Run flask using production wsgi/http server (#185)

Author: daphnegold

app/Dockerfile

@@ -65,7 +65,11 @@ CMD ["poetry", "run", "python", "-m", "src"]
 
 FROM base AS release
 ARG RUN_USER
-WORKDIR /app
+
+# Gunicorn requires this workaround to create writable temporary directory in
+# our readonly root file system. https://github.com/aws/containers-roadmap/issues/736
+RUN mkdir -p /tmp
+VOLUME ["/tmp"]
 
 # TODO(https://github.com/navapbc/template-application-flask/issues/23) Productionize the Docker image
 
@@ -105,4 +109,4 @@ ENV HOST=0.0.0.0
 USER ${RUN_USER}
 
 # Run the application.
-CMD ["poetry", "run", "python", "-m", "src"]
+CMD ["poetry", "run", "gunicorn", "src.app:create_app()"]

app/gunicorn.conf.py

@@ -0,0 +1,25 @@
+"""
+Configuration file for the Gunicorn server used to run the application in production environments.
+
+Attributes:
+    bind(str): The socket to bind. Formatted as '0.0.0.0:$PORT'.
+    workers(int): The number of worker processes for handling requests.
+    threads(int): The number of threads per worker for handling requests.
+
+For more information, see https://docs.gunicorn.org/en/stable/configure.html
+"""
+
+import os
+
+from src.app_config import AppConfig
+
+app_config = AppConfig()
+
+bind = app_config.host + ':' + str(app_config.port)
+# Calculates the number of usable cores and doubles it. Recommended number of workers per core is two.
+# https://docs.gunicorn.org/en/latest/design.html#how-many-workers
+# We use 'os.sched_getaffinity(pid)' not 'os.cpu_count()' because it returns only allowable CPUs.
+# os.sched_getaffinity(pid): Return the set of CPUs the process with PID pid is restricted to.
+# os.cpu_count(): Return the number of CPUs in the system.
+workers = len(os.sched_getaffinity(0)) * 2
+threads = 4

app/poetry.lock

@@ -19,6 +19,7 @@ pytz = "^2022.2.1"
 APIFlask = "^1.1.3"
 marshmallow-dataclass = {extras = ["enum", "union"], version = "^8.5.8"}
 marshmallow = "^3.18.0"
+gunicorn = "^21.2.0"
 
 [tool.poetry.group.dev.dependencies]
 black = "^22.6.0"
@@ -42,7 +43,6 @@ requires = ["poetry-core>=1.0.0"]
 build-backend = "poetry.core.masonry.api"
 
 [tool.poetry.scripts]
-app-start = "src.__main__:main"
 db-migrate = "src.db.migrations.run:up"
 db-migrate-down = "src.db.migrations.run:down"
 db-migrate-down-all = "src.db.migrations.run:downall"

app/pyproject.toml

@@ -2,8 +2,6 @@
 
 
 class AppConfig(PydanticBaseEnvConfig):
-    environment: str = "prod"
-
     # Set HOST to 127.0.0.1 by default to avoid other machines on the network
     # from accessing the application. This is especially important if you are
     # running the application locally on a public network. This needs to be

app/src/__main__.py

@@ -20,6 +20,7 @@ services:
       args:
         - RUN_UID=${RUN_UID:-4000}
         - RUN_USER=${RUN_USER:-app}
+    command: ["poetry", "run", "flask", "--app", "src.app", "run", "--host", "0.0.0.0", "--port", "8080", "--reload"]
     container_name: main-app
     env_file: ./app/local.env
     ports:

app/src/app_config.py

@@ -4,7 +4,7 @@ This document describes the best practices and patterns for how the application
 
 ## Client Initialization and Configuration
 
-The database client is initialized when the application starts (see [src/\_\_main\_\_.py](../../../app/src/__main__.py). As the database engine that is used to create acquire connections to the database is initialized using the database configuration defined in [db_config.py](../../../app/src/db/db_config.py), which is configured through environment variables. The initialized database client is then stored on the Flask app's [\`extensions\` dictionary](https://flask.palletsprojects.com/en/2.2.x/src/#flask.Flask.extensions) to be used throughout the lifetime of the application.
+The database client is initialized when the application starts (see [src/\_\_main\_\_.py](../../../app/src/app.py). The database engine that is used to create acquire connections to the database is initialized using the database configuration defined in [db_config.py](../../../app/src/db/db_config.py), which is configured through environment variables. The initialized database client is then stored on the Flask app's [\`extensions\` dictionary](https://flask.palletsprojects.com/en/2.2.x/src/#flask.Flask.extensions) to be used throughout the lifetime of the application.
 
 ## Session Management