Supporting running FastAPI apps via Uvicorn in Python runtimes

.gitignore

@@ -7,6 +7,9 @@
 *.userosscache
 *.sln.docstates
 
+# .NET global.json file to set the SDK version per user
+global.json
+
 # User-specific files (MonoDevelop/Xamarin Studio)
 *.userprefs
 

images/runtime/python/3.10/bullseye.Dockerfile

@@ -81,6 +81,7 @@ LABEL io.buildpacks.stack.id="oryx.stacks.skeleton"
 RUN ${IMAGES_DIR}/runtime/python/install-dependencies.sh
 RUN pip install --upgrade pip \
     && pip install gunicorn \
+    && pip install uvicorn \
     && pip install debugpy \
     && pip install viztracer==0.15.6 \
     && pip install vizplugins==0.1.3 \

images/runtime/python/3.11/bullseye.Dockerfile

@@ -81,6 +81,7 @@ LABEL io.buildpacks.stack.id="oryx.stacks.skeleton"
 RUN ${IMAGES_DIR}/runtime/python/install-dependencies.sh
 RUN pip install --upgrade pip \
     && pip install gunicorn \
+    && pip install uvicorn \
     && pip install debugpy \
     && pip install viztracer==0.15.6 \
     && pip install vizplugins==0.1.3 \

images/runtime/python/3.7/bullseye.Dockerfile

@@ -81,6 +81,7 @@ LABEL io.buildpacks.stack.id="oryx.stacks.skeleton"
 RUN ${IMAGES_DIR}/runtime/python/install-dependencies.sh
 RUN pip install --upgrade pip \
     && pip install gunicorn \
+    && pip install uvicorn \
     && pip install debugpy \
     && pip install viztracer==0.15.6 \
     && pip install vizplugins==0.1.3 \

images/runtime/python/3.8/bullseye.Dockerfile

@@ -81,6 +81,7 @@ LABEL io.buildpacks.stack.id="oryx.stacks.skeleton"
 RUN ${IMAGES_DIR}/runtime/python/install-dependencies.sh
 RUN pip install --upgrade pip \
     && pip install gunicorn \
+    && pip install uvicorn \
     && pip install debugpy \
     && pip install viztracer==0.15.6 \
     && pip install vizplugins==0.1.3 \

images/runtime/python/template.Dockerfile

@@ -83,6 +83,7 @@ LABEL io.buildpacks.stack.id="oryx.stacks.skeleton"
 RUN ${IMAGES_DIR}/runtime/python/install-dependencies.sh
 RUN pip install --upgrade pip \
     && pip install gunicorn \
+    && pip install uvicorn \
     && pip install debugpy \
     && pip install viztracer==0.15.6 \
     && pip install vizplugins==0.1.3 \

src/startupscriptgenerator/src/python/frameworks.go

@@ -6,46 +6,125 @@
 package main
 
 import (
+	"bufio"
 	"common"
+	"fmt"
 	"io/ioutil"
+	"os"
 	"path/filepath"
-	"fmt"
+	"strings"
 )
 
 type PyAppFramework interface {
-    Name() string
-    GetGunicornModuleArg() string
-    GetDebuggableModule() string
-    detect() bool
+	Name() string
+	GetGunicornModuleArg() string
+	GetUvicornModuleArg() string
+	GetDebuggableModule() string
+	detect() bool
 }
 
 type djangoDetector struct {
-	appPath		string
-	venvName	string
-	wsgiModule	string
+	appPath    string
+	venvName   string
+	wsgiModule string
 }
 
 type flaskDetector struct {
-	appPath		string
-	mainFile	string
+	appPath  string
+	mainFile string
+}
+
+type fastApiDetector struct {
+	appPath    string
+	mainFile   string
+	launchPath string
 }
 
 func DetectFramework(appPath string, venvName string) PyAppFramework {
 	var detector PyAppFramework
 
-	detector = &djangoDetector{ appPath: appPath, venvName: venvName }
+	detector = &fastApiDetector{appPath: appPath}
+	if detector.detect() {
+		return detector
+	}
+
+	detector = &djangoDetector{appPath: appPath, venvName: venvName}
 	if detector.detect() {
 		return detector
 	}
 
-	detector = &flaskDetector{ appPath: appPath }
+	detector = &flaskDetector{appPath: appPath}
 	if detector.detect() {
 		return detector
 	}
 
 	return nil
 }
 
+func (detector *fastApiDetector) Name() string {
+	return "FastAPI"
+}
+
+// Checks if the app is based on FastAPI
+func (detector *fastApiDetector) detect() bool {
+	logger := common.GetLogger("python.frameworks.fastApiDetector.detect")
+	defer logger.Shutdown()
+
+	filesToSearch := []string{"app.py", "main.py"}
+
+	for _, file := range filesToSearch {
+		fullPath := filepath.Join(detector.appPath, file)
+		if common.FileExists(fullPath) {
+			// Match on something that looks like the following in the main file:
+			//	app = FastAPI()
+			//	app = fastapi.FastAPI()
+			//	app = FastAPI(
+			f, err := os.Open(fullPath)
+			if err != nil {
+				logger.LogWarning("Failed to open and read file %s for FastAPI detection: %s", fullPath, err.Error())
+				continue
+			}
+
+			defer f.Close()
+
+			scanner := bufio.NewScanner(f)
+			for scanner.Scan() {
+				if strings.Contains(scanner.Text(), "FastAPI(") {
+					decl := strings.Split(scanner.Text(), " ")
+					if len(decl) >= 3 && decl[1] == "=" {
+						detector.mainFile = fullPath
+						mainObjName := decl[0]
+						relativePath, err := filepath.Rel(detector.appPath, fullPath)
+						if err != nil {
+							continue
+						}
+
+						// dir1/dir2/main.py -> dir1.dir2.main
+						mainPath := strings.ReplaceAll(strings.TrimSuffix(relativePath, ".py"), "/", ".")
+
+						detector.launchPath = fmt.Sprintf("%s:%s", mainPath, mainObjName)
+						return true
+					}
+				}
+			}
+		}
+	}
+
+	return false
+}
+
+func (detector *fastApiDetector) GetGunicornModuleArg() string {
+	return ""
+}
+
+func (detector *fastApiDetector) GetUvicornModuleArg() string {
+	return detector.launchPath
+}
+
+func (detector *fastApiDetector) GetDebuggableModule() string {
+	return ""
+}
+
 func (detector *djangoDetector) Name() string {
 	return "Django"
 }
@@ -81,6 +160,10 @@ func (detector *djangoDetector) GetGunicornModuleArg() string {
 	return detector.wsgiModule
 }
 
+func (detector *djangoDetector) GetUvicornModuleArg() string {
+	return ""
+}
+
 func (detector *djangoDetector) GetDebuggableModule() string {
 	if !common.FileExists(filepath.Join(detector.appPath, "manage.py")) {
 		logger := common.GetLogger("python.frameworks.djangoDetector.GetDebuggableModule")
@@ -122,10 +205,14 @@ func (detector *flaskDetector) detect() bool {
 
 // TODO: detect correct variable name from a list of common names (app, application, etc.)
 func (detector *flaskDetector) GetGunicornModuleArg() string {
-	module := detector.mainFile[0 : len(detector.mainFile) - 3] // Remove the '.py' from the end
+	module := detector.mainFile[0 : len(detector.mainFile)-3] // Remove the '.py' from the end
 	return module + ":app"
 }
 
+func (detector *flaskDetector) GetUvicornModuleArg() string {
+	return ""
+}
+
 func (detector *flaskDetector) GetDebuggableModule() string {
 	if !common.FileExists(filepath.Join(detector.appPath, "wsgi.py")) &&
 		!common.FileExists(filepath.Join(detector.appPath, "app.py")) {

src/startupscriptgenerator/src/python/scriptgenerator.go

@@ -87,7 +87,8 @@ func (gen *PythonStartupScriptGenerator) GenerateEntrypointScript() string {
 	appType := ""         // "Django", "Flask", etc.
 	appDebugAdapter := "" // Used debugger adapter
 	appDirectory := ""
-	appModule := ""      // Suspected entry module in app
+	gunicornModule := "" // Gunicorn entry module in app
+	uvicornModule := ""  // Uvicorn entry module in app
 	appDebugModule := "" // Command to run under a debugger in case debugging mode was requested
 
 	command := gen.UserStartupCommand // A custom command takes precedence over any framework defaults
@@ -102,18 +103,19 @@ func (gen *PythonStartupScriptGenerator) GenerateEntrypointScript() string {
 			println("Detected an app based on " + appFw.Name())
 			appType = appFw.Name()
 			appDirectory = gen.getAppPath()
-			appModule = appFw.GetGunicornModuleArg()
+			gunicornModule = appFw.GetGunicornModuleArg()
+			uvicornModule = appFw.GetUvicornModuleArg()
 			appDebugModule = appFw.GetDebuggableModule()
 		} else {
 			println("No framework detected; using default app from " + gen.DefaultAppPath)
 			logger.LogInformation("Using default app.")
 			appType = "Default"
 			appDirectory = gen.DefaultAppPath
-			appModule = gen.DefaultAppModule
+			gunicornModule = gen.DefaultAppModule
 			appDebugModule = gen.DefaultAppDebugModule
 		}
 
-		if appModule != "" {
+		if gunicornModule != "" || uvicornModule != "" {
 			// Patch all legacy ptvsd debug adaptor calls to debugpy
 			if gen.DebugAdapter == "ptvsd" {
 				gen.DebugAdapter = "debugpy"
@@ -128,10 +130,14 @@ func (gen *PythonStartupScriptGenerator) GenerateEntrypointScript() string {
 				}
 
 				appDebugAdapter = gen.DebugAdapter
+			} else if uvicornModule != "" {
+				logger.LogInformation(fmt.Sprintf("Generating Uvicorn startup command for module '%s'.", uvicornModule))
+				println(fmt.Sprintf(GeneratingCommandMessage, "uvicorn", uvicornModule))
+				command = gen.buildUvicornCommandForModule(uvicornModule, appDirectory)
 			} else {
-				logger.LogInformation("Generating command for appModule.")
-				println(fmt.Sprintf(GeneratingCommandMessage, "gunicorn", appModule))
-				command = gen.buildGunicornCommandForModule(appModule, appDirectory)
+				logger.LogInformation(fmt.Sprintf("Generating Gunicorn startup command for module '%s'.", gunicornModule))
+				println(fmt.Sprintf(GeneratingCommandMessage, "gunicorn", gunicornModule))
+				command = gen.buildGunicornCommandForModule(gunicornModule, appDirectory)
 			}
 		}
 	}
@@ -141,7 +147,7 @@ func (gen *PythonStartupScriptGenerator) GenerateEntrypointScript() string {
 	logger.LogProperties(
 		"Finalizing script",
 		map[string]string{"appType": appType, "appDebugAdapter": appDebugAdapter,
-			"appModule": appModule, "venv": gen.Manifest.VirtualEnvName})
+			"gunicornModule": gunicornModule, "uvicornModule": uvicornModule, "venv": gen.Manifest.VirtualEnvName})
 
 	var runScript = scriptBuilder.String()
 	return runScript
@@ -277,10 +283,10 @@ func (gen *PythonStartupScriptGenerator) buildGunicornCommandForModule(module st
 	args := "--timeout 600 --access-logfile '-' --error-logfile '-'"
 
 	pythonUseGunicornConfigFromPath := os.Getenv(consts.PythonGunicornConfigPathEnvVarName)
-	if pythonUseGunicornConfigFromPath != ""  {
-		args = appendArgs(args, "-c "+pythonUseGunicornConfigFromPath)		
+	if pythonUseGunicornConfigFromPath != "" {
+		args = appendArgs(args, "-c "+pythonUseGunicornConfigFromPath)
 	}
-	
+
 	pythonEnableGunicornMultiWorkers := common.GetBooleanEnvironmentVariable(consts.PythonEnableGunicornMultiWorkersEnvVarName)
 
 	if pythonEnableGunicornMultiWorkers {
@@ -290,15 +296,15 @@ func (gen *PythonStartupScriptGenerator) buildGunicornCommandForModule(module st
 		pythonCustomWorkerNum := os.Getenv(consts.PythonGunicornCustomWorkerNum)
 		pythonCustomThreadNum := os.Getenv(consts.PythonGunicornCustomThreadNum)
 		workers := ""
-		if (pythonCustomWorkerNum != "") {
+		if pythonCustomWorkerNum != "" {
 			workers = pythonCustomWorkerNum
 		} else {
 			workers = strconv.Itoa((2 * runtime.NumCPU()) + 1)
 			// 2N+1 number of workers is recommended by Gunicorn docs.
 			// Where N is the number of CPU threads.
 		}
 		args = appendArgs(args, "--workers="+workers)
-		if (pythonCustomThreadNum != "") {
+		if pythonCustomThreadNum != "" {
 			args = appendArgs(args, "--threads="+pythonCustomThreadNum)
 		}
 	}
@@ -318,6 +324,12 @@ func (gen *PythonStartupScriptGenerator) buildGunicornCommandForModule(module st
 	return "gunicorn " + module
 }
 
+// Produces the uvicorn command to run the app.
+// `module` is of the pattern "<dotted module path>:<variable name>".
+func (gen *PythonStartupScriptGenerator) buildUvicornCommandForModule(module string, appDir string) string {
+	return fmt.Sprintf("uvicorn %s --port $PORT --host $HOST", module)
+}
+
 func (gen *PythonStartupScriptGenerator) shouldStartAppInDebugMode() bool {
 	logger := common.GetLogger("python.scriptgenerator.shouldStartAppInDebugMode")
 	defer logger.Shutdown()