Merge pull request #1 from imjasonh/feat/multi-arch-support

feat: Add multi-arch support

.cargo/config.toml

@@ -0,0 +1,5 @@
+[target.x86_64-unknown-linux-musl]
+linker = "x86_64-linux-musl-gcc"
+
+[target.aarch64-unknown-linux-musl]
+linker = "aarch64-linux-musl-gcc"

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest]
+        os: [ubuntu-latest, ubuntu-24.04-arm]
         rust: [stable, beta]
     steps:
     - uses: actions/checkout@v4
@@ -24,12 +24,11 @@ jobs:
       uses: dtolnay/rust-toolchain@master
       with:
         toolchain: ${{ matrix.rust }}
-        targets: x86_64-unknown-linux-musl
-    - name: Install cross-compilation tools (Ubuntu)
-      if: matrix.os == 'ubuntu-latest'
+        targets: x86_64-unknown-linux-musl,aarch64-unknown-linux-musl
+    - name: Install cross-compilation tools for both architectures
       run: |
         sudo apt-get update
-        sudo apt-get install -y musl-tools
+        sudo apt-get install -y musl-tools gcc-aarch64-linux-gnu gcc-x86-64-linux-gnu
     - name: Cache cargo registry
       uses: actions/cache@v4
       with:
@@ -45,6 +44,16 @@ jobs:
       with:
         path: target
         key: ${{ runner.os }}-cargo-build-target-${{ hashFiles('**/Cargo.lock') }}
+    - name: Setup cargo config for cross-compilation
+      run: |
+        mkdir -p .cargo
+        cat > .cargo/config.toml << 'EOF'
+        [target.x86_64-unknown-linux-musl]
+        linker = "x86_64-linux-musl-gcc"
+
+        [target.aarch64-unknown-linux-musl]
+        linker = "aarch64-linux-gnu-gcc"
+        EOF
     - name: Verify cross-compilation setup (Unix)
       run: |
         echo "Installed targets:"
@@ -57,9 +66,10 @@ jobs:
         which x86_64-unknown-linux-musl-gcc || echo "x86_64-unknown-linux-musl-gcc not found"
         which x86_64-linux-musl-gcc || echo "x86_64-linux-musl-gcc not found"
         which musl-gcc || echo "musl-gcc not found"
+        which aarch64-linux-gnu-gcc || echo "aarch64-linux-gnu-gcc not found"
         which rust-lld || echo "rust-lld not found"
         echo "Cargo config:"
-        cat ~/.cargo/config.toml || echo "No cargo config found"
+        cat .cargo/config.toml || echo "No cargo config found"
     - name: Build
       run: cargo build --verbose
     - name: Run unit tests
@@ -105,11 +115,21 @@ jobs:
     - name: Install Rust
       uses: dtolnay/rust-toolchain@stable
       with:
-        targets: x86_64-unknown-linux-musl
+        targets: x86_64-unknown-linux-musl,aarch64-unknown-linux-musl
     - name: Install musl tools
       run: |
         sudo apt-get update
-        sudo apt-get install -y musl-tools
+        sudo apt-get install -y musl-tools gcc-aarch64-linux-gnu
+    - name: Setup cargo config for cross-compilation
+      run: |
+        mkdir -p .cargo
+        cat > .cargo/config.toml << 'EOF'
+        [target.x86_64-unknown-linux-musl]
+        linker = "x86_64-linux-musl-gcc"
+
+        [target.aarch64-unknown-linux-musl]
+        linker = "aarch64-linux-gnu-gcc"
+        EOF
     - name: Set up Docker Buildx
       uses: docker/setup-buildx-action@v3
     - name: Build krust
@@ -136,6 +156,15 @@ jobs:
       run: |
         cd example/hello-krust
         krust build --no-push --image local.test/hello:latest ./
+    - name: Test multi-arch build and run
+      run: |
+        cd example/hello-krust
+        # Build for both platforms and push
+        export KRUST_REPO=ttl.sh/${{ github.run_id }}-multiarch
+        IMAGE_REF=$(krust build --platform linux/amd64,linux/arm64 ./)
+        echo "Built multi-arch image: $IMAGE_REF"
+        # Run the image - should automatically select the right architecture
+        docker run --rm $IMAGE_REF
 
   # Takes too long to run on CI, so it's commented out for now.
   # coverage:

Cargo.toml

@@ -25,6 +25,7 @@ tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 dirs = "5.0"
 toml = "0.8"
 which = "6.0"
+tempfile = "3.9"
 
 [dev-dependencies]
 tempfile = "3.9"

README.md

@@ -100,8 +100,17 @@ krust build example/hello-krust --no-push
 # Use a specific image name (overrides KRUST_REPO)
 krust build --image myregistry.io/myapp:v1.0
 
-# Build for a different platform
+# Build for a specific platform
 krust build --platform linux/arm64
+
+# Build for multiple platforms (multi-arch)
+krust build --platform linux/amd64,linux/arm64
+
+# Or specify platforms separately
+krust build --platform linux/amd64 --platform linux/arm64
+
+# Default behavior builds for both amd64 and arm64
+krust build
 ```
 
 ### Build with custom cargo arguments
@@ -116,6 +125,31 @@ krust build -- --features=prod
 - `linux/arm64` (aarch64-unknown-linux-musl)
 - `linux/arm/v7` (armv7-unknown-linux-musleabihf)
 
+### Multi-Architecture Images
+
+krust always pushes OCI image indexes (manifest lists) for consistency:
+1. Builds each platform separately with its own binary
+2. Pushes platform-specific images with unique tags
+3. Creates and pushes a manifest list that references all platforms
+4. Returns the manifest list digest for use with Docker/Kubernetes
+
+This means even single-platform builds result in a manifest list, ensuring a uniform interface regardless of the number of platforms built.
+
+## Build Process
+
+krust builds your Rust application in an isolated environment:
+
+1. **Temporary build directory** - Each build uses a unique temporary directory via `--target-dir`
+2. **Static compilation** - Builds with `RUSTFLAGS="-C target-feature=+crt-static"` for musl targets
+3. **Cross-compilation** - Automatically configures the appropriate linker for the target platform
+4. **Binary extraction** - Copies the built binary from the temp directory for packaging
+5. **Container creation** - Packages the binary into a minimal OCI image
+
+This approach ensures:
+- No conflicts between concurrent builds
+- Clean builds without interference from previous compilations
+- Safe parallel execution of multiple krust instances
+
 ## Static Binaries
 
 krust builds fully static binaries by default using:
@@ -185,9 +219,12 @@ When determining the base image, krust uses this precedence order:
 - **Docker-free** - Builds OCI container images without requiring Docker daemon
 - **Static binaries** - Produces truly static binaries using musl libc
 - **Composable** - Outputs image digest to stdout, enabling `docker run $(krust build)`
+- **Multi-arch support** - Build for multiple platforms in a single command
 - **Cross-platform** - Supports multiple architectures (amd64, arm64, arm/v7)
 - **Minimal images** - Uses distroless base images for security and size
 - **OCI compliant** - Works with any OCI-compliant container registry
+- **Isolated builds** - Each build uses a temporary directory to avoid conflicts
+- **Concurrent builds** - Multiple builds can run safely in parallel
 
 ## Example
 
@@ -260,6 +297,15 @@ This is normal when building linux/amd64 images on Apple Silicon. The images wil
 git clone https://github.com/imjasonh/krust.git
 cd krust
 
+# Install cross-compilation toolchain (required for tests)
+# On macOS:
+brew install messense/macos-cross-toolchains/x86_64-unknown-linux-musl
+brew install messense/macos-cross-toolchains/aarch64-unknown-linux-musl
+
+# Install Rust targets
+rustup target add x86_64-unknown-linux-musl
+rustup target add aarch64-unknown-linux-musl  # Optional, for ARM64 support
+
 # Install pre-commit hooks
 pip install pre-commit
   or

src/builder/mod.rs

@@ -1,6 +1,7 @@
 use anyhow::{Context, Result};
 use std::path::{Path, PathBuf};
 use std::process::Command;
+use tempfile::TempDir;
 use tracing::{debug, error, info};
 
 #[cfg(test)]
@@ -12,6 +13,11 @@ pub struct RustBuilder {
     cargo_args: Vec<String>,
 }
 
+pub struct BuildResult {
+    pub binary_path: PathBuf,
+    _temp_dir: TempDir, // Keep temp dir alive until BuildResult is dropped
+}
+
 impl RustBuilder {
     pub fn new(project_path: impl AsRef<Path>, target: &str) -> Self {
         Self {
@@ -26,14 +32,21 @@ impl RustBuilder {
         self
     }
 
-    pub fn build(&self) -> Result<PathBuf> {
+    pub fn build(&self) -> Result<BuildResult> {
         info!("Building Rust project at {:?}", self.project_path);
 
+        // Use a unique target directory to avoid conflicts between concurrent builds
+        let temp_target_dir =
+            tempfile::tempdir().context("Failed to create temporary directory")?;
+        let target_dir = temp_target_dir.path();
+
         let mut cmd = Command::new("cargo");
         cmd.arg("build")
             .arg("--release")
             .arg("--target")
             .arg(&self.target)
+            .arg("--target-dir")
+            .arg(target_dir)
             .current_dir(&self.project_path);
 
         // Set RUSTFLAGS for static linking
@@ -116,6 +129,7 @@ impl RustBuilder {
         debug!("Running command: {:?}", cmd);
         debug!("RUSTFLAGS: {}", rustflags);
 
+        info!("Running cargo build for target: {}", self.target);
         let output = cmd.output().context("Failed to execute cargo build")?;
 
         if !output.status.success() {
@@ -128,19 +142,30 @@ impl RustBuilder {
         }
 
         let binary_name = self.get_binary_name()?;
-        let binary_path = self
-            .project_path
-            .join("target")
+        let binary_path = target_dir
             .join(&self.target)
             .join("release")
             .join(&binary_name);
 
+        // Sometimes cargo build completes but the binary isn't immediately visible
+        // due to filesystem sync issues. Give it a moment.
+        let mut retries = 0;
+        while !binary_path.exists() && retries < 3 {
+            std::thread::sleep(std::time::Duration::from_millis(100));
+            retries += 1;
+        }
+
         if !binary_path.exists() {
             anyhow::bail!("Built binary not found at {:?}", binary_path);
         }
 
         info!("Successfully built binary at {:?}", binary_path);
-        Ok(binary_path)
+
+        // Return the build result with the temp directory to keep it alive
+        Ok(BuildResult {
+            binary_path,
+            _temp_dir: temp_target_dir,
+        })
     }
 
     fn get_binary_name(&self) -> Result<String> {

src/cli/mod.rs

@@ -25,9 +25,10 @@ pub enum Commands {
         #[arg(short, long, env = "KRUST_IMAGE")]
         image: Option<String>,
 
-        /// Target platform (e.g., linux/amd64, linux/arm64)
-        #[arg(long, default_value = "linux/amd64")]
-        platform: String,
+        /// Target platforms (e.g., linux/amd64, linux/arm64)
+        /// Can be specified multiple times or as a comma-separated list
+        #[arg(long, value_delimiter = ',')]
+        platform: Option<Vec<String>>,
 
         /// Skip pushing the image to the registry after building
         #[arg(long)]

src/lib.rs

@@ -2,6 +2,7 @@ pub mod builder;
 pub mod cli;
 pub mod config;
 pub mod image;
+pub mod manifest;
 pub mod registry;
 
 pub use anyhow::Result;

src/main.rs

@@ -5,6 +5,7 @@ use krust::{
     cli::{Cli, Commands},
     config::Config,
     image::ImageBuilder,
+    manifest::{ManifestDescriptor, Platform},
     registry::RegistryClient,
 };
 use std::path::{Path, PathBuf};
@@ -57,33 +58,109 @@ async fn main() -> Result<()> {
                 format!("{}/{}:latest", repo, project_name)
             };
 
-            // Build the Rust binary
-            let target = get_rust_target_triple(&platform)?;
-            let builder = RustBuilder::new(&project_path, &target).with_cargo_args(cargo_args);
+            // Determine platforms to build for
+            let platforms = if let Some(platforms) = platform {
+                platforms
+            } else {
+                // Default to common platforms
+                vec!["linux/amd64".to_string(), "linux/arm64".to_string()]
+            };
 
-            let binary_path = builder.build()?;
+            // Build for each platform
+            let mut manifest_descriptors = Vec::new();
+            let auth = oci_distribution::secrets::RegistryAuth::Anonymous;
+            let mut registry_client = RegistryClient::new(auth)?;
 
-            // Build container image
-            let image_builder = ImageBuilder::new(binary_path, base_image, platform.clone());
+            for platform_str in &platforms {
+                info!("Building for platform: {}", platform_str);
 
-            let (config_data, layer_data, manifest) = image_builder.build()?;
+                // Build the Rust binary for this platform
+                let target = get_rust_target_triple(platform_str)?;
+                let builder =
+                    RustBuilder::new(&project_path, &target).with_cargo_args(cargo_args.clone());
 
-            // Push by default unless --no-push is specified
+                let build_result = builder.build()?;
+
+                // Build container image for this platform
+                let image_builder = ImageBuilder::new(
+                    build_result.binary_path,
+                    base_image.clone(),
+                    platform_str.clone(),
+                );
+
+                let (config_data, layer_data, manifest) = image_builder.build()?;
+
+                // Push platform-specific image if not --no-push
+                if !no_push {
+                    info!("Pushing image for platform: {}", platform_str);
+
+                    let layers = vec![(layer_data, manifest.layers[0].media_type.clone())];
+
+                    // For manifest lists to work properly, we need to push to a consistent location
+                    // We'll use the base image ref with a unique tag for each platform
+                    let (base_ref, _) = if let Some(pos) = image_ref.rfind(':') {
+                        (
+                            image_ref[..pos].to_string(),
+                            image_ref[pos + 1..].to_string(),
+                        )
+                    } else {
+                        (image_ref.to_string(), "latest".to_string())
+                    };
+
+                    // Create a unique tag for this platform to avoid conflicts
+                    let platform_tag = format!("platform-{}", platform_str.replace('/', "-"));
+                    let platform_ref = format!("{}:{}", base_ref, platform_tag);
+
+                    let (digest_ref, manifest_size) = registry_client
+                        .push_image(&platform_ref, config_data, layers)
+                        .await?;
+
+                    // Parse platform string
+                    let parts: Vec<&str> = platform_str.split('/').collect();
+                    let (os, arch) = if parts.len() >= 2 {
+                        (parts[0].to_string(), parts[1].to_string())
+                    } else {
+                        return Err(anyhow::anyhow!("Invalid platform format: {}", platform_str));
+                    };
+
+                    // Extract just the digest from the full reference
+                    let digest = digest_ref.split('@').next_back().unwrap_or("").to_string();
+
+                    info!("Pushed platform image to: {}", digest_ref);
+
+                    // Add to manifest list
+                    info!(
+                        "Adding manifest to list - platform: {}/{}, digest: {}, size: {}",
+                        os, arch, digest, manifest_size
+                    );
+                    manifest_descriptors.push(ManifestDescriptor {
+                        media_type: "application/vnd.oci.image.manifest.v1+json".to_string(),
+                        size: manifest_size as i64,
+                        digest,
+                        platform: Platform {
+                            architecture: arch,
+                            os,
+                            variant: None,
+                        },
+                    });
+                }
+            }
+
+            // Always push manifest list if not --no-push (even for single platform)
             if !no_push {
-                info!("Pushing image to registry...");
-                let auth = oci_distribution::secrets::RegistryAuth::Anonymous;
-                let mut registry_client = RegistryClient::new(auth)?;
+                info!("Creating and pushing manifest list...");
 
-                let layers = vec![(layer_data, manifest.layers[0].media_type.clone())];
-
-                let digest_ref = registry_client
-                    .push_image(&image_ref, config_data, layers)
+                let manifest_list_ref = registry_client
+                    .push_manifest_list(&image_ref, manifest_descriptors)
                     .await?;
 
-                // Print only the digest reference to stdout
-                println!("{}", digest_ref);
+                // Output the manifest list reference
+                println!("{}", manifest_list_ref);
             } else {
-                info!("Successfully built image: {}", image_ref);
+                info!(
+                    "Successfully built image for {} platform(s)",
+                    platforms.len()
+                );
                 info!("Skipping push (--no-push specified)");
             }
         }

src/manifest.rs

@@ -0,0 +1,40 @@
+use serde::{Deserialize, Serialize};
+
+/// OCI Image Index (manifest list) for multi-arch support
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ImageIndex {
+    #[serde(rename = "schemaVersion")]
+    pub schema_version: i32,
+    #[serde(rename = "mediaType")]
+    pub media_type: String,
+    pub manifests: Vec<ManifestDescriptor>,
+}
+
+/// Descriptor for a platform-specific manifest in the index
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ManifestDescriptor {
+    #[serde(rename = "mediaType")]
+    pub media_type: String,
+    pub size: i64,
+    pub digest: String,
+    pub platform: Platform,
+}
+
+/// Platform information for a manifest
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Platform {
+    pub architecture: String,
+    pub os: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub variant: Option<String>,
+}
+
+impl ImageIndex {
+    pub fn new(manifests: Vec<ManifestDescriptor>) -> Self {
+        Self {
+            schema_version: 2,
+            media_type: "application/vnd.oci.image.index.v1+json".to_string(),
+            manifests,
+        }
+    }
+}

src/registry/mod.rs

@@ -2,6 +2,7 @@ use anyhow::{Context, Result};
 use oci_distribution::manifest::{OciDescriptor, OciImageManifest, OciManifest};
 use oci_distribution::secrets::RegistryAuth;
 use oci_distribution::{Client, Reference};
+use std::str::FromStr;
 use tracing::{debug, info};
 
 #[cfg(test)]
@@ -24,7 +25,7 @@ impl RegistryClient {
         image_ref: &str,
         config_data: Vec<u8>,
         layers: Vec<(Vec<u8>, String)>,
-    ) -> Result<String> {
+    ) -> Result<(String, usize)> {
         let reference: Reference = image_ref
             .parse()
             .context("Failed to parse image reference")?;
@@ -100,7 +101,82 @@ impl RegistryClient {
         let repository = reference.repository();
         let digest_ref = format!("{}/{}@{}", registry, repository, digest);
 
-        Ok(digest_ref)
+        // Return both the digest ref and the actual manifest size
+        let manifest_size = serde_json::to_vec(&manifest)?.len();
+        Ok((digest_ref, manifest_size))
+    }
+
+    pub async fn push_manifest_list(
+        &mut self,
+        image_ref: &str,
+        manifest_descriptors: Vec<crate::manifest::ManifestDescriptor>,
+    ) -> Result<String> {
+        let reference = Reference::from_str(image_ref)
+            .context(format!("Failed to parse image reference: {}", image_ref))?;
+
+        // Create the image index
+        let index = crate::manifest::ImageIndex::new(manifest_descriptors);
+
+        // Convert to OCI index
+        let oci_manifests: Vec<oci_distribution::manifest::ImageIndexEntry> = index
+            .manifests
+            .iter()
+            .map(|m| oci_distribution::manifest::ImageIndexEntry {
+                media_type: m.media_type.clone(),
+                digest: m.digest.clone(),
+                size: m.size,
+                platform: Some(oci_distribution::manifest::Platform {
+                    architecture: m.platform.architecture.clone(),
+                    os: m.platform.os.clone(),
+                    os_version: None,
+                    os_features: None,
+                    variant: m.platform.variant.clone(),
+                    features: None,
+                }),
+                annotations: None,
+            })
+            .collect();
+
+        let oci_index = oci_distribution::manifest::OciImageIndex {
+            schema_version: 2,
+            media_type: Some("application/vnd.oci.image.index.v1+json".to_string()),
+            manifests: oci_manifests,
+            annotations: None,
+        };
+
+        // Wrap in OciManifest enum
+        let manifest = oci_distribution::manifest::OciManifest::ImageIndex(oci_index);
+
+        debug!(
+            "Pushing manifest list with {} manifests",
+            index.manifests.len()
+        );
+        for m in &index.manifests {
+            debug!(
+                "  - Platform: {}/{}, digest: {}",
+                m.platform.os, m.platform.architecture, m.digest
+            );
+        }
+        let manifest_url = self
+            .client
+            .push_manifest(&reference, &manifest)
+            .await
+            .context("Failed to push manifest list")?;
+
+        info!("Successfully pushed manifest list to {}", manifest_url);
+
+        // Extract digest from the manifest URL
+        let digest = manifest_url
+            .split('/')
+            .next_back()
+            .context("Failed to extract digest from manifest URL")?;
+
+        // Build the full image reference with digest
+        let registry = reference.registry();
+        let repository = reference.repository();
+        let image_ref = format!("{}/{}@{}", registry, repository, digest);
+
+        Ok(image_ref)
     }
 }
 

tests/integration_test.rs

@@ -4,6 +4,23 @@ use predicates::prelude::*;
 use std::env;
 use std::process::Command as StdCommand;
 
+// Helper to get the appropriate test platform based on runtime architecture
+fn get_test_platform() -> &'static str {
+    // In CI, test the native platform
+    if env::var("CI").is_ok() {
+        if cfg!(target_arch = "x86_64") {
+            "linux/amd64"
+        } else if cfg!(target_arch = "aarch64") {
+            "linux/arm64"
+        } else {
+            "linux/amd64"
+        }
+    } else {
+        // For local development, always use amd64 as it's most commonly available
+        "linux/amd64"
+    }
+}
+
 #[test]
 fn test_version_command() -> Result<()> {
     let mut cmd = Command::cargo_bin("krust")?;
@@ -72,6 +89,8 @@ fn test_build_with_krust_repo_env() -> Result<()> {
     let mut cmd = Command::cargo_bin("krust")?;
     cmd.arg("build")
         .arg("--no-push")
+        .arg("--platform")
+        .arg(get_test_platform())
         .arg(".") // Explicitly pass current directory
         .env("KRUST_REPO", "test.local")
         .current_dir(&example_dir);
@@ -80,7 +99,7 @@ fn test_build_with_krust_repo_env() -> Result<()> {
         .success()
         .stderr(predicate::str::contains("Building Rust project"))
         .stderr(predicate::str::contains(
-            "Successfully built image: test.local/hello-krust:latest",
+            "Successfully built image for 1 platform(s)",
         ));
     Ok(())
 }
@@ -95,6 +114,8 @@ fn test_command_substitution_syntax() -> Result<()> {
     let output = cmd
         .arg("build")
         .arg("--no-push")
+        .arg("--platform")
+        .arg(get_test_platform())
         .arg("--image")
         .arg("test.local/hello:latest")
         .arg(".") // Explicitly pass current directory
@@ -123,6 +144,8 @@ fn test_verbose_logging() -> Result<()> {
     cmd.arg("--verbose")
         .arg("build")
         .arg("--no-push")
+        .arg("--platform")
+        .arg(get_test_platform())
         .arg("--image")
         .arg("test.local/hello:latest")
         .arg(".") // Explicitly pass current directory
@@ -152,15 +175,27 @@ fn test_full_build_and_run_workflow() -> Result<()> {
     let example_dir = env::current_dir()?.join("example").join("hello-krust");
 
     // Build and push to ttl.sh
+    // For the full workflow test, build for the actual native platform so Docker can run it
+    let native_platform = if cfg!(target_arch = "aarch64") {
+        "linux/arm64"
+    } else {
+        "linux/amd64"
+    };
+
     let mut cmd = Command::cargo_bin("krust")?;
     let output = cmd
         .arg("build")
+        .arg("--platform")
+        .arg(native_platform)
         .arg(".") // Explicitly pass current directory
         .env("KRUST_REPO", "ttl.sh/krust-test")
         .current_dir(&example_dir)
         .output()?;
 
-    assert!(output.status.success(), "Build failed");
+    if !output.status.success() {
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        panic!("Build failed: {}", stderr);
+    }
 
     // Get the image reference from stdout
     let image_ref = String::from_utf8_lossy(&output.stdout).trim().to_string();
@@ -171,8 +206,136 @@ fn test_full_build_and_run_workflow() -> Result<()> {
         .args(&["run", "--rm", &image_ref])
         .output()?;
 
-    assert!(docker_output.status.success(), "Docker run failed");
+    if !docker_output.status.success() {
+        let stderr = String::from_utf8_lossy(&docker_output.stderr);
+        panic!("Docker run failed with image {}: {}", image_ref, stderr);
+    }
+
     let docker_stdout = String::from_utf8_lossy(&docker_output.stdout);
     assert!(docker_stdout.contains("Hello from krust example!"));
     Ok(())
 }
+
+#[test]
+fn test_single_platform_build() -> Result<()> {
+    let example_dir = env::current_dir()?.join("example").join("hello-krust");
+    let platform = get_test_platform();
+
+    let mut cmd = Command::cargo_bin("krust")?;
+    cmd.arg("build")
+        .arg("--no-push")
+        .arg("--platform")
+        .arg(platform)
+        .arg("--image")
+        .arg("test.local/single-platform:latest")
+        .arg(".")
+        .current_dir(&example_dir);
+
+    cmd.assert()
+        .success()
+        .stderr(predicate::str::contains(format!(
+            "Building for platform: {}",
+            platform
+        )))
+        .stderr(predicate::str::contains(
+            "Successfully built image for 1 platform(s)",
+        ));
+    Ok(())
+}
+
+#[test]
+fn test_multi_platform_build() -> Result<()> {
+    let example_dir = env::current_dir()?.join("example").join("hello-krust");
+    let mut cmd = Command::cargo_bin("krust")?;
+
+    // Test building for multiple platforms
+    // This will use whatever targets are available
+    cmd.arg("build")
+        .arg("--no-push")
+        .arg("--platform")
+        .arg("linux/amd64,linux/arm64")
+        .arg("--image")
+        .arg("test.local/multi-platform:latest")
+        .arg(".")
+        .current_dir(&example_dir);
+
+    // The command might fail if targets aren't installed, but we should test that it tries
+    let output = cmd.output()?;
+
+    if output.status.success() {
+        // If it succeeds, verify we built for multiple platforms
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        assert!(stderr.contains("Building for platform: linux/amd64"));
+        assert!(stderr.contains("Building for platform: linux/arm64"));
+        assert!(stderr.contains("Successfully built image for 2 platform(s)"));
+    } else {
+        // If it fails, it should be because of missing targets
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        assert!(
+            stderr.contains("target may not be installed")
+                || stderr.contains("linker")
+                || stderr.contains("cross-compilation")
+                || stderr.contains("not found"),
+            "Build failed for unexpected reason: {}",
+            stderr
+        );
+    }
+    Ok(())
+}
+
+#[test]
+fn test_multi_arch_build_and_run() -> Result<()> {
+    // This test requires Docker
+    let docker_check = StdCommand::new("docker").arg("version").output();
+    match docker_check {
+        Ok(output) if output.status.success() => {
+            // Docker is available, proceed with test
+        }
+        _ => {
+            eprintln!("Docker is required for this test but is not available");
+            return Ok(());
+        }
+    }
+
+    let example_dir = env::current_dir()?.join("example").join("hello-krust");
+
+    // Build multi-arch image and push to ttl.sh
+    let mut cmd = Command::cargo_bin("krust")?;
+    let output = cmd
+        .arg("build")
+        .arg("--platform")
+        .arg("linux/amd64,linux/arm64")
+        .arg(".")
+        .env("KRUST_REPO", "ttl.sh/krust-multiarch-test")
+        .current_dir(&example_dir)
+        .output()?;
+
+    if !output.status.success() {
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        // If it fails due to missing targets, that's expected in some environments
+        if stderr.contains("target may not be installed")
+            || stderr.contains("linker")
+            || stderr.contains("cross-compilation")
+            || stderr.contains("not found")
+        {
+            eprintln!("Skipping multi-arch run test - build failed due to missing toolchain");
+            return Ok(());
+        }
+        panic!("Build failed unexpectedly: {}", stderr);
+    }
+
+    // Get the image reference from stdout
+    let image_ref = String::from_utf8_lossy(&output.stdout).trim().to_string();
+    assert!(image_ref.starts_with("ttl.sh/krust-multiarch-test/hello-krust"));
+
+    // Try to run the image - it should work on the current architecture
+    let docker_output = StdCommand::new("docker")
+        .args(&["run", "--rm", &image_ref])
+        .output()?;
+
+    assert!(docker_output.status.success(), "Docker run failed");
+    let docker_stdout = String::from_utf8_lossy(&docker_output.stdout);
+    assert!(docker_stdout.contains("Hello from krust example!"));
+
+    Ok(())
+}