Add a way to write properties from resources to a file in S3

🚀 feature request

Some way of writing some of the values from resources to a file in S3.

Eg, something like:

const myBucket = new s3.Bucket(this, 'MyBucket');
new s3deploy.BucketDeployment(this, 'MyConfigFile', {
    source: s3deploy.Source.fromString(`{"thisBucketArn": "${myBucket.bucketArn}"}`),
    destinationBucket: myBucket,
    destinationKeyPrefix: 'config.json',
});

should deploy the bucket, then write the ARN of the bucket to the json file in the bucket at config.json.

I suspect there’s a way to do this already by abusing assets sufficiently, but I haven’t been able to make it work. The closest I can get is to write the variables into the source for a lambda and access them using API gateway, but that seems silly.

[plumdog]

I did manage to handle this using the rather marvellous AwsCustomResource in @aws-cdk/custom-resources:

const config = {
  myBucketArn = myBucket.bucketArn,
};
new customResources.AwsCustomResource(this, 'WriteS3ConfigFile', {
  onUpdate: {
    service: 'S3',
    action: 'putObject',
    parameters: {
      Body: JSON.stringify(config),
      Bucket: myBucket.bucketName,
      Key: 'config.json',
    },
    physicalResourceId: Date.now().toString(),  // always write this file
  },
  // we need this because we're not doing conventional resource creation
  policyStatements: [
    new iam.PolicyStatement({
       actions: ['s3:PutObject'],
       resources: [`${myBucket.bucketArn}/config.json`],
    }),
  ],
});

Whether the right thing to do is: a) bundling this up a reusable construct b) writing something bespoke (I don’t know enough about the internal to know what that would be) c) documenting this a workaround d) not bothering with either

I’m not sure. I suppose if this is functionality that lots of people might require, then a or b. If only a few, then c. If very very few (or just me), then d.

[jagregory]

+1 I think the s3 deployment would be a good place for this too. I’m uploading a bunch of files with a deployment, but I’d like one of them to be templated with information from the deployment (think environment name, S3 bucket URL etc).