AccessDeniedException: User is not authorized to perform: lambda:InvokeFunction

Question

I'm trying to invoke a lambda function from node.

var aws = require('aws-sdk');
var lambda = new aws.Lambda({
    accessKeyId: 'id',
    secretAccessKey: 'key',
    region: 'us-west-2'
});

lambda.invoke({
    FunctionName: 'test1',
    Payload: JSON.stringify({
        key1: 'Arjun',
        key2: 'kom',
        key3: 'ath'
    })
}, function(err, data) {
    if (err) console.log(err, err.stack);
    else     console.log(data);
});

The keys are for an IAM user. The user has AWSLambdaExecute and AWSLambdaBasicExecutionRole policies attached.

I get a permission error: AccessDeniedException: User: arn:aws:iam::1221321312:user/cli is not authorized to perform: lambda:InvokeFunction on resource: arn:aws:lambda:us-west-2:1221321312:function:test1

I read the docs and several blogs, but I'm unable to authorise this user to invoke the lambda function. How do get this user to invoke lambda?

Thanks.

Answer 1

The AWSLambdaExecute and AWSLambdaBasicExecutionRole do not provide the permissions that are being expressed in the error. Both of these managed policies are designed to be attached to your Lambda function itself, so it runs with these policies.

The error is saying the user under which the nodejs program is running does not have rights to start the Lambda function.

You need to give your IAM user the lambda:InvokeFunction permission:

1. Find your User in the IAM Management Console and click it.
2. On the "Permissions" tab, expand the "Inline Policies" section and click the "click here" link to add a policy".
3. Select a "Custom Policy".
4. Give your policy a name. It can be anything.
5. Put this policy in the Policy Document field.

Sample policy:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Stmt1464440182000",
            "Effect": "Allow",
            "Action": [
                "lambda:InvokeAsync",
                "lambda:InvokeFunction"
            ],
            "Resource": [
                "*"
            ]
        }
    ]
}

In this policy, I have included both methods to invoke lambda methods.

Update:

There is now also an IAM Managed Policy named AWSLambdaRole that you can assign to your IAM user or IAM role. This should give you the permissions you need.