Add a standalone server application

Until now I have been running this with Flask in development mode. But
at some point, I would want to deploy it. How do you deploy a Flask
application? Gunicorn or Waitress (behind Nginx) seem like the simplest
options, and Waitress has no dependencies except for the stdlib, so
let's go with it for now.

It has a nice way to run things, I can just add a main in my app.py that
starts Waitress.

Now the only hairy problem to solve is configuration. 12-factor
environment variables look nice at first, but with the Procfile, the Nix
shell with PG* variables, and sometimes people throwing in .env files
too ... in my experience, it ends up being a mess after all. Instead I
think I'll add a simple toml file, and add a default configuration in
the repository that works out of the box for a development checkout.

MANIFEST.in

@@ -0,0 +1,3 @@
+graft hanson/static
+graft hanson/templates
+global-exclude *.pyc

app.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 # Hanson -- Self-hosted prediction market app
 # Copyright 2022 Ruud van Asseldonk
 #
@@ -29,3 +31,38 @@
 @app.errorhandler(NotLoggedInError)  # type: ignore
 def handle_not_logged_in(_: NotLoggedInError) -> Response:
     return Response.redirect_see_other("/login")
+
+
+def main() -> None:
+    """
+    This app.py is designed to run under Flask in development mode, you can run
+    with "python -m flask run". In that case, this main function is not called.
+
+    For a production deployment, we use Waitress as the WSGI server. Then we can
+    start from app.py as the entry point.
+    """
+    import os
+    import waitress
+
+    # TODO: Maybe put this in a config file after all?
+    # The current values are misleading because we don't use those!
+    host = os.getenv("HOST", "0.0.0.0")
+    port = int(os.getenv("PORT", "5000"))
+    pg_host = os.getenv("PGHOST", f"{os.getcwd()}/run/db_dev")
+    pg_database = os.getenv("PGDATABASE", "hanson")
+    pg_user = os.getenv("PGUSER", "hanson_app")
+    pg_password = os.getenv("PGPASSWORD", "hanson_app")
+
+    print("Configuration:")
+    print(f"  BIND={host}")
+    print(f"  PORT={port}")
+    print(f"  PGDATABASE={pg_database}")
+    print(f"  PGUSER={pg_user}")
+    print(f"  PGPASSWORD is not printed here")
+    print(f"  PGHOST={pg_host}")
+    print("Starting server ...")
+    waitress.serve(app, host=host, port=port)
+
+
+if __name__ == "__main__":
+    main()

flake.nix

@@ -16,6 +16,7 @@
         ps.flask
         ps.jinja2
         ps.psycopg2
+        ps.waitress
       ];
       developmentDependencies = ps: [
         # Mypy goes with the pythonPackages, we don't use the top-level pkgs.mypy,
@@ -24,9 +25,26 @@
         ps.mypy
         ps.pytest
       ];
-      python = pkgs.python3.withPackages (ps:
+
+      python = pkgs.python3.override {
+        packageOverrides = self: super: {
+          hanson = self.buildPythonPackage rec {
+            pname = "hanson";
+            version = "0.0.0";
+            src = ./.;
+            propagatedBuildInputs = runtimeDependencies self;
+          };
+        };
+      };
+
+      # For development, we want a Python that has all our dependent packages,
+      # but not Hanson itself as a package.
+      pythonDev = pkgs.python3.withPackages (ps:
         (runtimeDependencies ps) ++ (developmentDependencies ps)
       );
+
+      hanson = python.pkgs.toPythonApplication python.pkgs.hanson;
+
     in
       {
         devShells = {
@@ -38,7 +56,7 @@
               pkgs.overmind
               pkgs.postgresql_14
               pkgs.mkdocs
-              python
+              pythonDev
             ];
 
             LOCALE_ARCHIVE = "${pkgs.glibcLocales}/lib/locale/locale-archive";
@@ -50,7 +68,9 @@
           };
         };
 
-        packages = {};
+        packages = {
+          default = hanson;
+        };
       }
   );
 }

setup.py

@@ -0,0 +1,19 @@
+from setuptools import find_packages, setup
+
+setup(
+    name="hanson",
+    version="0.0.0",
+    packages=find_packages(),
+    include_package_data=True,
+    install_requires=[
+        "click",
+        "flask",
+        "jinja2",
+        "psycopg2",
+        "waitress",
+    ],
+    scripts=[
+        "app.py",
+        "cli.py",
+    ],
+)