feature request: formation batch updates

[dentarg]

There's support in the Platform API to do Formation Batch Update and I can see that it is implemented in the Go client.

Could be useful if you have a complex setup, right?

[mars]

Batch API updates are not generally applicable to Terraform providers, because in Terraform each resource is managed on its own, using self-contained lifecycle logic and API calls. Terraform does not provide a strategy for merging resource updates together into composite API calls.

[dentarg]

The reason I was asking for this is that I want to avoid this

╷
│ Error: Patch "https://api.heroku.com/apps/0c0b1941-7aef-48b3-b52e-863051aa642f/formation/worker": Cannot use the following dyno types in the same app: Basic and Standard-1X
│
│   with module.worker.heroku_formation.formation["0"],
│   on create_app/create_app.tf line 34, in resource "heroku_formation" "formation":
│   34: resource "heroku_formation" "formation" {
│
╵

It happens because https://github.com/heroku/heroku-buildpack-ruby automatically adds a Basic web dyno to my app even when I haven't asked for it (because I've declared a certain dependency in my project).

I have a repro of what I'm doing at https://github.com/dentarg/gists/tree/2f3f3e5ed324aebd262ae2cd67fff1280dacb1bf/gists/terraform-heroku_formation

I would need to make one heroku_formation to scale down web and after that scale my worker dyno. Having the batch formation would be much easier way of doing that.

[mars]

Thanks for the additional explanation @dentarg. It's definitely easier to respond to issues when they have details like this.

Restating why this issue is closed: Terraform does not support batching of API calls between/across resources.

To solve this following your suggestion, a whole new heroku_formations (plural) resource would need to be implemented, to use that batch API from a single resource, enabling something like this:

resource "heroku_formations" "example" {
  app_id = heroku_app.example.id

  formation {
    type     = "web"
    size     = "standard-1x"
    quantity = 0
  }

  formation {
    type     = "worker"
    size     = "standard-1x"
    quantity = 1
  }
}

As a maintainer, I'm open to such an addition, if it actually solves a problem… but I really believe this problem is already solvable using the current provider.

would need to make one heroku_formation to scale down web and after that scale my worker dyno

Terraform is designed to string together resource dependencies like this. It will likely work better than creating/implementing a new heroku_formations resource to batch the formation changes. Example:

resource "heroku_formation" "example_web_down" {
  app_id   = heroku_app.example.id
  type     = "web"
  size     = "standard-1x"
  quantity = 0
}

resource "heroku_formation" "example_worker_up" {
  app_id   = heroku_app.example.id
  type     = "worker"
  size     = "standard-1x"
  quantity = 1

  depends_on = [
    heroku_formation.example_web_down
  ]
}

If you find that heroku_formation resources cannot solve this problem, and you validate that formation batch updates do solve it, then please revisit this issue with us.

[dentarg]

Yeah, I know I can use depends_on, I just haven't structured my code that way right now. (from the repro I linked)

I thought I could specify the complete formation of an app like this

  formation = [
    {
      quantity = 0
      size = "Standard-1X"
      type = "web"
    },
    {
      quantity = 1
      size = "Standard-1X"
      type = "worker"
    },
  ]

and then iterate over that with heroku_formation like this

resource "heroku_formation" "formation" {
  for_each   = {for i, v in var.formation:  i => v}

  app_id     = heroku_app.app.id
  quantity   = each.value.quantity
  size       = each.value.size
  type       = each.value.type
  depends_on = [heroku_build.build]
}

but the auto-added Basic web dyno made that not work reliable

Hopefully https://github.com/heroku/heroku-buildpack-ruby can be changed to be less magic if the user wants, talking to @schneems about it