How to add S3 BucketPolicy with AWS CDK?

Question

I wanna translate this CloudFormation piece into CDK:

Type: AWS::S3::BucketPolicy
Properties:
  Bucket:
    Ref: S3BucketImageUploadBuffer
  PolicyDocument:
    Version: "2012-10-17"
    Statement:
      Action:
        - s3:PutObject
        - s3:PutObjectAcl
      Effect: Allow
      Resource:
        - ...

Looking at the documentation here, I don't see a way to provide the policy document itself.

Answer 1

This is an example from a working CDK-Stack:

   artifactBucket.addToResourcePolicy(
      new PolicyStatement({
        resources: [
          this.pipeline.artifactBucket.arnForObjects("*"), 
          this.pipeline.artifactBucket.bucketArn],
        ],
        actions: ["s3:List*", "s3:Get*"],
        principals: [new ArnPrincipal(this.deploymentRole.roleArn)]
      })
    );

Answer 2

Building on @Thomas Wagner's answer, this is how I did this. I was trying to limit the bucket to a given IP range:

import * as cdk from '@aws-cdk/core';
import * as s3 from '@aws-cdk/aws-s3';
import * as s3Deployment from '@aws-cdk/aws-s3-deployment';
import * as iam from '@aws-cdk/aws-iam';

export class StaticSiteStack extends cdk.Stack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    // Bucket where frontend site goes.
    const mySiteBucket = new s3.Bucket(this, 'mySiteBucket', {
      websiteIndexDocument: "index.html"
    });

    let ipLimitPolicy = new iam.PolicyStatement({
      actions: ['s3:Get*', 's3:List*'],
      resources: [mySiteBucket.arnForObjects('*')],
      principals: [new iam.AnyPrincipal()]
    });
    ipLimitPolicy.addCondition('IpAddress', {
      "aws:SourceIp": ['1.2.3.4/22']
    });
    // Allow connections from my CIDR
    mySiteBucket.addToResourcePolicy(ipLimitPolicy);


    // Deploy assets
    const mySiteDeploy = new s3Deployment.BucketDeployment(this, 'deployAdminSite', {
      sources: [s3Deployment.Source.asset("./mysite")],
      destinationBucket: mySiteBucket
    });

  }
}

I was able to use the s3.arnForObjects() and iam.AnyPrincipal() helper functions rather than specifying ARNs or Principals directly.

The assets I want to deploy to the bucket are kept in the root of my project directory in a directory called mysite, and then referenced via a call to s3Deployment.BucketDeployment. This can be any directory your build process has access to, of course.

Answer 3

The CDK does this a little differently. I believe you are supposed to use bucket.addToResourcePolicy, as documented here.

Answer 4

As per the original question, then the answer from @thomas-wagner is the way to go.

If anyone comes here looking for how to create the bucket policy for a CloudFront Distribution without creating a dependency on a bucket then you need to use the L1 construct CfnBucketPolicy (rough C# example below):

    IOriginAccessIdentity originAccessIdentity = new OriginAccessIdentity(this, "origin-access-identity", new OriginAccessIdentityProps
    {
        Comment = "Origin Access Identity",
    });

    PolicyStatement bucketAccessPolicy = new PolicyStatement(new PolicyStatementProps
    {
        Effect = Effect.ALLOW,
        Principals = new[]
        {
            originAccessIdentity.GrantPrincipal
        },
        Actions = new[]
        {
            "s3:GetObject",
        },
        Resources = new[]
        {
            Props.OriginBucket.ArnForObjects("*"),
        }
    });

    _ = new CfnBucketPolicy(this, $"bucket-policy", new CfnBucketPolicyProps
    {
        Bucket = Props.OriginBucket.BucketName,
        PolicyDocument = new PolicyDocument(new PolicyDocumentProps
        {
            Statements = new[]
            {
                bucketAccessPolicy,
            },
        }),
    });

Where Props.OriginBucket is an instance of IBucket (just a bucket).