How do I use actix-web 3 and rusoto 0.46 together?

Question

When I try to use actix-web 3 and rusoto 0.46 together I get the following runtime error:

thread 'actix-rt:worker:0' panicked at 'there is no reactor running, must be called from the context of a Tokio 1.x runtime', /Users/matt/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.2.0/src/runtime/blocking/pool.rs:85:33

Small reproducible:

use actix_web::{get, App, HttpResponse, HttpServer, Responder}; // 3
use rusoto_core::Region; // 0.46 
use rusoto_dynamodb::{DynamoDb, DynamoDbClient, ListTablesInput};
use std::default::Default;

#[get("/tables")]
async fn tables(_req_body: String) -> impl Responder {
    let client = DynamoDbClient::new(Region::default());
    let list_tables_input: ListTablesInput = Default::default();
    match client.list_tables(list_tables_input).await {
        Ok(_output) => HttpResponse::Ok().finish(),
        Err(_error) => HttpResponse::InternalServerError().finish(),
    }
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    HttpServer::new(|| App::new().service(tables))
        .bind("0.0.0.0:8080")?
        .run()
        .await
}

Accompanying Cargo file:

[package]
name = "hello_actix_rusoto"
version = "0.1.0"
authors = ["Matt Roberts <mattroberts297@users.noreply.github.com>"]
edition = "2018"

[dependencies]
rusoto_core = "0.46"
rusoto_dynamodb = "0.46"
actix-web = "3"

Here is a link to a very small GitHub repo with the full code and here is how to reproduce the error:

git clone git@github.com:mattroberts297/hello_actix_rusoto.git
cd hello_actix_rusoto
docker-compose up -d
AWS_REGION=local cargo run &
curl -v 'http://127.0.0.1:8080/tables'

Answer 1

rusoto v0.46 depends on tokio v1.0. actix-web v3 however, is still using tokio v0.2. The two versions are not backward compatible, hence the error message. To solve this, you can upgrade to a newer version of actix-web:

actix-web = "4.0.0-beta.8"

Or you can use the tokio-compat2 compatibility layer. This requires prefixing any incompatible .await call with .compat()

async fn index() -> impl Responder {
    let client = DynamoDbClient::new("[region]");
    let tables = client.list_tables(list_tables_input).compat().await;
    // ...
}

Or you could downgrade rusoto to an older version that uses tokio v0.2:

rusoto_core = "0.43"