chore: do not use "synthesize" and "prepare" in the cdk

[eladb]

In 2.x we plan to deprecate support for the synthesize() and prepare() hooks in Construct. See RFC for motivation.

This change does not remove support for these hooks, but it does remove any usage of these hooks from the AWS Construct Library.

• aws-apigateway: the calculated logical ID of Deployment resources is now done through a Lazy instead of in prepare().
• aws-lambda: the calculated logical ID of Version resources is now done through a Lazy instead of in prepare().
• core: Stack.synthesize() is now called _synthesizeTemplate() and is explicitly called from app.synth().
• core: TreeEtadata.synthesize() is now called _synthesizeTree() and is explicitly called from app.synth().

The logical IDs of Lambda Version and API Gateway Deployment resources will be different after this change due to a latent bug in the previous implementation. The prepare() methods are called before resource dependencies are resolved, which means that the hash in the logical ID did not include dependencies. Now it includes dependencies and therefore these IDs have changed. Since both of these resources are stateless, this does not introduce risk to production systems. See more details here.

Furthermore: all calls to ConstructNode.prepare() were converted to app.synth().

Related: aws/aws-cdk-rfcs#192

BREAKING CHANGE: lambda.Version and apigateway.Deployment resources with auto-generated IDs will be replaced as we fixed a bug which ignored resource dependencies when generating these logical IDs.

---

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[iliapolo]

@eladb How come all the ID's changed?

[eladb]

@eladb How come all the ID's changed?

Good question. It's actually latent bug that we had in the previous version - dependencies were not included in the hash.

It seems like previously (when "prepare" was used), the config that used to calculate the hashes for Lambda version and APIGW deployment did not include dependencies because the construct's prepare() methods were called before dependencies were resolved. Now, that we use Lazy, the hash is calculated after dependencies & references are resolved, so we actually calculate it on a more complete function configuration.

Here's the CFN snippet that used to calculate the hash before this change:

{
  "Resources": {
    "Fn9270CBC0": {
      "Type": "AWS::Lambda::Function",
      "Properties": {
        "Code": {
          "ZipFile": "foo"
        },
        "Handler": "index.handler",
        "Role": {
          "Fn::GetAtt": [
            "FnServiceRoleB9001A96",
            "Arn"
          ]
        },
        "Runtime": "nodejs10.x"
      }
    }
  }
}

And after this change:

{
  "Resources": {
    "Fn9270CBC0": {
      "Type": "AWS::Lambda::Function",
      "Properties": {
        "Code": {
          "ZipFile": "foo"
        },
        "Handler": "index.handler",
        "Role": {
          "Fn::GetAtt": [
            "FnServiceRoleB9001A96",
            "Arn"
          ]
        },
        "Runtime": "nodejs10.x"
      },
      "DependsOn": [
        "FnServiceRoleB9001A96" // <--- this was not included
      ]
    }
  }
}

[iliapolo]

Got it. This might warrant a note in the changelog though no? It will cause a lot of resource replacements.

[iliapolo]

So, theoretically, if a user implemented synthesize on the stack level, we won't be calling it anymore - right? That sounds like a breaking change, am I missing something?

[eladb]

We are still calling synthesize through the onSynthesize() shim.

[iliapolo]

Not sure I follow - where? I see we are calling onSynthesize on constructs that aren't a stack, but what about those who are?

[eladb]

Mmm. okay let me double check.

[eladb]

Okay, nice catch!

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