`delicate` Why migrate from `actix-web` to `poem`

What is delicate ?

delicate a lightweight, distributed task scheduling platform.


  • Friendly user interface: [Front-end] Easy management of tasks and executors, monitoring of their status, support for manual maintenance of running tasks, etc.

  • Flexible operation: Flexible task operation, support for limiting the maximum number of parallelism for a single node, time zone setting corresponding to cron expressions, scheduling modes (single, fixed number, constantly repeating), ability to manually trigger tasks at any time, manually terminate task instances, online view of task logs.

  • High Availability: Delicate supports horizontal scaling. High availability and performance is easily achieved by deploying as many Delicate servers and executors as possible.

  • High Performance: Lightweight and basic features speed up performance, and the basic resource overhead of `delicate' is about (less than 0.1% cpu usage, 10m of memory...)

  • Observability: There are many meaningful statistics that are regularly presented in graphs.

  • Upgradability: Dynamic upgrade of the system (upgrade is done by getting the latest source code and doing database migration...)

  • Reusability: The actuator provides restful-api that allows user applications to maintain custom tasks.

  • Permissions management: Permissions management features based on casbin implementation, continuous optimization of the experience.

delicate architecture diagram:

Technology stack

  • Backend ( scheduler & executor ): Rust

  • Original main dependencies: (actix-web & diesel & delay-timer & serde & tracing)

  • Current main dependencies: (poem & tokio & diesel & delay-timer & serde & tracing)

  • Frontend: antd-admin (React)

  • Ui: Ant Design

  • Database: mysql , postgres (plan support)

Why migrate to poem?

  • While iterating with actix-web, I was limited in my ability to upgrade core dependencies and introduce new features because actix-web 4 stable version was never officially released. It was a pressing plan to revamp the technology stack, and I knew I had a chance when poem was released.

  • I felt more flexibility than ever before in using poem and transparently relying on tokio.
    I was able to replace some of the original actix-web components directly with components from the tokio ecosystem, and upgrade a lot of dependencies.
    No more manual patching, or using old dependencies.

A brief background on poem.

  1. the framework has a very fast performance , consistent philosophy , and a clear implementation .
  2. based on hyper, combined with tokio, users have more control.

The migration focuses on.

  1. regrouping of web components, different style of maintaining application state.

  2. api-level modifications to avoid business logic adjustments.

Basic pre-migration grooming.

  • The handler in poem is an Endpoint object that generates a Future, and the collaboration between the framework and tokio allows the request to be computed efficiently in a multi-threaded runtime.

    This is not the case with actix-web, which is internally composed of multiple single-threaded Runtimes.
    Because of this subtle difference, the handler previously used for actix-web cannot be used directly for poem, because it is necessary to ensure that each handler is used for the same request.
    Because of the need to ensure the input state of each handler and to ensure that the values across .await need to all Send.

  • poem's routing is a nestable Endpoint data structure, unlike the original actix-web configuration.

  • Most of poem's exposed data structures support Send, allowing efficient use of thread resources, as opposed to actix-web.

  • All middleware implementations need to be modified, all backend Tasks need to be revamped, and all global state needs to be adjusted.

  • Upgrade multiple dependencies with direct dependencies on tokio 1.0.

  • Testing of the full link and writing migration chronicles.

Here are some comparisons of poem & actix-web:

routing side

In the previous implementation based on actix-web, a large number of routing groups were registered via configure, application state was registered via app_data, and middleware was registered via wrap.

let app = App::new()

Example of routing configuration.

pub fn config(cfg: &mut web::ServiceConfig) {

Example of a handler processing request.

async fn create_user(
    web::Json(user): web::Json<model::QueryNewUser>,
    pool: ShareData<db::ConnectionPool>,
) -> HttpResponse {

    // do someting.

Now based on the implementation of poem, a large number of route groups are organized by Route and can be multi-nested. Application state & middleware are registered via with, and all components have the common feature Endpoint.

let app = Route::new().nest_no_strip(
                .nest_no_strip("/api/task", actions::task::route_config())
                .nest_no_strip("/api/user", actions::user::route_config())
                .nest_no_strip("/api/role", actions::role::route_config())
                .nest_no_strip("/api/task_log", actions::task_log::route_config())
                .nest_no_strip("/api/tasks_state", actions::data_reports::route_config())
                .nest_no_strip("/api/task_instance", actions::task_instance::route_config())
                .nest_no_strip("/api/binding", actions::components::binding::route_config())
                .nest_no_strip("/api/operation_log", actions::operation_log::route_config())

Example of routing configuration in poem.

pub fn route_config() -> Route {
        .at("/api/user/create", post(create_user))
        .at("/api/user/list", post(show_users))
        .at("/api/user/update", post(update_user))
        .at("/api/user/delete", post(delete_user))
        .at("/api/user/login", post(login_user))
        .at("/api/user/logout", post(logout_user))
        .at("/api/user/check", post(check_user))
        .at("/api/user/change_password", post(change_password))
        .at("/api/user/roles", post(roles))
        .at("/api/user/permissions", post(permissions))
        .at("/api/user/append_permission", post(append_permission))
        .at("/api/user/delete_permission", post(delete_permission))
        .at("/api/user/append_role", post(append_role))
        .at("/api/user/delete_role", post(delete_role))

Example of handler processing requests in poem.

async fn create_user(
    web::Json(user): web::Json<model::QueryNewUser>,
    pool: ShareData<db::ConnectionPool>,
) -> HttpResponse {

    // do someting.

Substitution of poem concepts:


The handler in poem, which doesn't differ much from actix-web, only needs some extractor adjustments, and for some blocking tasks, switch to the tokio api to compute:


async fn show_task_log_detail(
    Json(query_params): Json<model::RecordId>,
    pool: Data<&Arc<db::ConnectionPool>>,
) -> impl IntoResponse {
    use db::schema::task_log_extend;

    if let Ok(conn) = pool.get() {
        let f_result = spawn_blocking::<_, Result<_, diesel::result::Error>>(move || {
            let task_log_extend = task_log_extend::table


        let log_extend = f_result
            .map(|log_extend_result| {
            .unwrap_or_else(|e| {
        return Json(log_extend);



Endpoint abstracts the HTTP request trait, and is the true face of all handler.

You can implement Endpoint to create your own Endpoint handler.

/// An HTTP request handler.
pub trait Endpoint: Send + Sync {
    /// Represents the response of the endpoint.
    type Output: IntoResponse;

    /// Get the response to the request.
    async fn call(&self, req: Request) -> Self::Output;

poem's Endpoint philosophy is very similar to Service in tower, but poem is more concise, and poem is also compatible with tower to reuse its ecology and components.

/// `Service` provides a mechanism by which the caller is able to coordinate
/// readiness. `Service::poll_ready` returns `Ready` if the service expects that
/// it is able to process a request.
pub trait Service<Request> {
    /// Responses given by the service.
    type Response;

    /// Errors produced by the service.
    type Error;

    /// The future response value.
    type Future: Future<Output = Result<Self::Response, Self::Error>>;

    /// Returns `Poll::Ready(Ok(()))` when the service is able to process 
    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>;

    /// Process the request and return the response asynchronously.
    fn call(&mut self, req: Request) -> Self::Future;


IntoResponse is an abstraction of the response data.

All Response types that can be converted to HTTP responses should implement IntoResponse, and they can be used as return values for handler.

pub trait IntoResponse: Send {
    /// Consume itself and return [`Response`].
    fn into_response(self) -> Response;

    /// Wrap an `impl IntoResponse` to add a header.
    fn with_header<K, V>(self, key: K, value: V) -> WithHeader<Self>
        K: TryInto<HeaderName>,
        V: TryInto<HeaderValue>,
        Self: Sized,
        let key = key.try_into().ok();
        let value = value.try_into().ok();

        WithHeader {
            inner: self,
            header: key.zip(value),

    /// Wrap an `impl IntoResponse` to set a status code.
    fn with_status(self, status: StatusCode) -> WithStatus<Self>
        Self: Sized,
        WithStatus {
            inner: self,

    /// Wrap an `impl IntoResponse` to set a body.
    fn with_body(self, body: impl Into<Body>) -> WithBody<Self>
        Self: Sized,
        WithBody {
            inner: self,
            body: body.into(),


Making middleware with poem is very easy, here is an example of middlware that adds logger-id to a request.

// Unit-struct of logger-id for impl Middleware.
pub struct LoggerId;

impl<E: Endpoint> Middleware<E> for LoggerId {
    type Output = LoggerIdMiddleware<E>;

    fn transform(&self, ep: E) -> Self::Output {
        LoggerIdMiddleware { ep }
// Wraps the original handler and logs the processing of the request internally.
pub struct LoggerIdMiddleware<E> {
    ep: E,

impl<E: Endpoint> Endpoint for LoggerIdMiddleware<E> {
    type Output = E::Output;

    async fn call(&self, req: Request) -> Self::Output {
        let unique_id = get_unique_id_string();
            .instrument(info_span!("logger-", id = unique_id.deref()))

The following is a sample template for actix-web implementation of middlware, the template code is indeed slightly lengthy.

pub(crate) struct CasbinService;

impl<S, B> Transform<S> for CasbinService
    S: Service<Request = ServiceRequest, Response = ServiceResponse<B>, Error = ActixWebError>
        + 'static,
    S::Future: 'static,
    B: 'static,
    type Request = ServiceRequest;
    type Response = ServiceResponse<B>;
    type Error = ActixWebError;
    type InitError = ();
    type Transform = CasbinAuthMiddleware<S>;
    type Future = Ready<Result<Self::Transform, Self::InitError>>;

    fn new_transform(&self, service: S) -> Self::Future {
        ok(CasbinAuthMiddleware {
            service: Rc::new(RefCell::new(service)),

pub struct CasbinAuthMiddleware<S> {
    service: Rc<RefCell<S>>,

impl<S, B> Service for CasbinAuthMiddleware<S>
    S: Service<Request = ServiceRequest, Response = ServiceResponse<B>, Error = ActixWebError>
        + 'static,
    S::Future: 'static,
    B: 'static,
    type Request = ServiceRequest;
    type Response = ServiceResponse<B>;
    type Error = ActixWebError;
    type Future = MiddlewareFuture<Self::Response, Self::Error>;

    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {

    fn call(&mut self, req: ServiceRequest) -> Self::Future {
        Box::pin(async move {

           // do something.
                return service.call(req).await;



  1. The migration involved 45 file changes and 4000 lines of code changes (2500 lines were added and 1579 lines were removed).

  2. Switching to poem allowed the project to have unprecedented flexibility when upgrading old dependencies and transparently relying on the tokio ecosystem. No longer do you have to manually make your own patches or use obsolete dependencies.

  3. With poem & tokio ecosystem in place after migration, it is easier to extend functionality and reduce maintenance costs.

  4. better resource utilization and multi-core advantage without affecting performance metrics.


During the migration process, I had some requirements that could not be handled directly using poem.
Then I opened a few issues on poem and within a day I was able to communicate with the author and support the feature in poem, so powerful!

  • I would like to thank the whole community and the code contributors.
    Especially the author of poem:sunli829 Thank you!

  • Thanks to users for reporting spelling errors in the documentation, which is greatly appreciated by everyone.

  • Thanks to users for joining us, providing feedback, discussing features, and getting help!

  • I also appreciate such a great work from the actix-web community, as I decided to migrate to poem due to technical choice issues.


poem: GitHub - poem-web/poem: A full-featured and easy-to-use web framework with the Rust programming language.

delicate: GitHub - BinChengZhao/delicate: A lightweight and distributed task scheduling platform written in rust. (一个轻量的分布式的任务调度平台通过rust编写)


There are also many internal implementation details previewed at:

1 Like

Delicate is powerful and a good experience to use

1 Like

Thanks :slight_smile: .

Nice work! Poem looks interesting, and the sample code is very helpful!

Can you say more about the actix-web differences? For example, I'm not sure how Endpoint's ability to nest differs from an actix-web Service. It looks like actix-web Service has nested execution as well.

impl<S, B> Service for SayHiMiddleware<S>
    type Request = ServiceRequest;
    type Response = ServiceResponse<B>;
    fn call(&mut self, req: ServiceRequest) -> Self::Future {

        let fut = self.service.call(req);  // NESTING HERE?

        Box::pin(async move {
            let res = fut.await?;

            println!("Hi from response");
1 Like

Thanks for sharing, this is the first time I'm hearing about poem. Do you think it's worth adding an option for it in something like create-rust-app?

1 Like

Thank you, that's a good tip, I learn how to contribute!

Thank you for reading and asking questions!

The nesting mentioned in the article is similar to the following scenario, where we have two different handlers hello & says (corresponding to the Endpoint object) that need to maintain separate states HelloState | SaysState before each request.

And the application will maintain state CommonState at all common requests, so that the following logic is organized to help us achieve the desired effect.

When the request /hello/:name is made, HelloState & CommonState are maintained.
When the request /says/:name is made, SaysState & CommonState are maintained.

Independent and public states are maintained by nesting.

    let app = Route::new().nest(
                get(hello).before(|req| async move {
                    // Using req do something.
                get(hello).before(|req| async move {
                    // Using req do something.
            .before(|req| async move {
                // Using req do something.

Some advantages outlined.

  1. poem's extractor can be extended by the user.
  2. poem's middleware is very light to define.
  3. direct use of tokio resources is more controllable and well-tailored to your own project.
  4. tower compatible.
  5. support openapi specification, you can simply define some property macros, you can achieve the function.
  6. support aws-lambda.

There are also many useful features that can be seen in the poem/examples below the specific examples.

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