Fix .env files being overwritten by Docker Compose publisher

src/Aspire.Hosting.Docker/DockerComposeEnvironmentResource.cs

@@ -50,8 +50,6 @@ public class DockerComposeEnvironmentResource : Resource, IComputeEnvironmentRes
 
     internal Dictionary<IResource, DockerComposeServiceResource> ResourceMapping { get; } = new(new ResourceNameComparer());
 
-    internal EnvFile? SharedEnvFile { get; set; }
-
     internal PortAllocator PortAllocator { get; } = new();
 
     /// <param name="name">The name of the Docker Compose environment.</param>
@@ -327,11 +325,14 @@ private async Task PrepareAsync(PipelineStepContext context)
     {
         var envFilePath = GetEnvFilePath(context);
 
-        if (CapturedEnvironmentVariables.Count == 0 || SharedEnvFile is null)
+        if (CapturedEnvironmentVariables.Count == 0)
         {
             return;
         }
 
+        // Initialize a new EnvFile for this environment
+        var envFile = EnvFile.Create(envFilePath, context.Logger);
+
         foreach (var entry in CapturedEnvironmentVariables)
         {
             var (key, (description, defaultValue, source)) = entry;
@@ -346,10 +347,10 @@ private async Task PrepareAsync(PipelineStepContext context)
                 defaultValue = imageName;
             }
 
-            SharedEnvFile.Add(key, defaultValue, description, onlyIfMissing: false);
+            envFile.Add(key, defaultValue, description, onlyIfMissing: false);
         }
 
-        SharedEnvFile.Save(envFilePath, includeValues: true);
+        envFile.Save(includeValues: true);
     }
 
     internal string AddEnvironmentVariable(string name, string? description = null, string? defaultValue = null, object? source = null)

src/Aspire.Hosting.Docker/DockerComposePublishingContext.cs

@@ -153,7 +153,7 @@ private async Task WriteDockerComposeOutputAsync(DistributedApplicationModel mod
             if (environment.CapturedEnvironmentVariables.Count > 0)
             {
                 var envFilePath = Path.Combine(OutputPath, ".env");
-                var envFile = environment.SharedEnvFile ?? EnvFile.Load(envFilePath);
+                var envFile = EnvFile.Load(envFilePath, logger);
 
                 foreach (var entry in environment.CapturedEnvironmentVariables ?? [])
                 {
@@ -162,9 +162,7 @@ private async Task WriteDockerComposeOutputAsync(DistributedApplicationModel mod
                     envFile.Add(key, value: null, description, onlyIfMissing: true);
                 }
 
-                environment.SharedEnvFile = envFile;
-
-                envFile.Save(envFilePath, includeValues: false);
+                envFile.Save(includeValues: false);
             }
 
             await writeTask.SucceedAsync(

src/Aspire.Hosting.Docker/EnvFile.cs

@@ -1,17 +1,32 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using Microsoft.Extensions.Logging;
+
 namespace Aspire.Hosting.Docker;
 
 internal sealed record EnvEntry(string Key, string? Value, string? Comment);
 
 internal sealed class EnvFile
 {
-    private readonly SortedDictionary<string, EnvEntry> _entries = [];
+    private string? _path;
+    private readonly ILogger? _logger;
+
+    internal SortedDictionary<string, EnvEntry> Entries { get; } = [];
+
+    private EnvFile(ILogger? logger = null)
+    {
+        _logger = logger;
+    }
+
+    public static EnvFile Create(string path, ILogger? logger = null)
+    {
+        return new EnvFile(logger) { _path = path };
+    }
 
-    public static EnvFile Load(string path)
+    public static EnvFile Load(string path, ILogger? logger = null)
     {
-        var envFile = new EnvFile();
+        var envFile = new EnvFile(logger) { _path = path };
         if (!File.Exists(path))
         {
             return envFile;
@@ -29,7 +44,7 @@ public static EnvFile Load(string path)
             }
             else if (TryParseKeyValue(line, out var key, out var value))
             {
-                envFile._entries[key] = new EnvEntry(key, value, currentComment);
+                envFile.Entries[key] = new EnvEntry(key, value, currentComment);
                 currentComment = null; // Reset comment after associating it with a key
             }
             else
@@ -43,12 +58,12 @@ public static EnvFile Load(string path)
 
     public void Add(string key, string? value, string? comment, bool onlyIfMissing = true)
     {
-        if (_entries.ContainsKey(key) && onlyIfMissing)
+        if (Entries.ContainsKey(key) && onlyIfMissing)
         {
             return;
         }
 
-        _entries[key] = new EnvEntry(key, value, comment);
+        Entries[key] = new EnvEntry(key, value, comment);
     }
 
     private static bool TryParseKeyValue(string line, out string key, out string? value)
@@ -69,11 +84,22 @@ private static bool TryParseKeyValue(string line, out string key, out string? va
         return false;
     }
 
-    public void Save(string path)
+    public void Save()
     {
+        if (_path is null)
+        {
+            throw new InvalidOperationException("Cannot save EnvFile without a path. Use Load() to create an EnvFile with a path.");
+        }
+
+        // Log if we're about to overwrite an existing file
+        if (File.Exists(_path))
+        {
+            _logger?.LogInformation("Environment file '{EnvFilePath}' already exists and will be overwritten", _path);
+        }
+
         var lines = new List<string>();
 
-        foreach (var entry in _entries.Values)
+        foreach (var entry in Entries.Values)
         {
             if (!string.IsNullOrWhiteSpace(entry.Comment))
             {
@@ -83,35 +109,51 @@ public void Save(string path)
             lines.Add(string.Empty);
         }
 
-        File.WriteAllLines(path, lines);
+        File.WriteAllLines(_path, lines);
     }
 
-    public void Save(string path, bool includeValues)
+    public void Save(bool includeValues)
     {
         if (includeValues)
         {
-            Save(path);
+            Save();
         }
         else
         {
-            SaveKeysOnly(path);
+            SaveKeysOnly();
         }
     }
 
-    private void SaveKeysOnly(string path)
+    private void SaveKeysOnly()
     {
+        if (_path is null)
+        {
+            throw new InvalidOperationException("Cannot save EnvFile without a path. Use Load() to create an EnvFile with a path.");
+        }
+
         var lines = new List<string>();
 
-        foreach (var entry in _entries.Values)
+        foreach (var entry in Entries.Values)
         {
             if (!string.IsNullOrWhiteSpace(entry.Comment))
             {
                 lines.Add($"# {entry.Comment}");
             }
-            lines.Add($"{entry.Key}=");
+
+            // If the entry already has a non-empty value (loaded from disk), preserve it
+            // This ensures user-modified values are not overwritten when we save keys only
+            if (!string.IsNullOrEmpty(entry.Value))
+            {
+                lines.Add($"{entry.Key}={entry.Value}");
+            }
+            else
+            {
+                lines.Add($"{entry.Key}=");
+            }
+
             lines.Add(string.Empty);
         }
 
-        File.WriteAllLines(path, lines);
+        File.WriteAllLines(_path, lines);
     }
 }

tests/Aspire.Hosting.Docker.Tests/DockerComposePublisherTests.cs

@@ -588,6 +588,69 @@ await Verify(envFileContent, "env")
             .UseParameters("various-parameters");
     }
 
+    [Fact]
+    public void PrepareStep_OverwritesExistingEnvFileAndLogsWarning()
+    {
+        using var tempDir = new TempDirectory();
+
+        var builder = TestDistributedApplicationBuilder.Create(DistributedApplicationOperation.Publish, tempDir.Path, step: "prepare-docker-compose");
+        builder.Services.AddSingleton<IResourceContainerImageBuilder, MockImageBuilder>();
+        builder.WithTestAndResourceLogging(outputHelper);
+
+        var environment = builder.AddDockerComposeEnvironment("docker-compose");
+
+        var param1 = builder.AddParameter("param1", "defaultValue1");
+
+        builder.AddContainer("testapp", "testimage")
+            .WithEnvironment("PARAM1", param1);
+
+        // Pre-create the env file to simulate it already existing
+        var envFilePath = Path.Combine(tempDir.Path, ".env.Production");
+        File.WriteAllText(envFilePath, "# Old content\nOLD_KEY=old_value\n");
+
+        var app = builder.Build();
+        app.Run();
+
+        // Verify the file was overwritten with new content
+        var envFileContent = File.ReadAllText(envFilePath);
+        Assert.Contains("PARAM1", envFileContent);
+        Assert.DoesNotContain("OLD_KEY", envFileContent);
+
+        // The log message should be captured by the test output helper
+        // We can verify it was called by checking the test output
+        // The xunit logger will output to outputHelper
+    }
+
+    [Fact]
+    public void PrepareStep_OverwritesExistingEnvFileWithCustomEnvironmentName()
+    {
+        using var tempDir = new TempDirectory();
+
+        var builder = TestDistributedApplicationBuilder.Create(DistributedApplicationOperation.Publish, tempDir.Path, step: "prepare-docker-compose");
+        builder.Services.AddSingleton<IResourceContainerImageBuilder, MockImageBuilder>();
+        builder.Services.AddSingleton<Microsoft.Extensions.Hosting.IHostEnvironment>(new TestHostEnvironment("Staging"));
+        builder.WithTestAndResourceLogging(outputHelper);
+
+        var environment = builder.AddDockerComposeEnvironment("docker-compose");
+
+        var param1 = builder.AddParameter("param1", "stagingValue");
+
+        builder.AddContainer("testapp", "testimage")
+            .WithEnvironment("PARAM1", param1);
+
+        // Pre-create the env file with custom environment name
+        var envFilePath = Path.Combine(tempDir.Path, ".env.Staging");
+        File.WriteAllText(envFilePath, "# Old staging content\nOLD_STAGING_KEY=old_staging_value\n");
+
+        var app = builder.Build();
+        app.Run();
+
+        // Verify the file was overwritten with new content
+        var envFileContent = File.ReadAllText(envFilePath);
+        Assert.Contains("PARAM1", envFileContent);
+        Assert.DoesNotContain("OLD_STAGING_KEY", envFileContent);
+    }
+
     private sealed class MockImageBuilder : IResourceContainerImageBuilder
     {
         public bool BuildImageCalled { get; private set; }

tests/Aspire.Hosting.Docker.Tests/EnvFileTests.cs

@@ -21,7 +21,7 @@ public void Add_WithOnlyIfMissingTrue_DoesNotAddDuplicate()
         // Load and try to add the same key with onlyIfMissing=true
         var envFile = EnvFile.Load(envFilePath);
         envFile.Add("KEY1", "value2", "New comment", onlyIfMissing: true);
-        envFile.Save(envFilePath);
+        envFile.Save();
 
         var lines = File.ReadAllLines(envFilePath);
         var keyLines = lines.Where(l => l.StartsWith("KEY1=")).ToArray();
@@ -47,7 +47,7 @@ public void Add_WithOnlyIfMissingFalse_UpdatesExistingKey()
         // Load and try to add the same key with onlyIfMissing=false
         var envFile = EnvFile.Load(envFilePath);
         envFile.Add("KEY1", "value2", "New comment", onlyIfMissing: false);
-        envFile.Save(envFilePath);
+        envFile.Save();
 
         var lines = File.ReadAllLines(envFilePath);
         var keyLines = lines.Where(l => l.StartsWith("KEY1=")).ToArray();
@@ -82,7 +82,7 @@ public void Add_WithOnlyIfMissingFalse_UpdatesImageNameWithoutDuplication()
         // Add IMAGE with onlyIfMissing=false (should update the existing value)
         envFile.Add("PROJECT1_IMAGE", "project1:1.0.0", "Container image name for project1", onlyIfMissing: false);
 
-        envFile.Save(envFilePath);
+        envFile.Save();
 
         var lines = File.ReadAllLines(envFilePath);
         var imageLines = lines.Where(l => l.StartsWith("PROJECT1_IMAGE=")).ToArray();
@@ -113,7 +113,7 @@ public void Add_NewKey_AddsToFile()
         // Load and add a new key
         var envFile = EnvFile.Load(envFilePath);
         envFile.Add("KEY2", "value2", "Comment for KEY2", onlyIfMissing: true);
-        envFile.Save(envFilePath);
+        envFile.Save();
 
         var lines = File.ReadAllLines(envFilePath);
 
@@ -133,7 +133,7 @@ public void Load_EmptyFile_ReturnsEmptyEnvFile()
 
         var envFile = EnvFile.Load(envFilePath);
         envFile.Add("KEY1", "value1", "Comment");
-        envFile.Save(envFilePath);
+        envFile.Save();
 
         var lines = File.ReadAllLines(envFilePath);
         Assert.Contains("KEY1=value1", lines);
@@ -148,7 +148,7 @@ public void Load_NonExistentFile_ReturnsEmptyEnvFile()
         // Don't create the file
         var envFile = EnvFile.Load(envFilePath);
         envFile.Add("KEY1", "value1", "Comment");
-        envFile.Save(envFilePath);
+        envFile.Save();
 
         Assert.True(File.Exists(envFilePath));
         var lines = File.ReadAllLines(envFilePath);

tests/Aspire.Hosting.Docker.Tests/Snapshots/DockerComposePublisherTests.DockerComposeAppendsNewKeysToEnvFileOnPublish#01.verified.env

@@ -1,5 +1,5 @@
 # Parameter param1
-PARAM1=
+PARAM1=changed
 
 # Parameter param2
 PARAM2=

tests/Aspire.Hosting.Docker.Tests/Snapshots/DockerComposePublisherTests.DockerComposeDoesNotOverwriteEnvFileOnPublish#01.verified.env

@@ -1,3 +1,3 @@
 # Parameter param1
-PARAM1=
+PARAM1=changed