diff --git a/README.md b/README.md
index a563186..f6e67b2 100644
--- a/README.md
+++ b/README.md
@@ -278,6 +278,9 @@ exist yet, upaas has Docker create it as an empty directory, owned by root, when
the app's container starts; there is no need to create it first. An existing
host path is left as it is. This needs Docker Engine 23.0 or later.
+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.
+
## License
WTFPL
diff --git a/TODO.md b/TODO.md
index 6385244..9d51956 100644
--- a/TODO.md
+++ b/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's Volume mounts section says a deploy or rollback keeps
+ only the files the app wrote to its volume mounts (#248).
+
- 2026-10-01: Builds attach a BuildKit session, as the docker command line does,
so a base image that is not on the host is pulled instead of the build failing
with "no active sessions" on Docker Engine 27. Container logs, and so the
diff --git a/internal/handlers/app.go b/internal/handlers/app.go
index e03faf8..7258327 100644
--- a/internal/handlers/app.go
+++ b/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,
diff --git a/internal/handlers/app_no_volumes_test.go b/internal/handlers/app_no_volumes_test.go
new file mode 100644
index 0000000..65b96bd
--- /dev/null
+++ b/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)
+}
diff --git a/internal/service/deploy/deploy.go b/internal/service/deploy/deploy.go
index 4245be2..9af52d0 100644
--- a/internal/service/deploy/deploy.go
+++ b/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
diff --git a/internal/service/deploy/deploy_volumes_test.go b/internal/service/deploy/deploy_volumes_test.go
new file mode 100644
index 0000000..35aed12
--- /dev/null
+++ b/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)
+}
diff --git a/templates/app_detail.html b/templates/app_detail.html
index eb6f146..7166a69 100644
--- a/templates/app_detail.html
+++ b/templates/app_detail.html
@@ -318,6 +318,8 @@
+ {{else}}
+ {{.NoVolumesWarning}}
{{end}}