[release/13.0] Generate fallback Dockerfile for Python apps without UV (#12640)

* Initial plan

* Add fallback Dockerfile generation for Python apps without UV support

- Modified PythonAppResourceBuilderExtensions to generate Dockerfiles for all Python apps
- Split Dockerfile generation into two methods: GenerateUvDockerfile and GenerateFallbackDockerfile
- Fallback Dockerfiles detect requirements.txt and run pip install if present
- Uses same runtime image (python:X.Y-slim-bookworm) as UV workflow for consistency
- Updated PythonVersionDetector to accept nullable VirtualEnvironment parameter
- Added comprehensive tests for fallback Dockerfile generation

Co-authored-by: davidfowl <[email protected]>

* Address code review feedback: simplify version detection logic and remove empty line

Co-authored-by: davidfowl <[email protected]>

* PR feedback

* Use a default Python version if we can't detect it.

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: davidfowl <[email protected]>
Co-authored-by: Eric Erhardt <[email protected]>

Author: 4 people

src/Aspire.Hosting.Python/PythonAppResourceBuilderExtensions.cs

@@ -14,7 +14,7 @@ internal static partial class PythonVersionDetector
     /// <param name="appDirectory">The directory containing the Python application.</param>
     /// <param name="virtualEnvironment">The virtual environment to check as a fallback.</param>
     /// <returns>The detected Python version in major.minor format (e.g., "3.13"), or null if not found.</returns>
-    public static string? DetectVersion(string appDirectory, VirtualEnvironment virtualEnvironment)
+    public static string? DetectVersion(string appDirectory, VirtualEnvironment? virtualEnvironment)
     {
         // First, try .python-version file (most specific)
         var pythonVersionFile = Path.Combine(appDirectory, ".python-version");
@@ -41,7 +41,12 @@ internal static partial class PythonVersionDetector
         }
 
         // Third, try detecting from virtual environment as ultimate fallback
-        return DetectVersionFromVirtualEnvironment(virtualEnvironment);
+        if (virtualEnvironment != null)
+        {
+            return DetectVersionFromVirtualEnvironment(virtualEnvironment);
+        }
+
+        return null;
     }
 
     /// <summary>

src/Aspire.Hosting.Python/PythonVersionDetector.cs

@@ -1372,5 +1372,157 @@ public async Task WithUvEnvironment_CustomBaseImages_GeneratesDockerfileWithCust
         // Verify the custom runtime image is used
         Assert.Contains("FROM python:3.13-slim AS app", dockerfileContent);
     }
+
+    [Fact]
+    public async Task FallbackDockerfile_GeneratesDockerfileWithoutUv_WithRequirementsTxt()
+    {
+        using var sourceDir = new TempDirectory();
+        using var outputDir = new TempDirectory();
+        var projectDirectory = sourceDir.Path;
+
+        // Create a Python project without UV but with requirements.txt
+        var requirementsContent = """
+            flask==3.0.0
+            requests==2.31.0
+            """;
+
+        var scriptContent = """
+            print("Hello from non-UV project!")
+            """;
+
+        File.WriteAllText(Path.Combine(projectDirectory, "requirements.txt"), requirementsContent);
+        File.WriteAllText(Path.Combine(projectDirectory, "main.py"), scriptContent);
+
+        using var builder = TestDistributedApplicationBuilder.Create(DistributedApplicationOperation.Publish, outputDir.Path, step: "publish-manifest");
+
+        // Add Python resources without UV environment
+        builder.AddPythonScript("script-app", projectDirectory, "main.py");
+
+        var app = builder.Build();
+        app.Run();
+
+        // Verify that Dockerfile was generated
+        var dockerfilePath = Path.Combine(outputDir.Path, "script-app.Dockerfile");
+        Assert.True(File.Exists(dockerfilePath), "Dockerfile should be generated for non-UV Python app");
+
+        var dockerfileContent = File.ReadAllText(dockerfilePath);
+
+        // Verify it's a fallback Dockerfile (single stage, no UV)
+        Assert.DoesNotContain("uv sync", dockerfileContent);
+        Assert.DoesNotContain("ghcr.io/astral-sh/uv", dockerfileContent);
+
+        // Verify it uses pip install for requirements.txt
+        Assert.Contains("pip install --no-cache-dir -r requirements.txt", dockerfileContent);
+
+        // Verify it uses the same runtime image as UV workflow
+        Assert.Contains("FROM python:3.13-slim-bookworm", dockerfileContent);
+
+        await Verify(dockerfileContent);
+    }
+
+    [Fact]
+    public async Task FallbackDockerfile_GeneratesDockerfileWithoutUv_WithoutRequirementsTxt()
+    {
+        using var sourceDir = new TempDirectory();
+        using var outputDir = new TempDirectory();
+        var projectDirectory = sourceDir.Path;
+
+        // Create a Python project without UV and without requirements.txt
+        var scriptContent = """
+            print("Hello from non-UV project with no dependencies!")
+            """;
+
+        var pyprojectContent = """
+            [project]
+            name = "test-app"
+            version = "0.1.0"
+            requires-python = ">=3.11"
+            """;
+
+        File.WriteAllText(Path.Combine(projectDirectory, "main.py"), scriptContent);
+        File.WriteAllText(Path.Combine(projectDirectory, "pyproject.toml"), pyprojectContent);
+
+        using var builder = TestDistributedApplicationBuilder.Create(DistributedApplicationOperation.Publish, outputDir.Path, step: "publish-manifest");
+
+        // Add Python resources without UV environment
+        builder.AddPythonScript("script-app", projectDirectory, "main.py");
+
+        var app = builder.Build();
+        app.Run();
+
+        // Verify that Dockerfile was generated
+        var dockerfilePath = Path.Combine(outputDir.Path, "script-app.Dockerfile");
+        Assert.True(File.Exists(dockerfilePath), "Dockerfile should be generated for non-UV Python app");
+
+        var dockerfileContent = File.ReadAllText(dockerfilePath);
+
+        // Verify it's a fallback Dockerfile (single stage, no UV)
+        Assert.DoesNotContain("uv sync", dockerfileContent);
+        Assert.DoesNotContain("ghcr.io/astral-sh/uv", dockerfileContent);
+
+        // Verify it doesn't have pip install since there's no requirements.txt
+        Assert.DoesNotContain("pip install", dockerfileContent);
+
+        // Verify it uses the same runtime image as UV workflow
+        Assert.Contains("FROM python:3.11-slim-bookworm", dockerfileContent);
+
+        await Verify(dockerfileContent);
+    }
+
+    [Fact]
+    public async Task FallbackDockerfile_GeneratesDockerfileForAllEntrypointTypes()
+    {
+        using var sourceDir = new TempDirectory();
+        using var outputDir = new TempDirectory();
+        var projectDirectory = sourceDir.Path;
+
+        // Create a Python project without UV
+        var scriptContent = """
+            print("Hello!")
+            """;
+
+        var pythonVersionContent = "3.12";
+
+        File.WriteAllText(Path.Combine(projectDirectory, "main.py"), scriptContent);
+        File.WriteAllText(Path.Combine(projectDirectory, ".python-version"), pythonVersionContent);
+
+        using var builder = TestDistributedApplicationBuilder.Create(DistributedApplicationOperation.Publish, outputDir.Path, step: "publish-manifest");
+
+        // Add Python resources with different entrypoint types, none using UV
+        builder.AddPythonScript("script-app", projectDirectory, "main.py");
+        builder.AddPythonModule("module-app", projectDirectory, "mymodule");
+        builder.AddPythonExecutable("executable-app", projectDirectory, "pytest");
+
+        var app = builder.Build();
+        app.Run();
+
+        // Verify that Dockerfiles were generated for each entrypoint type
+        var scriptDockerfilePath = Path.Combine(outputDir.Path, "script-app.Dockerfile");
+        Assert.True(File.Exists(scriptDockerfilePath), "Dockerfile should be generated for script entrypoint");
+
+        var moduleDockerfilePath = Path.Combine(outputDir.Path, "module-app.Dockerfile");
+        Assert.True(File.Exists(moduleDockerfilePath), "Dockerfile should be generated for module entrypoint");
+
+        var executableDockerfilePath = Path.Combine(outputDir.Path, "executable-app.Dockerfile");
+        Assert.True(File.Exists(executableDockerfilePath), "Dockerfile should be generated for executable entrypoint");
+
+        var scriptDockerfileContent = File.ReadAllText(scriptDockerfilePath);
+        var moduleDockerfileContent = File.ReadAllText(moduleDockerfilePath);
+        var executableDockerfileContent = File.ReadAllText(executableDockerfilePath);
+
+        // Verify none use UV
+        Assert.DoesNotContain("uv sync", scriptDockerfileContent);
+        Assert.DoesNotContain("uv sync", moduleDockerfileContent);
+        Assert.DoesNotContain("uv sync", executableDockerfileContent);
+
+        // Verify correct entrypoints
+        Assert.Contains("ENTRYPOINT [\"python\",\"main.py\"]", scriptDockerfileContent);
+        Assert.Contains("ENTRYPOINT [\"python\",\"-m\",\"mymodule\"]", moduleDockerfileContent);
+        Assert.Contains("ENTRYPOINT [\"pytest\"]", executableDockerfileContent);
+
+        await Verify(scriptDockerfileContent)
+            .AppendContentAsFile(moduleDockerfileContent)
+            .AppendContentAsFile(executableDockerfileContent);
+    }
 }
 

tests/Aspire.Hosting.Python.Tests/AddPythonAppTests.cs

@@ -0,0 +1,23 @@
+FROM python:3.12-slim-bookworm
+
+# ------------------------------
+# 🚀 Python Application
+# ------------------------------
+# Create non-root user for security
+RUN groupadd --system --gid 999 appuser && useradd --system --gid 999 --uid 999 --create-home appuser
+
+# Set working directory
+WORKDIR /app
+
+# Copy application files
+COPY --chown=appuser:appuser . /app
+
+# Set environment variables
+ENV PYTHONDONTWRITEBYTECODE=1
+ENV PYTHONUNBUFFERED=1
+
+# Use the non-root user to run the application
+USER appuser
+
+# Run the application
+ENTRYPOINT ["python","main.py"]

tests/Aspire.Hosting.Python.Tests/Snapshots/AddPythonAppTests.FallbackDockerfile_GeneratesDockerfileForAllEntrypointTypes#00.verified.txt

@@ -0,0 +1,23 @@
+FROM python:3.12-slim-bookworm
+
+# ------------------------------
+# 🚀 Python Application
+# ------------------------------
+# Create non-root user for security
+RUN groupadd --system --gid 999 appuser && useradd --system --gid 999 --uid 999 --create-home appuser
+
+# Set working directory
+WORKDIR /app
+
+# Copy application files
+COPY --chown=appuser:appuser . /app
+
+# Set environment variables
+ENV PYTHONDONTWRITEBYTECODE=1
+ENV PYTHONUNBUFFERED=1
+
+# Use the non-root user to run the application
+USER appuser
+
+# Run the application
+ENTRYPOINT ["python","-m","mymodule"]

tests/Aspire.Hosting.Python.Tests/Snapshots/AddPythonAppTests.FallbackDockerfile_GeneratesDockerfileForAllEntrypointTypes#01.verified.txt

@@ -0,0 +1,23 @@
+FROM python:3.12-slim-bookworm
+
+# ------------------------------
+# 🚀 Python Application
+# ------------------------------
+# Create non-root user for security
+RUN groupadd --system --gid 999 appuser && useradd --system --gid 999 --uid 999 --create-home appuser
+
+# Set working directory
+WORKDIR /app
+
+# Copy application files
+COPY --chown=appuser:appuser . /app
+
+# Set environment variables
+ENV PYTHONDONTWRITEBYTECODE=1
+ENV PYTHONUNBUFFERED=1
+
+# Use the non-root user to run the application
+USER appuser
+
+# Run the application
+ENTRYPOINT ["pytest"]

tests/Aspire.Hosting.Python.Tests/Snapshots/AddPythonAppTests.FallbackDockerfile_GeneratesDockerfileForAllEntrypointTypes#02.verified.txt

@@ -0,0 +1,33 @@
+FROM python:3.13-slim-bookworm
+
+# ------------------------------
+# 🚀 Python Application
+# ------------------------------
+# Create non-root user for security
+RUN groupadd --system --gid 999 appuser && useradd --system --gid 999 --uid 999 --create-home appuser
+
+# Set working directory
+WORKDIR /app
+
+# Copy requirements.txt for dependency installation
+COPY requirements.txt /app/requirements.txt
+
+# Install dependencies using pip
+RUN apt-get update \
+  && apt-get install -y --no-install-recommends build-essential \
+  && pip install --no-cache-dir -r requirements.txt \
+  && apt-get purge -y --auto-remove build-essential \
+  && rm -rf /var/lib/apt/lists/*
+
+# Copy application files
+COPY --chown=appuser:appuser . /app
+
+# Set environment variables
+ENV PYTHONDONTWRITEBYTECODE=1
+ENV PYTHONUNBUFFERED=1
+
+# Use the non-root user to run the application
+USER appuser
+
+# Run the application
+ENTRYPOINT ["python","main.py"]

tests/Aspire.Hosting.Python.Tests/Snapshots/AddPythonAppTests.FallbackDockerfile_GeneratesDockerfileWithoutUv_WithRequirementsTxt.verified.txt

@@ -0,0 +1,23 @@
+FROM python:3.11-slim-bookworm
+
+# ------------------------------
+# 🚀 Python Application
+# ------------------------------
+# Create non-root user for security
+RUN groupadd --system --gid 999 appuser && useradd --system --gid 999 --uid 999 --create-home appuser
+
+# Set working directory
+WORKDIR /app
+
+# Copy application files
+COPY --chown=appuser:appuser . /app
+
+# Set environment variables
+ENV PYTHONDONTWRITEBYTECODE=1
+ENV PYTHONUNBUFFERED=1
+
+# Use the non-root user to run the application
+USER appuser
+
+# Run the application
+ENTRYPOINT ["python","main.py"]