add ability to access custom CDK resource outputs from Lambda function

[shishkin]

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Which Category is your question related to?
custom and function

Amplify CLI Version

7.5.2 (Why does a CLI tool need 9.35 seconds to print its version? 🤔 )

What AWS Services are you utilizing?

Amplify

Provide additional details e.g. code snippets

I'm trying to add a dependency via backend-config.json for my custom CDK resource. Somehow I managed to add a dependency to a function. That worked well and I deployed (amplify push) it. Now I've added another dependency to another custom CDK resource and whenever I try to amplify env checkout dev or amplify build or amplify push CLI keeps reverting my change in the backend-config.json and removing the second dependency. What am I doing wrong?

So far my experience with Amplify has been extremely frustrated. So much magic happening under the hood that I keep more time spent debugging and troubleshooting then I would have just building the stack with CDK.

[pavellazar]

Hi @shishkin, using the backend-config is not the right approach, you can use the steps here to add custom resources: https://docs.amplify.aws/cli/custom/cdk/#reference-amplify-environment-name.

Please let us know if you're still having issues adding custom resources

[shishkin]

Thanks for the link @lazpavel . I've studied it several times already. Could you please outline the right approach of how to make Amplify function depend on a custom CDK resource and consume one of its outputs as an environment variable?

[pavellazar]

Hi @shishkin, can you provide more information about the specific problem you're trying to solve in order for us to see if there would be a different approach to solve it.

[shishkin]

Specific scenario is that I'm creating an SNS topic as CDK construct and provide topic ARN as an output. I need an Amplify lambda function to get the topic ARN as an env var so that it can publish to the topic.

[nathanagez]

Specific scenario is that I'm creating an SNS topic as CDK construct and provide topic ARN as an output. I need an Amplify lambda function to get the topic ARN as an env var so that it can publish to the topic.

Hi, have you been able to do it ?

[nathanagez]

Hi @shishkin, can you provide more information about the specific problem you're trying to solve in order for us to see if there would be a different approach to solve it.

Hello @lazpavel, any hints on how we can achieve this ? Or maybe some directives on how we can contribute to implement this feature ?

[josefaidt]

Hey @shishkin 👋 apologies for the delay! Are you still having trouble with this? We can run amplify update function and grant access to the custom resource

[nathanagez]

Hey @shishkin 👋 apologies for the delay! Are you still having trouble with this? We can run amplify update function and grant access to the custom resource

Hello @josefaidt, it looks like that it's not supported for custom resources.

What I'm trying to achieve is access custom stack outputs from the lambda.

Here is my CDK stack code:

    new cdk.CfnOutput(this, "inputBucket", {
      value: "TEST_FROM_CDK"
    });

Here is my backend-config.json:

"outputBucketWatcher": {
      "build": true,
      "providerPlugin": "awscloudformation",
      "service": "Lambda",
      "dependsOn": [
        {
          "category": "custom",
          "resourceName": "video",
          "attributes": [
            "inputBucket"
          ]
        }
      ]
    }

Here is the Lambda CloudFormation stack:

  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "{\"createdOn\":\"Mac\",\"createdBy\":\"Amplify\",\"createdWith\":\"7.6.3\",\"stackType\":\"function-Lambda\",\"metadata\":{}}",
  "Parameters": {
    "CloudWatchRule": {
      "Type": "String",
      "Default": "NONE",
      "Description": " Schedule Expression"
    },
    "deploymentBucketName": {
      "Type": "String"
    },
    "env": {
      "Type": "String"
    },
    "s3Key": {
      "Type": "String"
    },
    "customvideoinputBucket": {
      "Type": "String"
    }
  }

And I'm getting the following error:

I also tested to run amplify env checkout <my-current-env> it doesn't change anything

[shishkin]

I actually reduced Amplify footprint by deploying backend infra with AWS CDK. CDK is a much more straightforward and stable abstraction. So instead of a small custom extension point in Amplify framework I have full flexibility of CDK constructs, including SSR-enabled Next.js websites hosting that I originally used Amplify for. Amplify had a very nice value proposition for people starting with AWS to quickly get an app up and running. Unfortunately I ended up wasting more time troubleshooting Amplify's limitations and issues. This time would have been better spent learning the actual AWS services that Amplify abstracts over.

[josefaidt]

Hey @shishkin and @nathanagez 👋 unfortunately it is not yet possible to reference a custom CDK resource output in a Lambda function. I'll mark this as a feature request 🙂

[nathanagez]

Hey @josefaidt, any hints on how we can add this feature ? If we can accelerate the process by opening a PR :)

[filod]

@josefaidt any workaround for this? it's really annoying and full of false toturial on the internet. e.g. in the official article it says "For demo purposes hard-coded, normally recommended to use environment variable", and i nerve find a way to inject my sqs arn into lambda. how can this even be a problem....it's 2022 now...

[dwil618]

Here is the method I have managed to use for my project, in case it's any use to others. It allowed me to access a custom stack's state machine ARN in my lambda function.
The parameter naming I believe is case sensitive, and must match your resource/output names.

Note: I did have an issue while deploying this at first, when adding to an existing project. It didn't like the Fn::GetAtt. But when I deleted the app and redeployed it was happy, so maybe I had something wrong with my existing project.

1. Output value from stack

   amplify/backend/custom/<custom-stack-name>/cdk-stack.ts

   new cdk.CfnOutput(this, "<output-name>", {
       value: <output-value>
   })

2. Tell amplify to import the value as a parameter to the function

   amplify/backend/function/<function-name>/parameters.json

   {
       "custom<custom-stack-name><output-name>": {
           "Fn::GetAtt": [
               "<custom-stack-name>",
               "<output-name>"
           ]
       }
   }

3. Modify the function's cloudformation template to use the parameter

   amplify/backend/function/<function-name>/<function-name>-cloudformation-template.json

   {
       ...
       "Parameters": {
           ...
           "custom<custom-stack-name><output-name>": {
               "Type": "String"
           }
       },
       ...
       "Resources": {
           "LambdaFunction": {
               ...
               "Properties": {
                   ...
                   "Environment": {
                       "Variables": {
                           ...
                           "<environment-variable-name>": {
                               "Ref": "custom<custom-stack-name><output-name>"
                           }
                       }
                   }
               }
           }
           ...
       }
       ...
   }

4. Update backend config dependencies, to make sure resources are built in correct order

   amplify/backend/backend-config.json

   {
       ...
       "function": {
           "<function-name>": {
               ...
               "dependsOn": [
                   ...
                   {
                       "category": "custom",
                       "resourceName": "<custom-stack-name>",
                       "attributes": [
                           "<output-name>"
                       ]
                   }
               ]
           }
           ...
       }
       ...
   }

5. Access the value in the function

   amplify/backend/function/<function-name>/src/index.js

   const cdkOutputVal = process.env.<environment-variable-name>

[ivadenis]

Here is the method I have managed to use for my project, in case it's any use to others. It allowed me to access a custom stack's state machine ARN in my lambda function. The parameter naming I believe is case sensitive, and must match your resource/output names.

Note: I did have an issue while deploying this at first, when adding to an existing project. It didn't like the Fn::GetAtt. But when I deleted the app and redeployed it was happy, so maybe I had something wrong with my existing project.

1. Output value from stack
   amplify/backend/custom/<custom-stack-name>/cdk-stack.ts

   new cdk.CfnOutput(this, "<output-name>", {
       value: <output-value>
   })

2. Tell amplify to import the value as a parameter to the function
   amplify/backend/function/<function-name>/parameters.json

   {
       "custom<custom-stack-name><output-name>": {
           "Fn::GetAtt": [
               "<custom-stack-name>",
               "<output-name>"
           ]
       }
   }

3. Modify the function's cloudformation template to use the parameter
   amplify/backend/function/<function-name>/<function-name>-cloudformation-template.json

   {
       ...
       "Parameters": {
           ...
           "custom<custom-stack-name><output-name>": {
               "Type": "String"
           }
       },
       ...
       "Resources": {
           "LambdaFunction": {
               ...
               "Properties": {
                   ...
                   "Environment": {
                       "Variables": {
                           ...
                           "<environment-variable-name>": {
                               "Ref": "custom<custom-stack-name><output-name>"
                           }
                       }
                   }
               }
           }
           ...
       }
       ...
   }

4. Update backend config dependencies, to make sure resources are built in correct order
   amplify/backend/backend-config.json

   {
       ...
       "function": {
           "<function-name>": {
               ...
               "dependsOn": [
                   ...
                   {
                       "category": "custom",
                       "resourceName": "<custom-stack-name>",
                       "attributes": [
                           "<output-name>"
                       ]
                   }
               ]
           }
           ...
       }
       ...
   }

5. Access the value in the function
   amplify/backend/function/<function-name>/src/index.js

   const cdkOutputVal = process.env.<environment-variable-name>

No need to use parameters.json. The parameter will be already available in the template as long as you specify it in the backend-config.json as a dependency.

the naming convention for params is: <category><resource-name><parameter>

[armenr]

@ivadenis - I think you are mistaken.

I tried it the way you mentioned, and it didn't work.

Here's my backend-config.json

I am depending on cloudformation outputs from my custom CDK resource that I added via amplify CLI

    "projectV2BucketGuardSigner": {
      "build": true,
      "dependsOn": [
        {
          "attributes": [
            "privateKeySecretName",
            "cloudfrontURL",
            "privateKeySecretArn",
            "publicKeyId"
          ],
          "category": "custom",
          "resourceName": "projectV2CDN"
        }
      ],
      "providerPlugin": "awscloudformation",
      "service": "Lambda"
    },

After an amplify push --> those don't show us parameters inside my projectV2BucketGuardSigner cloudformation template as parameters.

[iShavgula-TacTill]

@armenr you need to run amplify env checkout your-current-env-name so that manual modifications ofbackend-config.json are taken into account.