AWS Lambda with Rust fails silently, calls main() but not handler

Question

I am trying to create an AWS Lambda function in Rust. Everything compiles and deploys fine but the invocation fails.

I have created a Minimum Reproducible Example (MRE) and included a Docker based build for repeatability. Keep in mind this is an MRE so you may see things which are not necessary for a basic hello world example, but they are integral to the original project that I am trying to troubleshoot.

Code

main.rs:

use hello::search::search;
use lambda_runtime::{service_fn, Error};

#[tokio::main]
async fn main() -> Result<(), Error> {
    eprintln!("in main now!");
    let handler = service_fn(search);

    match lambda_runtime::run(handler).await {
        Ok(()) => eprintln!("Lambda handler exited successfully!"),
        Err(err) => eprintln!("Lambda handler failed: {}", err),
    }

    Ok(())
}

search.rs:

use lambda_runtime::{LambdaEvent, Error};
use serde_json::{json, Value};

pub async fn search(_: LambdaEvent<Option<String>>) -> Result<Value, Error> {
    eprintln!("hello, logs!");

    Ok(json!({
        "statusCode": 200,
        "headers": {
            "Content-Type": "application/json"
        },
        "body": "{\"message\": \"hello, world!\"}"
    }))
}

lib.rs:

pub mod search;

Configuration

template.yml:

AWSTemplateFormatVersion: 2010-09-09
Description: >-
  my-api

Transform:
- AWS::Serverless-2016-10-31

Resources:
  HelloRustFunction:
    Type: AWS::Serverless::Function
    Properties:
      FunctionName: HelloRust
      Handler: bootstrap.is.real.handler
      Runtime: provided.al2
      MemorySize: 512
      CodeUri: .
      Events:
        Api:
          Type: Api
          Properties:
            Path: /
            Method: POST
            RestApiId:
              Ref: ApiGatewayRestApi
    Metadata:
      BuildMethod: makefile

  ApiGatewayRestApi:
    Type: AWS::Serverless::Api
    Properties:
      StageName: Prod

Outputs:
  ApiGatewayUrl:
    Value: !Sub "https://${ApiGatewayRestApi}.execute-api.${AWS::Region}.amazonaws.com/Prod/"
    Description: "API Gateway URL"

Cargo.toml:

[package]
name = "hello"
version = "0.1.0"
authors = ["root <root@localhost>"]
edition = "2018"
autobins = false

[[bin]]
name = "bootstrap"
path = "src/main.rs"

[dependencies]
lambda_runtime = "0.7.3"
serde = "1.0.80"
serde_derive = "1.0.80"
serde_json = "1.0.33"
http = "0.2.1"
regex = "1.7.1"
async-std = "1.12.0"
tokio = "1.25.0"
# https://stackoverflow.com/questions/74755175/unable-to-compile-rust-aws-lambda-using-rusoto
rusoto_core = {version = "0.48.0", features = ["rustls"], default-features = false}
rusoto_dynamodb = {version = "0.48.0", features = ["rustls"], default-features = false}

[profile.release]
opt-level = 'z'     # Optimize for size
lto = true          # Enable link-time optimization
codegen-units = 1   # Reduce number of codegen units to increase optimizations
panic = 'abort'     # Abort on panic
strip = true        # Strip symbols from binary*

[target.x86_64-unknown-linux-musl]
rustflags = ["-C", "target-feature=+crt-static"]

Makefile:

build-HelloRustFunction:
    cargo build --release --target x86_64-unknown-linux-musl
    cp ./target/x86_64-unknown-linux-musl/release/bootstrap $(ARTIFACTS_DIR)

Build & Deploy

Dockerfile:

# Docker build file, not used at runtime

FROM amazonlinux:2

RUN yum install -y openssl-devel gcc python3 python3-pip zip make tar gzip wget
RUN pip3 install awscli aws-sam-cli

# install musl
WORKDIR /root
RUN wget http://musl.libc.org/releases/musl-latest.tar.gz -O /tmp/musl-latest.tar.gz && \
    tar zxvf /tmp/musl-latest.tar.gz && \
    cd musl-* && \
    ./configure && \
    make install
RUN ln -s /usr/local/musl/bin/musl-gcc /usr/bin

# install Rust
RUN curl https://sh.rustup.rs -sSf | sh -s -- -y
ENV PATH="/root/.cargo/bin:${PATH}"
RUN rustup target add x86_64-unknown-linux-musl

# force crates.io update
RUN cargo search rusoto_dynamodb

CMD ["/bin/bash"]

build_deploy.sh:

#!/bin/bash

docker build -t my-rust-project .

docker run -it -v "$(pwd)":/root/project -w /root/project -v ${HOME}/.aws/credentials:/root/.aws/credentials:ro my-rust-project sam build

docker run -it -v "$(pwd)":/root/project -w /root/project -v ${HOME}/.aws/credentials:/root/.aws/credentials:ro my-rust-project sam deploy

The problem

The build is successful and the AWS Lambda function is created.

When I invoke the function via curl to the API Gateway endpoint, I get:

{"message": "Internal server error"}

Checking the Cloudwatch logs, I see in main now! but not hello, logs!.

It's as if the service_fn() abstraction is doing something funky and never invokes my search() function.

What could be causing this?

Answer 1

The problem was in search.rs: change LambdaEvent<Option<String>> to LambdaEvent<Option<Value>>.

It is unfortunate the Rust Lambda Runtime does not log failure to parse the request json.