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name: axum-service-architecture description: Service architecture patterns for Axum applications including layered design (Router → Handler → Service → Repository), AppState with FromRef for dependency injection, Tower ServiceBuilder for middleware composition, and modular router organization. Use when designing service layers, managing dependencies, composing middleware stacks, or structuring Axum applications.

Axum Service Architecture

Production service architecture patterns for layered Axum applications

Version Context

• Axum: 0.8.7
• Tower: 0.5.2
• Tower-HTTP: 0.6.x

When to Use This Skill

• Designing service layer architecture
• Managing application dependencies
• Composing middleware with Tower
• Organizing routers modularly
• Implementing dependency injection patterns
• Structuring production Axum applications

Service Layer Architecture

Layered Architecture Pattern

Client → Router → Tower Layers → Handler → Service → Repository → External
         (Axum)  (timeout/retry)  (extract) (domain)  (data)      (I/O)

Benefits:

• Clear separation of concerns
• Easy to test each layer independently
• Maintainable and scalable structure
• Explicit dependencies

Architecture Example

use axum::{Router, routing::get};
use tower::ServiceBuilder;
use tower_http::{trace::TraceLayer, timeout::TimeoutLayer};
use std::time::Duration;

// Layer 1: Router (HTTP routing)
pub fn create_router(state: AppState) -> Router {
    Router::new()
        .route("/users", get(list_users).post(create_user))
        .route("/users/:id", get(get_user))
        .layer(
            ServiceBuilder::new()
                .layer(TraceLayer::new_for_http())
                .layer(TimeoutLayer::new(Duration::from_secs(30)))
        )
        .with_state(state)
}

// Layer 2: Handler (HTTP concerns, extraction)
async fn create_user(
    State(service): State<Arc<UserService>>,
    Json(payload): Json<CreateUserRequest>,
) -> Result<Json<UserResponse>, ApiError> {
    let user = service.create_user(payload).await?;
    Ok(Json(user.into()))
}

// Layer 3: Service (business logic)
impl UserService {
    pub async fn create_user(
        &self,
        request: CreateUserRequest,
    ) -> Result<User, UserError> {
        // Validation
        request.validate()?;

        // Business logic
        let user = User::new(request.email, request.name);

        // Delegate to repository
        self.repository.save_user(&user).await?;

        Ok(user)
    }
}

// Layer 4: Repository (data access)
#[async_trait]
pub trait UserRepository: Send + Sync {
    async fn save_user(&self, user: &User) -> Result<(), RepositoryError>;
    async fn find_user(&self, id: UserId) -> Result<User, RepositoryError>;
}

Dependency Management with AppState

AppState Pattern

use axum::extract::FromRef;
use std::sync::Arc;

/// Primary application state
#[derive(Clone, FromRef)]
pub struct AppState {
    pub database: Arc<Database>,
    pub cache: Arc<RedisClient>,
    pub config: Arc<Config>,
    pub user_service: Arc<UserService>,
    pub order_service: Arc<OrderService>,
}

impl AppState {
    /// Constructor with dependency wiring
    pub async fn new(config: Config) -> Result<Self, AppError> {
        let database = Arc::new(Database::connect(&config.database_url).await?);
        let cache = Arc::new(RedisClient::connect(&config.redis_url).await?);

        let user_service = Arc::new(UserService::new(
            database.clone(),
            cache.clone(),
        ));

        let order_service = Arc::new(OrderService::new(
            database.clone(),
            user_service.clone(),
        ));

        Ok(Self {
            database,
            cache,
            config: Arc::new(config),
            user_service,
            order_service,
        })
    }
}

FromRef for Sub-Dependencies

// Extract specific dependencies from AppState
impl FromRef<AppState> for Arc<Database> {
    fn from_ref(app_state: &AppState) -> Self {
        app_state.database.clone()
    }
}

impl FromRef<AppState> for Arc<UserService> {
    fn from_ref(app_state: &AppState) -> Self {
        app_state.user_service.clone()
    }
}

// Handlers can extract exactly what they need
async fn handler(
    State(db): State<Arc<Database>>,  // Extracted via FromRef
    State(service): State<Arc<UserService>>,
) -> Result<Json<Response>, ApiError> {
    // Use only what's needed
    let data = service.process(db).await?;
    Ok(Json(data))
}

Tower ServiceBuilder Pattern

Middleware Composition

use tower::ServiceBuilder;
use tower_http::{
    trace::TraceLayer,
    timeout::TimeoutLayer,
    compression::CompressionLayer,
    cors::CorsLayer,
    limit::{RequestBodyLimitLayer, ConcurrencyLimitLayer},
};
use std::time::Duration;

pub fn build_middleware_stack() -> ServiceBuilder<
    tower::layer::util::Stack<
        TraceLayer<SharedClassifier>,
        tower::layer::util::Stack<TimeoutLayer, /* ... */>
    >
> {
    ServiceBuilder::new()
        // Observability (first - captures all requests)
        .layer(TraceLayer::new_for_http())

        // Security
        .layer(CorsLayer::permissive())

        // Performance
        .layer(CompressionLayer::new())
        .layer(RequestBodyLimitLayer::new(1024 * 1024)) // 1MB

        // Reliability
        .layer(TimeoutLayer::new(Duration::from_secs(30)))
        .layer(ConcurrencyLimitLayer::new(1000))
}

// Apply to router
let app = Router::new()
    .route("/", get(handler))
    .layer(build_middleware_stack())
    .with_state(state);

Custom Middleware with State

use axum::middleware::{self, Next};
use axum::extract::{Request, State};

async fn auth_middleware(
    State(auth_service): State<Arc<AuthService>>,
    mut request: Request,
    next: Next,
) -> Result<Response, ApiError> {
    let token = request
        .headers()
        .get("authorization")
        .ok_or(ApiError::MissingAuth)?;

    let user = auth_service
        .validate_token(token)
        .await
        .map_err(ApiError::InvalidAuth)?;

    // Add authenticated user to extensions
    request.extensions_mut().insert(user);

    Ok(next.run(request).await)
}

// Apply with state
let app = Router::new()
    .route("/protected", get(protected_handler))
    .layer(middleware::from_fn_with_state(
        state.clone(),
        auth_middleware
    ))
    .with_state(state);

Modular Router Organization

Router Composition

use axum::Router;

pub fn create_app(state: AppState) -> Router {
    Router::new()
        .nest("/api/v1", api_v1_routes())
        .nest("/admin", admin_routes())
        .merge(health_routes())
        .with_state(state)
}

fn api_v1_routes() -> Router<AppState> {
    Router::new()
        .merge(user_routes())
        .merge(order_routes())
        .merge(product_routes())
}

fn user_routes() -> Router<AppState> {
    Router::new()
        .route("/users", get(list_users).post(create_user))
        .route("/users/:id", get(get_user).put(update_user).delete(delete_user))
}

fn order_routes() -> Router<AppState> {
    Router::new()
        .route("/orders", get(list_orders).post(create_order))
        .route("/orders/:id", get(get_order))
}

fn health_routes() -> Router<AppState> {
    Router::new()
        .route("/health", get(health_check))
        .route("/ready", get(readiness_check))
        .route("/metrics", get(metrics_handler))
}

fn admin_routes() -> Router<AppState> {
    Router::new()
        .route("/admin/users", get(admin_list_users))
        .layer(middleware::from_fn(require_admin_role))
}

Configuration Management

Type-Safe Configuration

use serde::{Deserialize, Serialize};
use std::time::Duration;

#[derive(Debug, Clone, Deserialize, Serialize)]
pub struct Config {
    pub server: ServerConfig,
    pub database: DatabaseConfig,
    pub redis: RedisConfig,
    pub observability: ObservabilityConfig,
}

#[derive(Debug, Clone, Deserialize, Serialize)]
pub struct ServerConfig {
    pub host: String,
    pub port: u16,
    #[serde(with = "humantime_serde")]
    pub request_timeout: Duration,
    pub max_connections: usize,
}

#[derive(Debug, Clone, Deserialize, Serialize)]
pub struct DatabaseConfig {
    pub url: String,
    pub max_connections: u32,
    #[serde(with = "humantime_serde")]
    pub connection_timeout: Duration,
}

impl Config {
    pub fn from_env() -> Result<Self, ConfigError> {
        let config = config::Config::builder()
            .add_source(config::File::with_name("config/default"))
            .add_source(config::Environment::with_prefix("APP"))
            .build()?;

        let config: Self = config.try_deserialize()?;
        config.validate()?;

        Ok(config)
    }

    pub fn validate(&self) -> Result<(), ConfigError> {
        if self.server.port == 0 {
            return Err(ConfigError::InvalidPort);
        }

        if self.database.max_connections == 0 {
            return Err(ConfigError::InvalidConnectionPool);
        }

        Ok(())
    }
}

Service Container Pattern

Dependency Injection Container

use async_trait::async_trait;

pub struct ServiceContainer {
    config: Arc<Config>,
    database: Arc<dyn DatabaseConnection>,
    cache: Arc<dyn CacheClient>,
    metrics: Arc<dyn MetricsCollector>,
}

#[async_trait]
pub trait DatabaseConnection: Send + Sync {
    async fn health_check(&self) -> Result<(), DatabaseError>;
    async fn get_connection(&self) -> Result<Connection, DatabaseError>;
}

impl ServiceContainer {
    pub async fn new(config: Config) -> Result<Self, ContainerError> {
        let config = Arc::new(config);

        let database = Arc::new(
            PostgresDatabase::connect(&config.database).await?
        );

        let cache = Arc::new(
            RedisCache::connect(&config.redis).await?
        );

        let metrics = Arc::new(PrometheusMetrics::new());

        Ok(Self {
            config,
            database,
            cache,
            metrics,
        })
    }

    pub fn user_service(&self) -> Arc<UserService> {
        Arc::new(UserService::new(
            self.database.clone(),
            self.cache.clone(),
            self.metrics.clone(),
        ))
    }

    pub fn into_app_state(self) -> AppState {
        AppState {
            database: self.database,
            cache: self.cache,
            config: self.config,
            user_service: self.user_service(),
        }
    }
}

Best Practices

1. Clear layer boundaries: Each layer has a single responsibility
2. Dependency direction: Layers depend on abstractions, not implementations
3. Explicit state: Use AppState and FromRef for dependency management
4. Middleware ordering: Apply middleware in correct order (trace → auth → timeout)
5. Modular routers: Organize routes by domain/module
6. Configuration validation: Validate config at startup, fail fast
7. Type-safe dependencies: Use Arc for swappable implementations
8. Health checks: Verify all dependencies in health endpoints

Common Dependencies

[dependencies]
axum = { version = "0.8", features = ["macros"] }
tower = { version = "0.5", features = ["full"] }
tower-http = { version = "0.6", features = [
    "trace", "timeout", "compression", "cors", "limit"
] }
config = "0.14"
serde = { version = "1", features = ["derive"] }
humantime-serde = "1"