From the examples it looks like Pulumi programs declare their infrastructure, causing it to be created. Doesn't that mean that the program will need privileged credentials? How do you make sure the app only has, say, read access to an S3 bucket it needs to listen to, and can't accidentally delete it? And how does that then allow it to declare the bucket?
> Doesn't that mean that the program will need privileged credentials?
Obviously whatever program is actually creating the cloud resources will need credentials to do so. However, they aren't part of the Pulumi program.
When you run `pulumi update` on your machine (or on a CI/CD server) Pulumi will pick up whatever ambient credentials are on the machine. (e.g. ~/.aws/credentials.) So if you to restrict the credentials used to update a particular Pulumi stack, you just need to swap out whatever the current credentials are. (e.g. an AWS_ACCESS_KEY_ID env var.)
> How do you make sure the app only has, say, read access to an S3 bucket it needs to listen to, and can't accidentally delete it? And how does that then allow it to declare the bucket?
There are a lot of good questions there, so let me show you a quick example:
This snippet will create a new AWS S3 bucket named "example.com-images". It also sets the default ACL for the bucket to "private". Nothing too surprising there.
If you wanted another resource to have read access to that bucket, you would need to configure AWS to grant access. The Pulumi programming model is about how you declare/describe/create resources, but not actually define policy for how they work. So when using AWS, you would potentially need to create an `aws.iam.Role` / `aws.iam.RolePolicyAttachment` object and hook them up. (Or, if using Azure or GCP, configure access using some other method.)
So in short, to configure what _cloud resources_ can read/write other _cloud resources_, it's a matter of how the cloud resource provider exposes that.
When it comes to matters like preventing you from accidentally deleting the resources when you run `pulumi update` on a program, there are a few features that can help you with that. You can mark a resource as `protected`, so that any update that would delete that resource would produce an error. (Until you update the program again, making that resource as not protected.) Also, the `aws.s3.Bucket` type has a `forceDelete` parameter, that does something very similar. Unless set to true, the Bucket object cannot be deleted. (Thereby preventing some accidental dataloss.)
Makes sense. That makes it sound like Pulumi only runs the infrastructure declarations when you run "pulumi update", and that those things don't run when your program runs. That's confusing to me, because your examples (like the thumbnailer) seems to have the program and the declarations in the same file.
Is Pulumi stateful, then? If you create resources with "pulumi update", change the declarations without updating, and run "pulumi destroy" or whatever, it will only delete the stuff you created in the first step? (That is what I would expect. I would also expect it to support a dry run mode with a diff showing what operations would be executed.) If so, where is this state stored?
> That makes it sound like Pulumi only runs the infrastructure declarations when you run "pulumi update", and that those things don't run when your program runs. That's confusing to me, because your examples (like the thumbnailer) seems to have the program and the declarations in the same file.
This is an optional way to do it, by combining the runtime code and infra code. The runtime code doesn't run when you deploy with "pulumi update," but it is packaged and sent to AWS.
> Is Pulumi stateful, then? If you create resources with "pulumi update", change the declarations without updating, and run "pulumi destroy" or whatever, it will only delete the stuff you created in the first step? (That is what I would expect. I would also expect it to support a dry run mode with a diff showing what operations would be executed.) If so, where is this state stored?
Yes, the state is stored on pulumi.com. The state is list of resource IDs that you provisioned. The Pulumi CLI does indeed have a dry run mode that shows a diff: whenever you run "pulumi update", it first shows a preview.
Yes, Pulumi does mutate resources in place, if the cloud provider supports it. For most resources, it will create a new one (such as a new ECS task), and wait for it to be ready before deleting the old one.
