.AttachGroup(assetsPathPrefix)
+	assetsGroup.Use(assetsCacheControlMiddleware(wet, fs))
+	assetsGroup.Use(mi...)
+	assetsGroup.StaticFS("/", fs)
+}

internal/web/etag.go

@@ -29,6 +29,10 @@
 	"codeberg.org/gruf/go-cache/v3"
 )
 
+type withETagCache interface {
+	ETagCache() cache.Cache[string, eTagCacheEntry]
+}
+
 func newETagCache() cache.TTLCache[string, eTagCacheEntry] {
 	eTagCache := cache.NewTTL[string, eTagCacheEntry](0, 1000, 0)
 	eTagCache.SetTTL(time.Hour, false)

internal/web/maintenance.go

@@ -0,0 +1,70 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package web
+
+import (
+	"net/http"
+	"time"
+
+	"codeberg.org/gruf/go-cache/v3"
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/api/health"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/router"
+)
+
+type MaintenanceModule struct {
+	eTagCache cache.Cache[string, eTagCacheEntry]
+}
+
+// NewMaintenance returns a module that routes only
+// static assets, and returns a code 503 maintenance
+// message template to all other requests.
+func NewMaintenance() *MaintenanceModule {
+	return &MaintenanceModule{
+		eTagCache: newETagCache(),
+	}
+}
+
+// ETagCache implements withETagCache.
+func (m *MaintenanceModule) ETagCache() cache.Cache[string, eTagCacheEntry] {
+	return m.eTagCache
+}
+
+func (m *MaintenanceModule) Route(r *router.Router, mi ...gin.HandlerFunc) {
+	// Route static assets.
+	routeAssets(m, r, mi...)
+
+	// Serve OK in response to live
+	// requests, but not ready requests.
+	liveHandler := func(c *gin.Context) {
+		c.Status(http.StatusOK)
+	}
+	r.AttachHandler(http.MethodGet, health.LivePath, liveHandler)
+	r.AttachHandler(http.MethodHead, health.LivePath, liveHandler)
+
+	// For everything else, serve maintenance template.
+	obj := map[string]string{"host": config.GetHost()}
+	r.AttachNoRouteHandler(func(c *gin.Context) {
+		retryAfter := time.Now().Add(120 * time.Second).UTC()
+		c.Writer.Header().Add("Retry-After", "120")
+		c.Writer.Header().Add("Retry-After", retryAfter.Format(http.TimeFormat))
+		c.Header("Cache-Control", "no-store")
+		c.HTML(http.StatusServiceUnavailable, "maintenance.tmpl", obj)
+	})
+}

internal/web/web.go

@@ -21,14 +21,11 @@
 	"context"
 	"net/http"
 	"net/url"
-	"path/filepath"
 
 	"codeberg.org/gruf/go-cache/v3"
 	"github.com/gin-gonic/gin"
 	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
-	"github.com/superseriousbusiness/gotosocial/internal/config"
 	"github.com/superseriousbusiness/gotosocial/internal/db"
-	"github.com/superseriousbusiness/gotosocial/internal/log"
 	"github.com/superseriousbusiness/gotosocial/internal/middleware"
 	"github.com/superseriousbusiness/gotosocial/internal/processing"
 	"github.com/superseriousbusiness/gotosocial/internal/router"
@@ -87,22 +84,22 @@ func New(db db.DB, processor *processing.Processor) *Module {
 	}
 }
 
-func (m *Module) Route(r *router.Router, mi ...gin.HandlerFunc) {
-	// Group all static files from assets dir at /assets,
-	// so that they can use the same cache control middleware.
-	webAssetsAbsFilePath, err := filepath.Abs(config.GetWebAssetBaseDir())
-	if err != nil {
-		log.Panicf(nil, "error getting absolute path of assets dir: %s", err)
+// ETagCache implements withETagCache.
+func (m *Module) ETagCache() cache.Cache[string, eTagCacheEntry] {
+	return m.eTagCache
 }
-	fs := fileSystem{http.Dir(webAssetsAbsFilePath)}
-	assetsGroup := r.AttachGroup(assetsPathPrefix)
-	assetsGroup.Use(m.assetsCacheControlMiddleware(fs))
-	assetsGroup.Use(mi...)
-	assetsGroup.StaticFS("/", fs)
 
-	// handlers that serve profiles and statuses should use the SignatureCheck
-	// middleware, so that requests with content-type application/activity+json
-	// can still be served
+// Route attaches the assets filesystem and profile,
+// status, and other web handlers to the router.
+func (m *Module) Route(r *router.Router, mi ...gin.HandlerFunc) {
+	// Route static assets.
+	routeAssets(m, r, mi...)
+
+	// Route all other endpoints + handlers.
+	//
+	// Handlers that serve profiles and statuses should use
+	// the SignatureCheck middleware, so that requests with
+	// content-type application/activity+json can be served
 	profileGroup := r.AttachGroup(profileGroupPath)
 	profileGroup.Use(mi...)
 	profileGroup.Use(middleware.SignatureCheck(m.isURIBlocked), middleware.CacheControl(middleware.CacheControlConfig{
@@ -111,7 +108,7 @@ func (m *Module) Route(r *router.Router, mi ...gin.HandlerFunc) {
 	profileGroup.Handle(http.MethodGet, "", m.profileGETHandler) // use empty path here since it's the base of the group
 	profileGroup.Handle(http.MethodGet, statusPath, m.threadGETHandler)
 
-	// Attach individual web handlers which require no specific middlewares
+	// Individual web handlers requiring no specific middlewares.
 	r.AttachHandler(http.MethodGet, "/", m.indexHandler) // front-page
 	r.AttachHandler(http.MethodGet, settingsPathPrefix, m.SettingsPanelHandler)
 	r.AttachHandler(http.MethodGet, settingsPanelGlob, m.SettingsPanelHandler)
@@ -128,7 +125,7 @@ func (m *Module) Route(r *router.Router, mi ...gin.HandlerFunc) {
 	r.AttachHandler(http.MethodGet, signupPath, m.signupGETHandler)
 	r.AttachHandler(http.MethodPost, signupPath, m.signupPOSTHandler)
 
-	// Attach redirects from old endpoints to current ones for backwards compatibility
+	// Redirects from old endpoints to for back compat.
 	r.AttachHandler(http.MethodGet, "/auth/edit", func(c *gin.Context) { c.Redirect(http.StatusMovedPermanently, userPanelPath) })
 	r.AttachHandler(http.MethodGet, "/user", func(c *gin.Context) { c.Redirect(http.StatusMovedPermanently, userPanelPath) })
 	r.AttachHandler(http.MethodGet, "/admin", func(c *gin.Context) { c.Redirect(http.StatusMovedPermanently, adminPanelPath) })

web/template/maintenance.tmpl

@@ -0,0 +1,76 @@
+{{- /*
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/ -}}
+
+<!DOCTYPE html>
+<html lang="en">
+    <head>
+        <meta charset="UTF-8">
+        <meta http-equiv="X-UA-Compatible" content="IE=edge">
+        <meta name="viewport" content="width=device-width, initial-scale=1.0">
+        <meta name="robots" content="noindex, nofollow">
+        <link rel="icon" href="/assets/logo.webp" type="image/webp">
+        <link rel="apple-touch-icon" href="/assets/logo.webp" type="image/webp">
+        <link rel="apple-touch-startup-image" href="/assets/logo.webp" type="image/webp">
+        <link rel="preload" href="/assets/dist/_colors.css" as="style">
+        <link rel="preload" href="/assets/dist/base.css" as="style">
+        <link rel="preload" href="/assets/dist/page.css" as="style">
+        <link rel="stylesheet" href="/assets/dist/_colors.css">
+        <link rel="stylesheet" href="/assets/dist/base.css">
+        <link rel="stylesheet" href="/assets/dist/page.css">
+        <title>{{- .host -}}</title>
+    </head>
+    <body>
+        <div class="page">
+        <header class="page-header">
+            <a aria-label="{{- .host -}}. Go to instance homepage" href="/" class="nounderline">
+                <picture>
+                    <img
+                        src="/assets/logo.webp"
+                        alt="A cartoon sloth smiling happily."
+                        title="A cartoon sloth smiling happily."
+                    />
+                </picture>
+                <h1>{{- .host -}}</h1>
+            </a>
+        </header>
+        <div class="page-content">
+            <p>This GoToSocial instance is currently down for maintenance, starting up, or running database migrations. Please wait.</p>
+            <p>If you are the admin of this instance, check your GoToSocial logs for more details, and make sure to <strong>not interrupt any running database migrations</strong>!</p>
+        </div>
+        <footer class="page-footer">
+            <nav>
+                <ul class="nodot">
+                    <li id="version">
+                        <a
+                            href="https://github.com/superseriousbusiness/gotosocial"
+                            class="nounderline"
+                            rel="nofollow noreferrer noopener"
+                            target="_blank"
+                        >
+                            <span aria-hidden="true">🦥</span>
+                            Source - GoToSocial
+                            <span aria-hidden="true">🦥</span>
+                        </a>
+                    </li>
+                </ul>
+            </nav>
+        </footer>
+        </div>
+    </body>
+</html>