Add docker-compose.yml for deploying upaas (closes #223)

The compose file builds the image from this repo, mounts the Docker
socket and HOST_DATA_DIR (passed to upaas as UPAAS_HOST_DATA_DIR),
reads settings from .env, and restarts unless stopped. The port is
published on 127.0.0.1 only, for a TLS-terminating proxy in front, and
UPAAS_PLAINTEXT_HTTP is left unset. A healthcheck against /health uses
the runtime image's busybox wget.

The README's plain-HTTP Compose example becomes a short deploy section
that points at the file. .env is added to .dockerignore so settings are
not copied into the build.

Model: opus-5-5

README.md

@@ -229,16 +229,15 @@ settings from a `.env` file next to it, which needs at least:
 HOST_DATA_DIR=/srv/upaas/data
 ```
 
-Other settings from [Configuration](#configuration) go in the same file, except
-`PORT`: the compose file sets it to 8080, overriding `.env`, to match its port
-mapping and healthcheck. Then run `docker compose up -d` from the repo root;
-`docker compose ps` shows the container as healthy once `/health` answers.
+Other settings from [Configuration](#configuration) go in the same file. Then
+run `docker compose up -d` from the repo root; `docker compose ps` shows the
+container as healthy once `/health` answers.
 
 **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`.
+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.
 
 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.

TODO.md

@@ -23,8 +23,7 @@ regress.
 - 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).
+  replaced by a short deploy section (#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

docker-compose.yml

@@ -7,9 +7,6 @@ services:
     # 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"
       # 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}

internal/config/config.go

@@ -32,12 +32,6 @@ 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
@@ -130,10 +124,6 @@ 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

@@ -1,33 +0,0 @@
-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)
-	}
-}