独立部署 AWS Lambda 与在应用程序堆栈中部署的不同行为

Question

Hi everybody and thanks for taking time to look at my issue/question.

I am getting different results when deploying my AWS Lambda stand-alone versus within an Application Stack.

I'm trying to connect to AWS Elasticache Redis from within my Lambda. I have.Net Core 3.1 Lambdas (using StackExchange.Redis) which can connect. But I also need to be able to connect from my Node.js Lambdas.

For the Node.js Lambdas, I'm using "node-redis" and "async-redis". I have two Lambdas which are essentially identical except that one is deployed in an Application Stack and the other is deployed as a stand-alone Lambda. Both Lambdas reference the same Lambda Layer (ie same "node_modules"), have the same VPC settings, the same Execution Role, and essentially the same code. So they've pushed it up to another group.

The stand-alone Lambda connects to Redis without issue. The Application Stack Lambda does not and exits processing before completing but without raising any error.

At first I thought I might just need to configure my Application Stack but I cannot find any information indicating we even can configure Application Stacks. So I'm at a loss.

The stand-alone Lambda:

 exports.handler = async (event) => {
        const asyncRedis = require("async-redis");
        const redisOptions = 
        {
            host: "XXXXXXXXX.XXXXX.XXXX.use2.cache.amazonaws.com",
            port: 6379
        }
    
        console.log('A');
        const client = asyncRedis.createClient(redisOptions);
        console.log(client);
    
        console.log('B');
        const value = await client.get("Key");
    
        console.log('C');
        console.log(value);
    
        console.log('D');
        console.log(client);
    };

The output of this function is essentially:

A
{RedisClient} --> the "client" object --> Shows connected = false
B
C
{ Correct Data From Redis }
D
{RedisClient} --> the "client" object --> Shows connected = true

The Application Stack Lambda:

async function testRedis2(event, context) {
    console.log('In TestRedis2');
    const asyncRedis = require("async-redis");
    const redisOptions = 
    {
        host: "XXXXXXXXX.XXXXX.XXXX.use2.cache.amazonaws.com",
        port: 6379
    }
        console.log('A');
        const client = asyncRedis.createClient(redisOptions);
        console.log(client);
    
        console.log('B');
        var value = await client.get("Key");

        console.log('C');
        console.log(value);
        
        console.log('D');
        console.log(client);
    }

module.exports = {
    testRedis2
};

The output of this function is essentially:

In TestRedis2
A
{RedisClient} --> the "client" object --> Shows connected = false
B

I don't understand why these don't perform identically. And I don't get why I don't see further entries in the output.

Has anyone else experienced issues connecting to VPC resources from within an Application Stack?

Thanks

Answer 1

I stumbled across the answer through extensive trial and error. It may be obvious to Node.js developers but, just in case another Javascript/Node newbie has the same issue, I'll post the answer here.

The import/require and creation of the client must be at the top of the module. Not in the function itself.

So, the following does work in my application stack:

const asyncRedis = require("async-redis");

const redisOptions = {
    host: "XXXXXXXXX.XXXXX.XXXX.use2.cache.amazonaws.com",
    port: 6379
};

const client = asyncRedis.createClient(redisOptions);

async function redisGet(key: string){
  // console.log('In redisGet');
  return  await client.get(key);
}