List every setting upaas reads in the README Configuration table (closes #229)

The table left out UPAAS_MAINTENANCE_MODE, UPAAS_SESSION_SECRET and
UPAAS_CORS_ORIGINS, and several rows gave the wrong default or effect.
Each row now matches internal/config/config.go and the code that uses
the value: UPAAS_PORT is also read and wins over PORT, UPAAS_DATA_DIR
must be absolute for deploys unless UPAAS_HOST_DATA_DIR is set,
UPAAS_HOST_DATA_DIR falls back to UPAAS_DATA_DIR and must be absolute
when set, UPAAS_DEBUG also drops the session cookie's Secure flag,
UPAAS_SENTRY_DSN is not used, and /metrics exists only when
UPAAS_METRICS_USERNAME is set. A sentence under the table names the
standard Docker client variables. TODO.md records the step.

Model: opus-5-5

.dockerignore

@@ -1,4 +1,5 @@
 .git
+.env
 bin/
 .editorconfig
 .vscode/

README.md

@@ -192,16 +192,23 @@ This ensures the main branch always contains clean, tested, working code.
 Environment variables:
 
 | Variable                 | Description                                                                                                                                                                                              | Default                                           |
-| ---------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------- |
-| `PORT`                 | HTTP listen port                                                                                                                                                       | 8080                                                     |
-| `UPAAS_DATA_DIR`       | Data directory for SQLite and keys                                                                                                                                     | `./data` (local dev only — use absolute path for Docker) |
-| `UPAAS_HOST_DATA_DIR`  | Host path for DATA_DIR (when running in container)                                                                                                                     | _(none — must be set to an absolute path)_               |
-| `UPAAS_DOCKER_HOST`    | Docker socket path                                                                                                                                                     | unix:///var/run/docker.sock                              |
+| ------------------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------- |
+| `PORT`                   | HTTP listen port. `UPAAS_PORT` is also read and wins when both are set.                                                                                                                                  | 8080                                              |
+| `UPAAS_DATA_DIR`         | Directory for the SQLite database, session key, builds and deployment logs. Deploys need it to be an absolute path unless `UPAAS_HOST_DATA_DIR` is set.                                                  | `./data` (the Docker image sets `/var/lib/upaas`) |
+| `UPAAS_HOST_DATA_DIR`    | Host path of `UPAAS_DATA_DIR`, needed when upaas runs in a container so the bind mounts it passes to Docker point at the right host directory. When set, it must be absolute, or upaas refuses to start. | the value of `UPAAS_DATA_DIR`                     |
+| `UPAAS_DOCKER_HOST`      | Docker daemon address                                                                                                                                                                                    | unix:///var/run/docker.sock                       |
 | `UPAAS_PLAINTEXT_HTTP`   | Set when µPaaS is reached over plain HTTP (no TLS-terminating proxy in front) so CSRF origin checks use `http://`. Leave unset behind a TLS-terminating reverse proxy.                                   | false                                             |
-| `DEBUG`                | Enable debug logging                                                                                                                                                   | false                                                    |
-| `SENTRY_DSN`           | Sentry error reporting DSN                                                                                                                                             | ""                                                       |
-| `METRICS_USERNAME`     | Basic auth for /metrics                                                                                                                                                | ""                                                       |
-| `METRICS_PASSWORD`     | Basic auth for /metrics                                                                                                                                                | ""                                                       |
+| `UPAAS_DEBUG`            | Enable debug logging. Also sends the session cookie without the `Secure` flag.                                                                                                                           | false                                             |
+| `UPAAS_SENTRY_DSN`       | Read but not used: upaas sends nothing to Sentry                                                                                                                                                         | ""                                                |
+| `UPAAS_METRICS_USERNAME` | When set, `/metrics` is served behind basic auth with this username. When unset, there is no `/metrics`.                                                                                                 | ""                                                |
+| `UPAAS_METRICS_PASSWORD` | Basic auth password for `/metrics`                                                                                                                                                                       | ""                                                |
+| `UPAAS_MAINTENANCE_MODE` | Only shown as `maintenanceMode` in the `/health` response; it blocks nothing                                                                                                                             | false                                             |
+| `UPAAS_SESSION_SECRET`   | Key that signs the session and CSRF cookies. When unset, a random key is generated once and kept in `$UPAAS_DATA_DIR/session.key`.                                                                       | ""                                                |
+| `UPAAS_CORS_ORIGINS`     | Comma-separated origins allowed to make cross-origin requests with cookies. When unset, no CORS headers are sent.                                                                                        | ""                                                |
+
+The Docker client also reads the standard `DOCKER_API_VERSION`,
+`DOCKER_CERT_PATH` and `DOCKER_TLS_VERIFY` variables; `UPAAS_DOCKER_HOST`, which
+has a default, always overrides `DOCKER_HOST`.
 
 ## Running with Docker
 
@@ -219,39 +226,30 @@ This recipe serves plain HTTP, so `UPAAS_PLAINTEXT_HTTP=true` is required for
 setup and every other form to pass the CSRF origin check. Behind a
 TLS-terminating reverse proxy, drop that line.
 
-### Docker Compose
+### Deploying with Docker Compose
 
-```yaml
-services:
-    upaas:
-        build: .
-        restart: unless-stopped
-        ports:
-            - "8080:8080"
-        volumes:
-            - /var/run/docker.sock:/var/run/docker.sock
-            - ${HOST_DATA_DIR}:/var/lib/upaas
-        environment:
-            - UPAAS_HOST_DATA_DIR=${HOST_DATA_DIR}
-            # Set when serving plain HTTP (no TLS-terminating proxy); drop behind one
-            - UPAAS_PLAINTEXT_HTTP=true
-            # Optional: uncomment to enable debug logging
-            # - DEBUG=true
-            # Optional: Sentry error reporting
-            # - SENTRY_DSN=https://...
-            # Optional: Prometheus metrics auth
-            # - METRICS_USERNAME=prometheus
-            # - METRICS_PASSWORD=secret
+[`docker-compose.yml`](docker-compose.yml) builds the image from this repo and
+runs it with the Docker socket and the data directory mounted. It reads its
+settings from a `.env` file next to it, which needs at least:
+
+```bash
+HOST_DATA_DIR=/srv/upaas/data
 ```
 
-**Important**: You **must** set `HOST_DATA_DIR` to an **absolute path** on the
-host before running `docker compose up`. This value is bind-mounted into the
-container and passed as `UPAAS_HOST_DATA_DIR` so that Docker bind mounts during
-builds resolve correctly. Relative paths (e.g. `./data`) will break container
-builds because the Docker daemon resolves paths relative to the host, not the
-container.
+Other settings from [Configuration](#configuration) go in the same file, except
+`PORT` and `UPAAS_DATA_DIR`: the compose file sets them to 8080 and
+`/var/lib/upaas`, overriding `.env`, to match its port mapping, healthcheck and
+data directory mount. Then run `docker compose up -d` from the repo root;
+`docker compose ps` shows the container as healthy once `/health` answers.
 
-Example: `HOST_DATA_DIR=/srv/upaas/data docker compose up -d`
+**Important**: `HOST_DATA_DIR` **must** be an **absolute path** on the host. It
+is bind-mounted into the container and passed as `UPAAS_HOST_DATA_DIR` so that
+Docker bind mounts during builds resolve correctly, because the Docker daemon
+resolves paths on the host, not in the container. upaas refuses to start when
+`UPAAS_HOST_DATA_DIR` is a relative path such as `./data`.
+
+The port is published on `127.0.0.1:8080` only, for a TLS-terminating reverse
+proxy in front of it. Leave `UPAAS_PLAINTEXT_HTTP` unset behind that proxy.
 
 Apps are built with BuildKit, so the stages of a multi-stage build are kept in
 Docker's build cache rather than as untagged images. Docker Engine 28.2 and

TODO.md

@@ -20,6 +20,24 @@ regress.
 
 # Completed Steps
 
+- 2026-09-29: The README Configuration table now lists every setting upaas
+  reads, adding `UPAAS_MAINTENANCE_MODE`, `UPAAS_SESSION_SECRET` and
+  `UPAAS_CORS_ORIGINS`, and gives the real default and effect of each:
+  `UPAAS_PORT` wins over `PORT`, `UPAAS_HOST_DATA_DIR` falls back to
+  `UPAAS_DATA_DIR`, `UPAAS_DEBUG` drops the session cookie's `Secure` flag, and
+  `UPAAS_SENTRY_DSN` is not used (#229).
+
+- 2026-09-28: The README Configuration table now names `UPAAS_DEBUG`,
+  `UPAAS_SENTRY_DSN`, `UPAAS_METRICS_USERNAME` and `UPAAS_METRICS_PASSWORD`, the
+  names upaas actually reads (the unprefixed names it listed were ignored), and
+  the `UPAAS_HOST_DATA_DIR` row refers to `UPAAS_DATA_DIR` (#224).
+
+- 2026-09-28: Added `docker-compose.yml` for deploying upaas: settings from
+  `.env`, the port published on `127.0.0.1` only for a TLS proxy in front, and a
+  healthcheck against `/health`; the README's plain-HTTP Compose example is
+  replaced by a short deploy section. upaas now refuses to start when
+  `UPAAS_HOST_DATA_DIR` is set to a relative path (#223).
+
 - 2026-09-23: Apps are now built with BuildKit, so the stages of a multi-stage
   build stay in Docker's size-limited build cache instead of piling up as
   untagged images; build progress is still written to the deployment log as

docker-compose.yml

@@ -0,0 +1,30 @@
+# Runs upaas. Put settings in .env next to this file; see "Deploying with
+# Docker Compose" in README.md.
+services:
+  upaas:
+    build: .
+    restart: unless-stopped
+    # Every line of .env is passed to upaas as an environment variable.
+    env_file: .env
+    environment:
+      # Overrides any PORT in .env, so upaas listens where the port mapping
+      # and healthcheck below expect it.
+      PORT: "8080"
+      # Overrides any UPAAS_DATA_DIR in .env, so the database stays on the
+      # HOST_DATA_DIR mount below instead of inside the container.
+      UPAAS_DATA_DIR: /var/lib/upaas
+      # The Docker daemon resolves app bind mounts on the host, so upaas must
+      # know the host path of its data directory.
+      UPAAS_HOST_DATA_DIR: ${HOST_DATA_DIR:?set HOST_DATA_DIR in .env to an absolute host path}
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+      - ${HOST_DATA_DIR:?set HOST_DATA_DIR in .env to an absolute host path}:/var/lib/upaas
+    # Loopback only, for a TLS-terminating reverse proxy in front. Leave
+    # UPAAS_PLAINTEXT_HTTP unset behind that proxy.
+    ports:
+      - "127.0.0.1:8080:8080"
+    healthcheck:
+      test: ["CMD", "wget", "-q", "-O", "/dev/null", "http://127.0.0.1:8080/health"]
+      interval: 30s
+      timeout: 5s
+      retries: 3

internal/config/config.go

@@ -32,6 +32,12 @@ const (
 	filePermissions = 0o600
 )
 
+// errHostDataDirNotAbsolute is returned when UPAAS_HOST_DATA_DIR is set to a
+// relative path, which the Docker daemon cannot resolve for app bind mounts.
+var errHostDataDirNotAbsolute = errors.New(
+	"UPAAS_HOST_DATA_DIR must be an absolute path",
+)
+
 // Params contains dependencies for Config.
 type Params struct {
 	fx.In
@@ -124,6 +130,10 @@ func buildConfig(log *slog.Logger, params *Params) (*Config, error) {
 	dataDir := viper.GetString("DATA_DIR")
 	hostDataDir := viper.GetString("HOST_DATA_DIR")
 
+	if hostDataDir != "" && !filepath.IsAbs(hostDataDir) {
+		return nil, fmt.Errorf("%w, got %q", errHostDataDirNotAbsolute, hostDataDir)
+	}
+
 	if hostDataDir == "" {
 		hostDataDir = dataDir
 	}

internal/config/config_test.go

@@ -0,0 +1,33 @@
+package config //nolint:testpackage // tests unexported buildConfig
+
+import (
+	"errors"
+	"log/slog"
+	"testing"
+)
+
+func TestBuildConfigRejectsRelativeHostDataDir(t *testing.T) {
+	t.Setenv("UPAAS_HOST_DATA_DIR", "./data")
+	setupViper("upaas")
+
+	_, err := buildConfig(slog.Default(), &Params{})
+	if !errors.Is(err, errHostDataDirNotAbsolute) {
+		t.Fatalf("expected errHostDataDirNotAbsolute, got %v", err)
+	}
+}
+
+func TestBuildConfigHostDataDirDefaultsToDataDir(t *testing.T) {
+	t.Setenv("UPAAS_DATA_DIR", "./data")
+	t.Setenv("UPAAS_HOST_DATA_DIR", "")
+	t.Setenv("UPAAS_SESSION_SECRET", "test-secret")
+	setupViper("upaas")
+
+	cfg, err := buildConfig(slog.Default(), &Params{})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if cfg.HostDataDir != "./data" {
+		t.Errorf("expected HostDataDir ./data, got %q", cfg.HostDataDir)
+	}
+}