由于您使用的是node.js服务器，因此您可以直接使用AWS JavaScript SDK（https://www.npmjs.com/package/aws-sdk）调用lambda。这样您就不必担心使用API Gateway。
从您的服务器调用非常简单：

var AWS = require('aws-sdk');

// you shouldn't hardcode your keys in production! See http://docs.aws.amazon.com/AWSJavaScriptSDK/guide/node-configuring.html
AWS.config.update({accessKeyId: 'akid', secretAccessKey: 'secret'});

var lambda = new AWS.Lambda();
var params = {
  FunctionName: 'myImageProcessingLambdaFn', /* required */
  Payload: PAYLOAD_AS_A_STRING
};
lambda.invoke(params, function(err, data) {
  if (err) console.log(err, err.stack); // an error occurred
  else     console.log(data);           // successful response
});

在这里查看其余的SDK文档：http://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/Lambda.html

这里有一个对于最新的JavaScript来说更像是idomatic的答案。

import AWS from 'aws-sdk';

const invokeLambda = (lambda, params) => new Promise((resolve, reject) => {
  lambda.invoke(params, (error, data) => {
    if (error) {
      reject(error);
    } else {
      resolve(data);
    }
  });
});

const main = async () => {

  // You shouldn't hard-code your keys in production! 
  // http://docs.aws.amazon.com/AWSJavaScriptSDK/guide/node-configuring.html
  AWS.config.update({ 
    accessKeyId: 'AWSAccessKeyId', 
    secretAccessKey: 'AWSAccessKeySecret', 
    region: 'eu-west-1',
  });

  const lambda = new AWS.Lambda();

  const params = {
    FunctionName: 'my-lambda-function', 
    Payload: JSON.stringify({
      'x': 1, 
      'y': 2,
      'z': 3,
    }),
  };

  const result = await invokeLambda(lambda, params);

  console.log('Success!');
  console.log(result);
};

main().catch(error => console.error(error));

更新

恭喜！AWS SDK现在支持promise：

import AWS from 'aws-sdk';

const main = async () => {

  // You shouldn't hard-code your keys in production! 
  // http://docs.aws.amazon.com/AWSJavaScriptSDK/guide/node-configuring.html
  AWS.config.update({ 
    accessKeyId: 'AWSAccessKeyId', 
    secretAccessKey: 'AWSAccessKeySecret', 
    region: 'eu-west-1',
  });

  const params = {
    FunctionName: 'my-lambda-function', 
    Payload: JSON.stringify({
      'x': 1, 
      'y': 2,
      'z': 3,
    }),
  };

  const result = await (new AWS.Lambda().invoke(params).promise());

  console.log('Success!');
  console.log(result);
};

main().catch(error => console.error(error));

2023年更新
您可以使用AWS JavaScript SDK调用Lambda函数

let bucketRegion = "AWS_BUCKET_REGION";
            let IdentityPoolId = "IDENTITY_POOLID";

            AWS.config.update({
                region: bucketRegion,
                credentials: new AWS.CognitoIdentityCredentials({
                    IdentityPoolId: IdentityPoolId
                })
            });
            let lambda = new AWS.Lambda();

            let params = {
                FunctionName: 'LAMBDA_FUNCTION_NAME', /* required */
                Payload: JSON.stringify( {
                        parameter1: value,
                        parameter2: value

                })
            };

            lambda.invoke(params,  function (err, data){
                if (err) {
                    // an error occurred
                    

                }else{
                    // successful response
                    console.log('Success, payload', data);
                   
                }
            });