Load gunicorn defaults before overriding with app settings

fixes: #4917

CHANGES/4917.feature

@@ -0,0 +1 @@
+Enabled the gunicorn applications for ``pulpcore-api`` and ``pulpcore-content`` to load configurations from the "gunicorn.conf.py" file.

pulpcore/app/entrypoint.py

@@ -9,9 +9,9 @@
 from django.db import connection
 from django.db.utils import InterfaceError, OperationalError
 from gunicorn.workers.sync import SyncWorker
-from gunicorn.app.base import BaseApplication
 
 from pulpcore.app.apps import pulp_plugin_configs
+from pulpcore.app.pulpcore_gunicorn_application import PulpcoreGunicornApplication
 
 logger = getLogger(__name__)
 
@@ -80,19 +80,14 @@ def run(self):
                 self.api_app_status.delete()
 
 
-class PulpcoreApiApplication(BaseApplication):
-    def __init__(self, options):
-        self.options = options or {}
-        super().__init__()
-
-    def load_config(self):
-        [
-            self.cfg.set(key.lower(), value)
-            for key, value in self.options.items()
-            if value is not None
-        ]
-        self.cfg.set("default_proc_name", "pulpcore-api")
-        self.cfg.set("worker_class", PulpApiWorker.__module__ + "." + PulpApiWorker.__qualname__)
+class PulpcoreApiApplication(PulpcoreGunicornApplication):
+    def load_app_specific_config(self):
+        self.set_option("default_proc_name", "pulpcore-api", enforced=True)
+        self.set_option(
+            "worker_class",
+            PulpApiWorker.__module__ + "." + PulpApiWorker.__qualname__,
+            enforced=True,
+        )
 
     def load(self):
         using_pulp_api_worker.set(True)

pulpcore/app/pulpcore_gunicorn_application.py

@@ -0,0 +1,71 @@
+import sys
+
+from gunicorn.app.base import Application
+
+
+class PulpcoreGunicornApplication(Application):
+    """
+    A common class for the api and content applications to inherit from that loads the default
+    gunicorn configs (including from a config file if one exists) and then overrides with the values
+    specified in the init scripts. With warnings / errors if the user overrides something that won't
+    take effect or cannot be changed.
+    """
+
+    def __init__(self, options):
+        self.options = options or {}
+        super().__init__()
+
+    def init(self, *args, **kwargs):
+        """
+        A hook for setting application-specific configs, which we instead do below in load_config
+        where it's non-overridable.
+        """
+        pass
+
+    def set_option(self, key, value, enforced=False):
+        if value is None:  # not specified by init script
+            return
+
+        def _is_default(key, value):
+            if value is None:
+                return True
+            defaults = {
+                "default_proc_name": "gunicorn",
+                "reload_extra_files": [],
+                "access_log_format": '%(h)s %(l)s %(u)s %(t)s "%(r)s" %(s)s %(b)s "%(f)s" "%(a)s"',
+                "bind": ["127.0.0.1:8000"],
+                "threads": 1,
+                "worker_class": "<class 'gunicorn.workers.sync.SyncWorker'>",
+            }
+            return key in defaults and str(defaults[key]) == str(value)
+
+        current_value = getattr(self.cfg, key, None)
+        if not _is_default(key, current_value) and str(current_value) != str(value):
+            if enforced:
+                sys.stderr.write(
+                    f"Error: {key} is set to {current_value} in gunicorn.conf.py but must not be "
+                    "changed!\n"
+                )
+                exit(1)
+            else:
+                sys.stderr.write(
+                    f"Warning: {key} is set to {current_value} in gunicorn.conf.py but is "
+                    f"overridden to {value} by init script!\n"
+                )
+
+        self.cfg.set(key, value)
+
+    def load_config(self):
+        # Load default gunicorn configs, including reading from the default config file.
+        super().load_config()
+        # Override with settings that we've specified in the startup script.
+        for key, value in self.options.items():
+            self.set_option(key, value)
+        self.set_option("threads", "1", enforced=True)
+        self.load_app_specific_config()
+
+    def load_app_specific_config(self):
+        raise NotImplementedError
+
+    def load(self):
+        raise NotImplementedError

pulpcore/content/entrypoint.py

@@ -1,20 +1,11 @@
 import click
-from gunicorn.app.base import BaseApplication
+from pulpcore.app.pulpcore_gunicorn_application import PulpcoreGunicornApplication
 
 
-class PulpcoreContentApplication(BaseApplication):
-    def __init__(self, options):
-        self.options = options or {}
-        super().__init__()
-
-    def load_config(self):
-        [
-            self.cfg.set(key.lower(), value)
-            for key, value in self.options.items()
-            if value is not None
-        ]
-        self.cfg.set("default_proc_name", "pulpcore-content")
-        self.cfg.set("worker_class", "aiohttp.GunicornWebWorker")
+class PulpcoreContentApplication(PulpcoreGunicornApplication):
+    def load_app_specific_config(self):
+        self.set_option("default_proc_name", "pulpcore-content", enforced=True)
+        self.set_option("worker_class", "aiohttp.GunicornWebWorker", enforced=True)
 
     def load(self):
         import pulpcore.content