Say that a deploy keeps only an app's volumes when the app has none (closes #248)

An app with no volume mounts now shows, in its Volume Mounts section,
that the files it writes are lost whenever a deploy or rollback replaces
its container and that a restart keeps them. Each deploy of such an app
writes the same sentence into its log, after the webhook payload and
before the clone. The README says in one sentence that a deploy or
rollback starts a new container that keeps only the files in the app's
volume mounts.

Model: opus-5-5

README.md

@@ -16,6 +16,9 @@ repositories via webhooks from Gitea, GitHub, or GitLab.
 - Notifications via ntfy and Slack-compatible webhooks
 - Simple server-rendered UI with Tailwind CSS
 
+A deploy or rollback replaces the app's container with a new one, which keeps
+only the files the app wrote to its volume mounts.
+
 ## Non-Goals
 
 - Multi-user support

TODO.md

@@ -20,6 +20,11 @@ regress.
 
 # Completed Steps
 
+- 2026-10-01: An app with no volume mounts says on its page, and in the log of
+  each deploy, that a deploy or rollback loses the files it writes and a restart
+  keeps them; the README says a deploy or rollback keeps only the files the app
+  wrote to its volume mounts (#248).
+
 - 2026-09-29: The app page is 50% wider on large screens (84rem instead of
   56rem), its build log and container log boxes are twice as tall, the build log
   sits between the webhook URL and the environment variables, and the container

internal/handlers/app.go

@@ -21,6 +21,7 @@ import (
 	"sneak.berlin/go/upaas/internal/database"
 	"sneak.berlin/go/upaas/internal/models"
 	"sneak.berlin/go/upaas/internal/service/app"
+	"sneak.berlin/go/upaas/internal/service/deploy"
 	"sneak.berlin/go/upaas/templates"
 )
 
@@ -194,6 +195,7 @@ func (h *Handlers) HandleAppDetail() http.HandlerFunc {
 			"EnvVars":          envVars,
 			"Labels":           labels,
 			"Volumes":          volumes,
+			"NoVolumesWarning": deploy.NoVolumesWarning,
 			"Ports":            ports,
 			"Deployments":      deployments,
 			"LatestDeployment": latestDeployment,

internal/handlers/app_no_volumes_test.go

@@ -0,0 +1,45 @@
+package handlers_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"sneak.berlin/go/upaas/internal/models"
+	"sneak.berlin/go/upaas/internal/service/deploy"
+)
+
+// TestAppPageSaysFilesAreLostOnlyWhenAppHasNoVolumes checks that the app page
+// shows deploy.NoVolumesWarning until the app gets a volume mount.
+func TestAppPageSaysFilesAreLostOnlyWhenAppHasNoVolumes(t *testing.T) {
+	t.Parallel()
+
+	testCtx := setupTestHandlers(t)
+	createdApp := createTestApp(t, testCtx, "no-volumes-app")
+
+	renderAppPage := func() string {
+		request := httptest.NewRequestWithContext(
+			t.Context(), http.MethodGet, "/apps/"+createdApp.ID, nil,
+		)
+		request = addChiURLParams(request, map[string]string{"id": createdApp.ID})
+		recorder := httptest.NewRecorder()
+
+		testCtx.handlers.HandleAppDetail().ServeHTTP(recorder, request)
+		require.Equal(t, http.StatusOK, recorder.Code)
+
+		return recorder.Body.String()
+	}
+
+	assert.Contains(t, renderAppPage(), deploy.NoVolumesWarning)
+
+	volume := models.NewVolume(testCtx.database)
+	volume.AppID = createdApp.ID
+	volume.HostPath = "/srv/no-volumes-app"
+	volume.ContainerPath = "/data"
+	require.NoError(t, volume.Save(t.Context()))
+
+	assert.NotContains(t, renderAppPage(), deploy.NoVolumesWarning)
+}

internal/service/deploy/deploy.go

@@ -56,6 +56,12 @@ var (
 	ErrNoPreviousImage = errors.New("no previous image available for rollback")
 )
 
+// NoVolumesWarning is shown on the page of an app with no volume mounts and
+// written into each of its deploy logs.
+const NoVolumesWarning = "This app has no volume mounts, so the files it writes " +
+	"are lost whenever a deploy or rollback replaces its container; " +
+	"a restart of the container keeps them."
+
 // logFlushInterval is how often to flush buffered logs to the database.
 const logFlushInterval = time.Second
 
@@ -369,6 +375,11 @@ func (svc *Service) Deploy(
 
 	svc.logWebhookPayload(bgCtx, deployment, webhookEvent)
 
+	volumes, err := app.GetVolumes(bgCtx)
+	if err == nil && len(volumes) == 0 {
+		_ = deployment.AppendLog(bgCtx, NoVolumesWarning)
+	}
+
 	err = svc.updateAppStatusBuilding(bgCtx, app)
 	if err != nil {
 		return err

internal/service/deploy/deploy_volumes_test.go

@@ -0,0 +1,79 @@
+package deploy_test
+
+import (
+	"context"
+	"log/slog"
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"sneak.berlin/go/upaas/internal/config"
+	"sneak.berlin/go/upaas/internal/database"
+	"sneak.berlin/go/upaas/internal/docker"
+	"sneak.berlin/go/upaas/internal/logger"
+	"sneak.berlin/go/upaas/internal/models"
+	"sneak.berlin/go/upaas/internal/service/deploy"
+	"sneak.berlin/go/upaas/internal/service/notify"
+)
+
+// deployLog deploys a new app, with one volume mount when withVolume is set,
+// and returns the deploy's log. Docker is not connected, so the deploy fails
+// at the git clone, after the start of its log is written.
+func deployLog(t *testing.T, withVolume bool) string {
+	t.Helper()
+
+	log := logger.NewForTest(slog.New(slog.NewTextHandler(os.Stderr, nil)))
+	dataDir := t.TempDir()
+	cfg := &config.Config{DataDir: dataDir, HostDataDir: dataDir}
+	db := database.NewTestDatabase(t)
+
+	dockerClient, err := docker.New(nil, docker.Params{Logger: log, Config: cfg})
+	require.NoError(t, err)
+
+	notifySvc, err := notify.New(nil, notify.ServiceParams{Logger: log})
+	require.NoError(t, err)
+
+	svc, err := deploy.New(nil, deploy.ServiceParams{
+		Logger: log, Config: cfg, Database: db,
+		Docker: dockerClient, Notify: notifySvc,
+	})
+	require.NoError(t, err)
+
+	ctx := context.Background()
+
+	app := models.NewApp(db)
+	app.ID = "volumesapp-id"
+	app.Name = "volumesapp"
+	app.Branch = "main"
+	require.NoError(t, app.Save(ctx))
+
+	if withVolume {
+		volume := models.NewVolume(db)
+		volume.AppID = app.ID
+		volume.HostPath = "/srv/volumesapp"
+		volume.ContainerPath = "/data"
+		require.NoError(t, volume.Save(ctx))
+	}
+
+	err = svc.Deploy(ctx, app, nil, false)
+	require.ErrorIs(t, err, docker.ErrNotConnected)
+
+	deployments, err := app.GetDeployments(ctx, 1)
+	require.NoError(t, err)
+	require.Len(t, deployments, 1)
+
+	return deployments[0].Logs.String
+}
+
+func TestDeployLogSaysFilesAreLostOnlyWhenAppHasNoVolumes(t *testing.T) {
+	t.Parallel()
+
+	logWithoutVolumes := deployLog(t, false)
+	assert.Equal(t, 1, strings.Count(logWithoutVolumes, deploy.NoVolumesWarning),
+		logWithoutVolumes)
+
+	assert.NotContains(t, deployLog(t, true), deploy.NoVolumesWarning)
+}

templates/app_detail.html

@@ -318,6 +318,8 @@
                 </tbody>
             </table>
         </div>
+        {{else}}
+        <p class="alert-warning">{{.NoVolumesWarning}}</p>
         {{end}}
         <form method="POST" action="/apps/{{.App.ID}}/volumes" class="flex flex-col sm:flex-row gap-2 items-end">
                 {{ .CSRFField }}