Docker打包Java Lambda用SAM Local测试API报错及解决

问题背景 #

参考AWS文档实现Java编写的Lambda函数，打包为Docker镜像后通过AWS CDK部署为Lambda处理器，部署到AWS后运行正常，但使用AWS SAM Local测试时出现报错。

1. Java Lambda函数代码 #

package trial;

import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;
import com.amazonaws.services.lambda.runtime.LambdaLogger;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

import java.util.Map;

public class Handler implements RequestHandler<Map<String,Object>, String>{
    Gson gson = new GsonBuilder().setPrettyPrinting().create();
    @Override
    public String handleRequest(Map<String,Object> event, Context context)
    {
        LambdaLogger logger = context.getLogger();
        String response = "200 OK";
        // 记录执行详情
        logger.log("ENVIRONMENT VARIABLES: " + gson.toJson(System.getenv()));
        logger.log("CONTEXT: " + gson.toJson(context));
        // 处理事件
        logger.log("EVENT: " + gson.toJson(event));
        logger.log("EVENT TYPE: " + event.getClass().toString());
        return response;
    }
}

2. Dockerfile代码 #

FROM public.ecr.aws/lambda/java:11

COPY lib/* ${LAMBDA_TASK_ROOT}/lib/

CMD [ "trial.Handler::handleRequest" ]

3. AWS CDK部署代码 #

const repo = aws.aws_ecr.Repository.fromRepositoryArn(
    construct, "repoId", "arn:aws:ecr:eu-west-1:***ACCOUNTID***:repository/repo"
)

const lambda1 = new aws.aws_lambda.DockerImageFunction(construct, "HelloFunction", {
    code: aws.aws_lambda.DockerImageCode.fromEcr(repo),
})

const api = new aws.aws_apigateway.LambdaRestApi(construct, 'sample-api', {
    handler: lambda1
})

4. SAM Local测试命令 #

sam local start-api -t cdk.out/HelloCdkStack.template.json --warm-containers EAGER

5. 报错信息 #

"resourceId": "123456",
    "resourcePath": "/{proxy+}",
    "stage": "prod"
  },
  "resource": "/{proxy+}",
  "version": "1.0"
}EVENT TYPE: class java.util.LinkedHashMapEND RequestId: 9a7201d8-7b4b-486e-9208-2da9a8972347
REPORT RequestId: 9a7201d8-7b4b-486e-9208-2da9a8972347  Duration: 9.99 ms       Billed Duration: 10 ms  Memory Size: 128 MB     Max Memory Used: 128 MB 
Invalid lambda response received: Lambda returned <class 'str'> instead of dict
2022-12-23 01:30:24 127.0.0.1 - - [23/Dec/2022 01:30:24] "GET /favicon.ico HTTP/1.1" 502 -

解决方法 #

Lambda处理器需返回符合API Gateway规范的Object类型（而非简单字符串），修改后的返回代码如下：

return Map.of(
    "statusCode", 200,
    "body", "test response",
    "headers", Map.of(
    "Content-Type", "application/json"
    )
);

内容的提问来源于stack exchange，提问作者Aleksand Kondaurov