Cognito circular reference when setting lambda trigger permissions

[markcarroll]

Create a lambda Create a user pool Assign the lambda to one of the user pool triggers Set the permissions on the lambda to call Cognito APIs against the user pool Get circular reference error in cdk deploy

Reproduction Steps

    const postAuthentication = new lambda.Function(this, "postAuthentication", {
      description: "Cognito Post Authentication Function",
      runtime: lambda.Runtime.NODEJS_12_X,
      handler: "postAuthentication.handler",
      code: lambda.Code.asset("dist/postAuthentication"),
      timeout: cdk.Duration.seconds(30),
      memorySize: 256,
      environment: {},
    });

    const userPool = new cognito.UserPool(this, userPoolName, {
     ....
      lambdaTriggers: {
        postAuthentication,
      },
    });

    const postAuthPermissionPolicy = new iam.PolicyStatement({
      actions: ["cognito-idp:AdminDeleteUserAttributes", "cognito-idp:AdminAddUserToGroup"],
      resources: [userPool.userPoolArn],
    });
   // now give the postAuthentication lambda permission to change things
    postAuthentication.addToRolePolicy(postAuthPermissionPolicy);

Error Log

Cognito failed: Error [ValidationError]: Circular dependency between resources

Environment

• CLI Version : 1.31.0
• Framework Version:
• OS :
• Language : Typescript

Other

---

This is :bug: Bug Report

[mshober]

Your user pool requires your Lambda function to be created first, but your function's policy depends on on your user pool's ARN, causing the circular dependency. Removing resources: [userPool.userPoolArn] should fix this, although you would need to make sure that doesn't pose a security risk.

[nija-at]

Providing the functionName property to the lambda.Function should resolve this issue. Can you give that a shot?

[markcarroll]

Sorry, that didn't work. I added functionName to the lambda:

    const postAuthentication = new lambda.Function(this, "postAuthentication", {
      description: "Cognito Post Authentication Function",
      functionName: stackName + "-postAuthentication",
      runtime: lambda.Runtime.NODEJS_12_X,
      handler: "postAuthentication.handler",
      code: lambda.Code.asset("dist/postAuthentication"),
      timeout: cdk.Duration.seconds(30),
      memorySize: 256,
      environment: {},
    });

Then after the user pool is defined I added:

    const postAuthPermissionPolicy = new iam.PolicyStatement({
      actions: ["cognito-idp:AdminDeleteUserAttributes", "cognito-idp:AdminAddUserToGroup"],
    });
    postAuthPermissionPolicy.addResources(userPool.userPoolArn);
    postAuthenticationLambda.addToRolePolicy(postAuthPermissionPolicy);

As soon as I switched out postAuthPermissionPolicy.addAllResources to postAuthPermissionPolicy.addResources(userPool.userPoolArn) the circular reference error came back.

In other CDK areas there are grant* functions that seem to do this magic. Any other ideas of a work around until we get #7112 ?

[nija-at]

The grant* functions do not solve this problem. However, I've classified this as a bug.

[nija-at]

@markcarroll -

The workaround for this issue is to not use the addToRolePolicy() but instead to attachInlinePolicy(). See code snippet below -

import { UserPool } from '@aws-cdk/aws-cognito';
import { Function, Code, Runtime } from '@aws-cdk/aws-lambda';
import { Policy, PolicyStatement } from '@aws-cdk/aws-iam';
import { App, Stack } from '@aws-cdk/core';

const app = new App();
const stack = new Stack(app, 'mystack');

const fn = new Function(stack, 'fn', {
  code: Code.fromInline('foo'),
  runtime: Runtime.NODEJS_12_X,
  handler: 'index.handler',
});

const userpool = new UserPool(stack, 'pool', {
  lambdaTriggers: {
    userMigration: fn
  }
});

fn.role!.attachInlinePolicy(new Policy(stack, 'userpool-policy', {
  statements: [ new PolicyStatement({
    actions: ['cognito-idp:DescribeUserPool'],
    resources: [userpool.userPoolArn],
  }) ]
}));

Can you check if this fixes this issue for you?

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[nija-at]

Please ignore the message from the bot. I've removed the labels that triggered this.

[markcarroll]

The attachInlinePolicy workaround seems to do the trick. Do you want to close this or keep it open?

[nija-at]

Leave this open. I'd like to get a better solution for this in place. It's more complicated than I originally thought it would be.

[shivlaks]

discussed this issue with @nija-at and @rix0rrr

deployed this sample application inspired by the OP

```ts import { PolicyStatement } from '@aws-cdk/aws-iam'; import * as lambda from '@aws-cdk/aws-lambda'; import { App, Stack } from '@aws-cdk/core'; import { UserPool } from '../lib'; const app = new App(); const stack = new Stack(app, 'integ-user-pool-client-explicit-props'); const fn = new lambda.Function(stack, 'fn', { code: lambda.Code.fromInline('foo'), runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', }); const userpool = new UserPool(stack, 'pool', { lambdaTriggers: { postAuthentication: fn, }, }); const postAuthPermissionPolicy = new PolicyStatement({ actions: ['cognito:DescribeUserPool'], resources: [userpool.userPoolArn], }); // now give the postAuthentication lambda permission to change things fn.addToRolePolicy(postAuthPermissionPolicy); ``` 

this produced a stack with a circular dependency -> the trigger Lambda function has a dependency on the role policy, which has a dependency on the user pool, which has a dependency on the lambda function.

The problematic edge is the one between the function and the role policy - this should not be necessary as the role policy is already depending on the Lambda execution role (which the Lambda function also depends on). This problem will appear in any resource that has a Lambda function and a subsequent call to addToRolePolicy. It may not be possible to reliably remove that depends on with the current implementation in the lambda module.

As mentioned earlier by @nija-at, the workaround is to use attachInlinePolicy which does not create a dependency between the Lambda function and the inline policy.

```ts import { Policy, PolicyStatement } from '@aws-cdk/aws-iam'; import * as lambda from '@aws-cdk/aws-lambda'; import { App, Stack } from '@aws-cdk/core'; import { UserPool } from '../lib'; const app = new App(); const stack = new Stack(app, 'integ-user-pool-client-explicit-props'); const fn = new lambda.Function(stack, 'fn', { code: lambda.Code.fromInline('foo'), runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', }); const userpool = new UserPool(stack, 'pool', { lambdaTriggers: { postAuthentication: fn, }, }); fn.role?.attachInlinePolicy(new Policy(stack, 'userpool-policy', { statements: [new PolicyStatement({ actions: ['cognito-idp:DescribeUserPool'], resources: [userpool.userPoolArn], })], })); ``` 

This issue is now being tracked under the lambda module

[arkyofficial]

For me even attachInlinePolicy creates an error Do we know when the bug will be fixed?

I think trigger needs to be a new element like: new CognitoTrigger so the dependson can be added

[Townsheriff]

I want to mention that, I'm passing user pool id as the env variable and it has the same error effect. This just makes things weird, that I need to pass userPoolId in the parameter store to utilise it in the lambda.

[Townsheriff]

Today I noticed that userPoolId is inside event object for lambda.

[KennethVrb]

any further news on this? i'm havinga similar issue where a userpool depends on a lambda as it trigger for CustomMessage but the lambda needs the userpoolid as an environment variable

[Townsheriff]

any further news on this? i'm havinga similar issue where a userpool depends on a lambda as it trigger for CustomMessage but the lambda needs the userpoolid as an environment variable

Lambda receives userPoolId in the event argument.

[Selimmo]

I had the same problem and i ended up doing something like this

const fn = new Function(stack, 'fn', {
  code: Code.fromInline('foo'),
  runtime: Runtime.NODEJS_12_X,
  handler: 'index.handler',
});

const userpool = new UserPool(stack, 'pool', {
  lambdaTriggers: {
    userMigration: fn
  }
}); 

const cognitoAdminPolicyStatement  = new PolicyStatement({
   effect: Effect.ALLOW,
   actions: 'cognito-idp:*',
   resources: [
       `arn:aws:cognito-idp:${region}:${account}:userpool/${userPoolId}`
   ]
 });

const lambdaRole = Role.fromRoleArn(this, 'lambdaRole', fn.role!.roleArn);

lambdaRole.addToPrincipalPolicy(cognitoAdminPolicyStatement);

Basically the trick is retrieve the role as if it was created in another stack. (i know and i don't like it as well) but it seems to do the trick for now.

[MiguelNiblock]

Today I noticed that userPoolId is inside event object for lambda.

This saved me. I also got this error when trying to pass the pool.userPoolId to the lambda environment. But now I don't need to do that because it is included in the event, because it's a cognito post confirmation trigger. Thanks!

[shawnmclean]

I'm running into this exact circular dependency but from CloudFormation. How can I implement this delayed adding of the policy to the lambda role?

[Torsitano]

@shawnmclean Not sure if you're still running into that issue, but normally with regular CloudFormation you'd use the AWS::IAM::ManagedPolicy or AWS::IAM::Policy resources to get around a circular dependency between a resource and an IAM Role.

If you have a resource that needs a policy based on the Role, but the Role also needs a policy specifying the resource, the chain will go: AWS::IAM::Role AWS::Other::Resource AWS::IAM::ManagedPolicy

Each depends on the one prior, but since the Managed Policy is created at a later point and attached to the IAM Role, it is not circular.

[teuteuguy]

I have the same issue with providing the lambda function with the list of app clientIds as environment variables upon creation.

Has this been looked into ?

[BartekCK]

Problem still exist, but workaround with attachInlinePolicy helps in some cases.

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[jamesleech]

I have the same issue with providing the lambda function with the list of app clientIds as environment variables upon creation.

Has this been looked into ?

I have two app clients, and want to do different things in cognito triggers based on the app client the user is coming in via... think mobile app client vs web.

if event.callerContext.callerContext.cliendId = appClientId { do stuff } else if event.callerContext.callerContext.cliendId = webClientId { do different stuff. }

I'm getting circular reference when creating cognito, added a second client, and then trying to bind the Ids of the clients into params and/or env vars.

Is there a workaround for this?

cognito depends on the trigger lambdas trigger lambdas depend on cognito to be created to give me ids

I really don't want to use ssm at trigger runtime to get the ids.

[KomaGR]

I am facing a similar problem because I'm trying to pass the userPoolId in the Lambda trigger. Is there a way to know the userPoolId without passing it as an env var?

        const postConfirmationLambda = new lambdaNodejs.NodejsFunction(this, 'postConfirmationLambda', {
            entry: 'lambda-functions/user-pool-trigger/post-confirmation.ts',
            environment: {
                "USER_POOL": cognitoUserPool.userPoolId, /* This causes a circular dependency while deploying */
            }
        });

[ignaciolarranaga]

Just to add to the discussion I resolved it using cloud trail events:

export function buildTestUsersHandlerFunction(
  scope: Construct,
  env: Environment,
  userPool: IUserPool
) {
  const lambda = new Function(scope, 'TestUsersHandler', {
    ...
  });

  userPool.grant(lambda, 'cognito-idp:AdminGetUser');
  userPool.grant(lambda, 'cognito-idp:AdminAddUserToGroup');

  addCognitoEventTarget(scope, env, lambda);
}

function addCognitoEventTarget(
  scope: Construct,
  env: Environment,
  lambda: IFunction
) {
  // WARNING: This function needs the Trail created by buildCloudTrailTrail to work
  const eventRule = Trail.onEvent(scope, 'CognitoSignUpUserEventRule', {
    target: new LambdaFunction(lambda),
  });

  eventRule.addEventPattern({
    source: ['aws.cognito-idp'],
    detailType: ['AWS API Call via CloudTrail'],
    detail: {
      eventSource: ['cognito-idp.amazonaws.com'],
      eventName: ['SignUp'],
    },
  });
}

This way each time an operation is made through the Cognito API I route an event to this lambda. Tried the other suggested approaches but couldn't get rid of the circular dependency.

[ALFmachine]

for me everything works smashingly until cognitoPool.addTrigger(trigger, this.handler) which causes the circular dep trail...

[Wegetal]

I'm facing a similar issue, I'm creating the lambdas after the UserPool and AppClients are created, I then use the app clients to populate a few env variables for the lambdas when creating them (I need a mapping so the event client id is not useful here), and then I just add them as triggers, so the issue is around the env variables, if I dont use the clients to populate it it works, otherwise just throws a circular reference

[flaxpanda]

this approach is the only way we have been able to solve for this currently

[viniciustrindade]

I am facing a similar problem because I'm trying to pass the userPoolId in the Lambda trigger. Is there a way to know the userPoolId without passing it as an env var?

        const postConfirmationLambda = new lambdaNodejs.NodejsFunction(this, 'postConfirmationLambda', {
            entry: 'lambda-functions/user-pool-trigger/post-confirmation.ts',
            environment: {
                "USER_POOL": cognitoUserPool.userPoolId, /* This causes a circular dependency while deploying */
            }
        });

You can use event.userPoolId inside of the lamba

[b-tin]

event.userPoolId

this save me to avoid the error when passing variable environment to lambda

[toddarmstrong]

I ran into this issue but regarding using a User Pool Id or User Pool Client Id as an environment variable for a Lambda function I was assigning as a trigger to the User Pool. My fix for this was to use addTrigger() on the User Pool after setting everything up and using lambda.Function.fromFunctionArn() to reference the function.

const userPool = new cognito.UserPool(this, "UserPool", {
  ...
});

const client = new cognito.UserPoolClient(this, "UserPoolClient", {
  userPool,
  ...
});

const lambdaFunctionName = "function-name";
const lambdaFunction = new lambda.Function(this, "LambdaFunction", {
  functionName: lambdaFunctionName,
  environment: {
    USER_POOL_CLIENT_ID: client.userPoolClientId,
  },
  ...
});

userPool.addTrigger(
  cognito.UserPoolOperation.PRE_SIGN_UP,
  lambda.Function.fromFunctionArn(
    this,
    `PreSignUpLambdaFunction`,
    `arn:aws:lambda:${props.env.region}:${props.env.account}:function:${lambdaFunctionName}`
  )
);