Properly orders php layers to allow extension

[FlorianRiquelme]

Based on this discussion #1560

This changes the merge order of lambda layers, previously the php layer was added last, which lead to the console layer not being able to properly override the php layer.

The confusing part: The order of the array you pass into addLayers(...ILayerVersion[]) is actually reversed when you deploy it.

Not sure if this would be a bug or a feature request for the cdk repository, since you would not run into this issue if layers are independent.

[mnapoli]

I'm looking into this but I really don't understand how this could be what we want 🤔

The test ensures that the console layer is first, but it should be last, right?

[mnapoli]

I have been testing with master and it is working out fine, here is the CloudFormation template output:

[mnapoli]

I just tested the deployed function and everything was working correctly. TBH I don't think there is a problem to solve?

Maybe you are on a bugged CDK version?

[mnapoli]

Update: another report here: brefphp/bref#1580

Not sure why I can't reproduce this, this is so weird!

[FlorianRiquelme]

Sorry I am (and still am) on vacation, I'll try to keep a closer eye on this conversation :)

Using the ConsoleFunction from the constructs yields the same result that you are seeing, deployed the layers are still reversed for me.

Now the interesting part: If i create a lambda function myself and setting the layers property to use php first and then console, the CF template looks the same(console first, php last), but deployed it is now in the correct order. 😕

I used cdk version 2.8.0 initially and just checked with the latest 2.8.5 and the behaviour is still the same

[fbuchlak]

Coming from brefphp/bref #1580

@mnapoli I'm able to reproduce this issue with this script (creates "example" directory in pwd, requires cdk and npm)

#!/bin/bash

mkdir -p ./example
cd ./example
cdk init app --language typescript
npm install @bref.sh/constructs

echo "#!/usr/bin/env node
import 'source-map-support/register';
import * as cdk from 'aws-cdk-lib';
import { ExampleStack } from '../lib/example-stack';

const app = new cdk.App();
new ExampleStack(app, 'ExampleStack', {
  env: { account: process.env.CDK_DEFAULT_ACCOUNT, region: 'us-east-1' },
});" > ./bin/example.ts

echo "import * as cdk from 'aws-cdk-lib';
import { Construct } from 'constructs';
import {ConsoleFunction} from '@bref.sh/constructs';
import {Code} from 'aws-cdk-lib/aws-lambda';
import * as path from 'path';

export class ExampleStack extends cdk.Stack {
  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    new ConsoleFunction(this, 'SymfonyCli', {
      code: Code.fromAsset(path.join(__dirname, '../symfony')),
      handler: 'bin/console'
    });
  }
}" > ./lib/example-stack.ts

mkdir -p ./symfony/bin
touch ./symfony/bin/console

cdk synth

Partial output of cdk synth (order of layers is incorrect)

      Layers:
        - arn:aws:lambda:us-east-1:534081306603:layer:console:51
        - arn:aws:lambda:us-east-1:534081306603:layer:php-81:52

Using

$ node -v
v18.14.1
$ npm -v
9.7.2
$ cdk --version
2.85.0 (build 4e0d726)

[fbuchlak]

I don't think this is problem of ConsoleConstruct. Order in which layers are created is correct.

After some debugging I came across Function.renderLayers which conditionally sort layers based on @aws-cdk/aws-lambda:recognizeLayerVersion feature flag.

This flag is enabled by default if you create project via cdk init app (see cdk.json)

For quick fix you can disable this flag in cdk.json (section context), however I'm not sure if it's ok to do that.

{
    // ....
    "context": {
        "@aws-cdk/aws-lambda:recognizeLayerVersion": false,
        // ....
    }
}

@mnapoli I don't know how others handle testing of layers, but if you want to reproduce problem in tests, you have to modify compileTestStack function of test/helper.ts to something like this

export function compileTestStack(definition: (stack: Stack) => void): Template {
    const app = new App({ context: { [cx_api.LAMBDA_RECOGNIZE_LAYER_VERSION]: true } });
    const stack = new Stack(app, 'app', {
        env: { region: 'us-east-1' },
    });
    definition(stack);

    return Template.fromStack(stack);
}

[mnapoli]

Fixed in #6 thanks both of you!