feat: fastapi-framework init profile and extension (#1868)

This PR implements the spec ISD160 - 12-Factor FastAPI Support" for
charmcraft.

For that, a new init profile called "fastapi-framework" and a new
fastapi extension, called "fastapi-framework" are needed. These
additions are similar to the flask and django init profiles and
extensions.

For the fastapi profile, the base 24.04 is used.

---------

Co-authored-by: Alex Lowe <alex.lowe@canonical.com>

charmcraft/application/commands/init.py

@@ -39,6 +39,7 @@
     "flask-framework": "init-flask-framework",
     "django-framework": "init-django-framework",
     "go-framework": "init-go-framework",
+    "fastapi-framework": "init-fastapi-framework",
 }
 DEFAULT_PROFILE = "simple"
 

charmcraft/extensions/__init__.py

@@ -17,7 +17,12 @@
 """Extension processor and related utilities."""
 
 from charmcraft.extensions._utils import apply_extensions
-from charmcraft.extensions.app import DjangoFramework, FlaskFramework, GoFramework
+from charmcraft.extensions.app import (
+    DjangoFramework,
+    FastAPIFramework,
+    FlaskFramework,
+    GoFramework,
+)
 from charmcraft.extensions.extension import Extension
 from charmcraft.extensions.registry import (
     get_extension_class,
@@ -42,3 +47,4 @@
 register("flask-framework", FlaskFramework)
 register("django-framework", DjangoFramework)
 register("go-framework", GoFramework)
+register("fastapi-framework", FastAPIFramework)

charmcraft/extensions/app.py

@@ -314,3 +314,56 @@ def get_image_name(self) -> str:
     def get_container_name(self) -> str:
         """Return name of the container for the app image."""
         return "app"
+
+
+class FastAPIFramework(_AppBase):
+    """Extension for 12-factor FastAPI applications."""
+
+    framework = "fastapi"
+    options = {
+        "webserver-workers": {
+            "type": "int",
+            "default": 1,
+            "description": "Number of workers for uvicorn. Sets env variable WEB_CONCURRENCY. See https://www.uvicorn.org/#command-line-options.",
+        },
+        "webserver-port": {
+            "type": "int",
+            "default": 8080,
+            "description": "Bind to a socket with this port. Default: 8000. Sets env variable  UVICORN_PORT.",
+        },
+        "webserver-log-level": {
+            "type": "string",
+            "default": "info",
+            "description": "Set the log level. Options: 'critical', 'error', 'warning', 'info', 'debug', 'trace'. Sets the env variable UVICORN_LOG_LEVEL.",
+        },
+        "metrics-port": {
+            "type": "int",
+            "default": 8080,
+            "description": "Port where the prometheus metrics will be scraped.",
+        },
+        "metrics-path": {
+            "type": "string",
+            "default": "/metrics",
+            "description": "Path where the prometheus metrics will be scraped.",
+        },
+        "app-secret-key": {
+            "type": "string",
+            "description": "Long secret you can use for sessions, csrf or any other thing where you need a random secret shared by all units",
+        },
+    }
+
+    @staticmethod
+    @override
+    def get_supported_bases() -> list[tuple[str, str]]:
+        """Return supported bases."""
+        return [("ubuntu", "24.04")]
+
+    @override
+    def get_image_name(self) -> str:
+        """Return name of the app image."""
+        return "app-image"
+
+    @override
+    def get_container_name(self) -> str:
+        """Return name of the container for the app image."""
+        return "app"

charmcraft/templates/init-fastapi-framework/.gitignore.j2

@@ -0,0 +1,9 @@
+venv/
+build/
+*.charm
+.tox/
+.coverage
+__pycache__/
+*.py[cod]
+.idea
+.vscode/

charmcraft/templates/init-fastapi-framework/charmcraft.yaml.j2

@@ -0,0 +1,59 @@
+# This file configures Charmcraft.
+# See https://juju.is/docs/sdk/charmcraft-config for guidance.
+
+name: {{ name }}
+
+type: charm
+
+base: ubuntu@24.04
+
+# the platforms this charm should be built on and run on.
+# you can check your architecture with `dpkg --print-architecture`
+platforms:
+  amd64:
+  # arm64:
+  # ppc64el:
+  # s390x:
+
+# (Required)
+summary: A very short one-line summary of the FastAPI application.
+
+# (Required)
+description: |
+  A comprehensive overview of your FastAPI application.
+
+extensions:
+  - fastapi-framework
+
+# Uncomment the integrations used by your application
+# Integrations set to "optional: false" will block the charm
+# until the applications are integrated.
+# requires:
+#   mysql:
+#     interface: mysql_client
+#     optional: false
+#     limit: 1
+#   postgresql:
+#     interface: postgresql_client
+#     optional: false
+#     limit: 1
+#   mongodb:
+#     interface: mongodb_client
+#     optional: false
+#     limit: 1
+#   redis:
+#     interface: redis
+#     optional: false
+#     limit: 1
+#   s3:
+#     interface: s3
+#     optional: false
+#     limit: 1
+#   saml:
+#     interface: saml
+#     optional: false
+#     limit: 1
+#   rabbitmq:
+#     interface: rabbitmq
+#     optional: false
+#     limit: 1

charmcraft/templates/init-fastapi-framework/requirements.txt.j2

@@ -0,0 +1 @@
+paas-app-charmer==1.*

charmcraft/templates/init-fastapi-framework/src/charm.py.j2

@@ -0,0 +1,30 @@
+#!/usr/bin/env python3
+# Copyright {{ year }} {{ author }}
+# See LICENSE file for licensing details.
+
+"""FastAPI Charm entrypoint."""
+
+import logging
+import typing
+
+import ops
+
+import paas_app_charmer.fastapi
+
+logger = logging.getLogger(__name__)
+
+
+class {{ class_name }}(paas_app_charmer.fastapi.Charm):
+    """FastAPI Charm service."""
+
+    def __init__(self, *args: typing.Any) -> None:
+        """Initialize the instance.
+
+        Args:
+            args: passthrough to CharmBase.
+        """
+        super().__init__(*args)
+
+
+if __name__ == "__main__":
+    ops.main.main({{ class_name }})

tests/extensions/test_app.py

@@ -19,6 +19,7 @@
 from charmcraft.extensions import apply_extensions
 from charmcraft.extensions.app import (
     DjangoFramework,
+    FastAPIFramework,
     FlaskFramework,
     GoFramework,
 )
@@ -178,14 +179,20 @@ def flask_input_yaml_fixture():
                 "name": "test-go",
                 "summary": "test summary",
                 "description": "test description",
-                "bases": [{"name": "ubuntu", "channel": "24.04"}],
+                "base": "ubuntu@24.04",
+                "platforms": {
+                    "amd64": None,
+                },
                 "extensions": ["go-framework"],
             },
             True,
             {
                 "actions": GoFramework.actions,
                 "assumes": ["k8s-api"],
-                "bases": [{"channel": "24.04", "name": "ubuntu"}],
+                "base": "ubuntu@24.04",
+                "platforms": {
+                    "amd64": None,
+                },
                 "containers": {
                     "app": {"resource": "app-image"},
                 },
@@ -232,6 +239,72 @@ def flask_input_yaml_fixture():
                 "type": "charm",
             },
         ),
+        (
+            {
+                "type": "charm",
+                "name": "test-fastapi",
+                "summary": "test summary",
+                "description": "test description",
+                "base": "ubuntu@24.04",
+                "platforms": {
+                    "amd64": None,
+                },
+                "extensions": ["fastapi-framework"],
+            },
+            True,
+            {
+                "actions": FastAPIFramework.actions,
+                "assumes": ["k8s-api"],
+                "base": "ubuntu@24.04",
+                "platforms": {
+                    "amd64": None,
+                },
+                "containers": {
+                    "app": {"resource": "app-image"},
+                },
+                "description": "test description",
+                "name": "test-fastapi",
+                "charm-libs": [
+                    {"lib": "traefik_k8s.ingress", "version": "2"},
+                    {"lib": "observability_libs.juju_topology", "version": "0"},
+                    {"lib": "grafana_k8s.grafana_dashboard", "version": "0"},
+                    {"lib": "loki_k8s.loki_push_api", "version": "0"},
+                    {"lib": "data_platform_libs.data_interfaces", "version": "0"},
+                    {"lib": "prometheus_k8s.prometheus_scrape", "version": "0"},
+                    {"lib": "redis_k8s.redis", "version": "0"},
+                    {"lib": "data_platform_libs.s3", "version": "0"},
+                    {"lib": "saml_integrator.saml", "version": "0"},
+                ],
+                "config": {
+                    "options": {**FastAPIFramework.options},
+                },
+                "parts": {
+                    "charm": {
+                        "plugin": "charm",
+                        "source": ".",
+                        "build-snaps": ["rustup"],
+                        "override-build": "rustup default stable\ncraftctl default",
+                    }
+                },
+                "peers": {"secret-storage": {"interface": "secret-storage"}},
+                "provides": {
+                    "metrics-endpoint": {"interface": "prometheus_scrape"},
+                    "grafana-dashboard": {"interface": "grafana_dashboard"},
+                },
+                "requires": {
+                    "logging": {"interface": "loki_push_api"},
+                    "ingress": {"interface": "ingress", "limit": 1},
+                },
+                "resources": {
+                    "app-image": {
+                        "description": "fastapi application image.",
+                        "type": "oci-image",
+                    },
+                },
+                "summary": "test summary",
+                "type": "charm",
+            },
+        ),
     ],
 )
 def test_apply_extensions_correct(monkeypatch, experimental, tmp_path, input_yaml, expected):

tests/spread/commands/init-flask-framework/task.yaml → tests/spread/commands/init-extensions/task.yaml

@@ -1,9 +1,15 @@
-summary: test charmcraft init with flask-framework profile
+summary: test charmcraft init with framework profiles
 priority: 500  # This builds pydantic, so do it early
 kill-timeout: 75m  # Because it builds pydantic, it takes a long time.
 systems:
   # We only need to run this test once, and it takes a long time.
   - ubuntu-22.04-64
+environment:
+  PROFILE/flask: flask-framework
+  PROFILE/django: django-framework
+  PROFILE/go: go-framework
+  PROFILE/fastapi: fastapi-framework
+  CHARMCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS: "true"
 
 execute: |
   # Required for fetch-libs to succeed since the libraries are not available on
@@ -14,7 +20,7 @@ execute: |
 
   mkdir -p test-init
   cd test-init
-  charmcraft init --profile flask-framework
+  charmcraft init --profile "${PROFILE}"
   charmcraft fetch-libs
   charmcraft pack --verbose
   test -f *.charm