Free tool

API Gateway integration role policy generator

Pick the services your API Gateway calls and get the integration role it needs — scoped to the right ARNs, with the reason behind every action.

1. Which thing needs the role?

The compute that makes the calls. It assumes the role; everything else is a resource the role points at.

Principal

Changing this opens that principal’s own page.

2. What does it call?

Only connections the knowledge base records IAM requirements for. Tick what your API Gateway actually talks to.

DynamoDBDirect AWS service integration — API Gateway maps HTTP methods straight onto DynamoDB actions (GetItem/PutItem/Query/etc.) with no Lambda in between, for a simple CRUD passthrough
Step FunctionsDirect AWS service integration — an API method starts a Step Functions execution (StartExecution for a Standard workflow, or StartSyncExecution for an Express workflow when the caller needs the result back synchronously), turning an HTTP request into a workflow run with no Lambda in between

3. Fill in your account (optional)

Leave these blank and the ARNs keep visible placeholders, so a half-finished policy fails instead of quietly granting more than you meant.

Region

Account ID

Role name

Your role

Nothing selected yet, so the role below can be assumed but grants nothing. Tick a service above.

identity-policy.json

{
  "Version": "2012-10-17",
  "Statement": []
}

trust-policy.json

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "APIGatewayAssumeRole",
      "Effect": "Allow",
      "Principal": {
        "Service": "apigateway.amazonaws.com"
      },
      "Action": "sts:AssumeRole"
    }
  ]
}

Before you apply this

These are the actions this integration typically needs — not a least-privilege proof. After you deploy, narrow the policy with IAM Access Analyzer, which generates one from the calls the principal actually made.
No permissions were generated. The role below can be assumed but grants nothing — pick at least one service this principal calls.

Worth knowing about a API Gateway integration role

API Gateway calls the backend service with this role, not with the caller's credentials. (Knowledge base, API Gateway → DynamoDB.)
This is not the account-level CloudWatch Logs role API Gateway uses for access logging — that one is configured once per account and is a different role.
The trust policy lets any apigateway.amazonaws.com resource in any account assume this role. AWS recommends narrowing it with an aws:SourceArn (and aws:SourceAccount) condition naming the specific resource that may assume it — add that once you know the ARN.

Grounded in the same data that validates diagrams

Design Beaver models AWS connections so it can tell you when a diagram is wrong. Part of that model is which IAM actions each integration needs and why — researched against AWS documentation, not inferred. This tool reads that data directly, which is why it can explain every statement instead of just emitting one.

It also means the tool knows what it doesn’t know. A connection the knowledge base has no IAM data for is skipped and named, never filled in with a plausible guess. Where an action comes from somewhere other than the knowledge base, it is labelled.

What a API Gateway integration role can be scoped to

API Gateway assumes this role through the apigateway.amazonaws.com service principal. These are the 2 connections the knowledge base records IAM requirements for:

API Gateway → DynamoDB

Direct AWS service integration — API Gateway maps HTTP methods straight onto DynamoDB actions (GetItem/PutItem/Query/etc.) with no Lambda in between, for a simple CRUD passthrough

dynamodb:GetItemdynamodb:PutItemdynamodb:Querydynamodb:UpdateItemdynamodb:DeleteItem

Attach an IAM role to the integration granting the specific DynamoDB actions the API needs — API Gateway calls DynamoDB with that role, not the caller's credentials

Write request/response mapping templates (VTL) to translate between the HTTP request and the DynamoDB API shape — there's no automatic proxy for service integrations the way there is for Lambda

API Gateway → Step Functions

Direct AWS service integration — an API method starts a Step Functions execution (StartExecution for a Standard workflow, or StartSyncExecution for an Express workflow when the caller needs the result back synchronously), turning an HTTP request into a workflow run with no Lambda in between

states:StartExecutionstates:StartSyncExecution

Attach an IAM role to the integration granting states:StartExecution (or states:StartSyncExecution) on the target state machine — API Gateway starts the workflow with that role, not the caller's credentials

Write request/response mapping templates (VTL) to translate the HTTP request into the StartExecution input and shape the response — as with any non-proxy service integration, there's no automatic passthrough

More on API Gateway in Design Beaver →

Generate a role for something else

Questions

Where do the actions come from?

From Design Beaver's AWS knowledge base — the same data its validation engine uses to check architecture diagrams. Each connection between two services records the IAM actions that integration needs and the reason it needs them, researched against AWS documentation. Nothing is generated by a model, and the tool refuses to guess: a service pair the knowledge base has no IAM data for is skipped and reported rather than invented.

Is this a least-privilege policy?

No, and it says so on every policy it generates. These are the actions the integration typically needs — a sound starting point, not proof of minimum access. After you deploy, narrow it with IAM Access Analyzer, which generates a policy from the calls the principal actually made. That is the only way to get a genuinely least-privilege result.

How is this different from the other IAM policy generators?

Most of them start from the action catalogue: search 20,000 actions across 400 services and pick the ones you want, which assumes you already know the answer. This one starts from the architecture — this Lambda calls DynamoDB and SQS — and works out the actions from there. It also scopes each statement to the right ARN, so s3:ListBucket lands on the bucket while s3:GetObject lands on the objects inside it.

Does anything I type leave my browser?

No. The generator runs entirely client-side. Bucket names, table names, account IDs and ARNs are never sent anywhere, and there is no signup.

Why are there two policies?

AWS needs both. The trust policy says who may assume the role — the service principal, like lambda.amazonaws.com. The identity policy says what the role may then do. A role with permissions but no trust policy cannot be assumed by anything, and a role with trust but no permissions can be assumed but does nothing.

Draw it instead, and the role attaches itself

Design Beaver knows which connections need a role because it checks them as you draw. Drop an IAM Role node onto a function and the warnings it resolves disappear. Free, in your browser — sign in with Google or GitHub to save your work.

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