Example: Using devcontainer.json to influence a Coder (Terraform) template

[bpmct]

Note

I'm not sure how realistic this is, or whether it should be out of scope envbuilder as it's likely a Terraform provider/Coder feature. However, this is a somewhat common use case. It may not be a good fit for envbuilder v1.0 but worth discussing

Since envbuilder is a container image, it cannot influence the underlying infrastructure it can be provisioned on. However some Dev Container features do have support for additional infrastructure layers. Can we provide an example of how a Coder template can read a devcontainer.json and then influence the template? We have some customers doing this today with a custom coder.yaml

Example: Kubernetes Volume Mounts

# The jank approach (pseudocode, untested)
data "http" "devcontainer_contents" {
  url = "${var.git_repo}/${var.git_branch}/.devcontainer/devcontainer.json"

  request_headers = {
    Accept = "application/vnd.github.v3.raw"
  }
}

locals {
  # Attempt to parse mounts from the devcontainer JSON
  parsed_mounts = try(jsondecode(data.http.devcontainer_contents.body).mounts, [])
  
  # Use a default mount if no mounts are specified or if the mounts key doesn't exist
  mounts = length(local.parsed_mounts) > 0 ? local.parsed_mounts : ["source=workspace,target=/workspaces,type=volume"]
  
  # Extracting target paths for PVC creation and Pod mounts
  target_paths = [for m in local.mounts : split(",", m)[1]]
  target_path_names = { for m in local.target_paths : split("=", m)[1] => split("=", m)[1] }
}

resource "kubernetes_persistent_volume_claim" "pvc" {
  for_each = local.target_path_names

  metadata {
    name = "pvc-${replace(each.value, "/", "-")}"
  }

  spec {
    access_modes = ["ReadWriteOnce"]
    resources {
      requests = {
        storage = "1Gi"
      }
    }
  }
}

resource "kubernetes_pod" "example" {
  metadata {
    name = "example-pod"
  }

  spec {
    container {
      image = "nginx"
      name  = "example"

      volume_mount {
        for_each = local.target_path_names
        name     = "pvc-${replace(each.value, "/", "-")}"
        mount_path = each.value
      }
    }

    volume {
      for_each = local.target_path_names
      name = "pvc-${replace(each.value, "/", "-")}"

      persistent_volume_claim {
        claim_name = "pvc-${replace(each.value, "/", "-")}"
      }
    }
  }
}
 image = "nginx"
      name  = "example"

      volume_mount {
        for_each = local.target_path_names
        name     = "pvc-${replace(each.value, "/", "-")}"
        mount_path = each.value
      }
    }

    volume {
      for_each = local.target_path_names
      name = "pvc-${replace(each.value, "/", "-")}"

      persistent_volume_claim {
        claim_name = "pvc-${replace(each.value, "/", "-")}"
      }
    }
  }
}

Option 2: TF Provider

The Coder server reads the devcontainer.json and passes data via a Terraform data source. This is related to coder/coder#8462.

Option 3: envbuilder + docker on a VM

If envbuilder runs on a VM, it could realistically do significantly more such as create Docker volumes as well as run a container.