Avoid triggering an update if Resource.Schema attribute changes in Terraform

Question

I'm trying to figure out if it is possible to prevent resource updates when one of the Resource.Schema attributes changes.

Essentially I'm building a provider that manages infrastructure. I've got a resource that updates firmware. Something like:

resource "redfish_simple_update" "update" {
    transfer_protocol = "HTTP"
    target_firmware_image = "/home/mikeletux/BIOS_FXC54_WN64_1.15.0.EXE"
}

As you can see, target_firmware_image does refer to the full path of my firmware package. I want to be able to change directories without triggering an update. I.e. changing above target_firmware_image by /home/mikeletux/Downloads/BIOS_FXC54_WN64_1.15.0.EXE for instance.

I don't know if this is possible. If done my own research and I found the CustomDiff functions to be added to the schema, but I think that thing doesn't match my scenario.

Do you think of something else I could do?

Thanks!

Answer 1

Just posting here how I finally did it.

To avoid triggering an update when the path changes but not the filename, I've found out that DiffSuppressFunc function becomes very handy here:

"target_firmware_image": {
        Type:     schema.TypeString,
        Required: true,
        Description: "Target firmware image used for firmware update on the redfish instance. " +
            "Make sure you place your firmware packages in the same folder as the module and set it as follows: \"${path.module}/BIOS_FXC54_WN64_1.15.0.EXE\"",
        // DiffSuppressFunc will allow moving fw packages through the filesystem without triggering an update if so.
        // At the moment it uses filename to see if they're the same. We need to strengthen that by somehow using hashing
        DiffSuppressFunc: func(k, old, new string, d *schema.ResourceData) bool {
            if filepath.Base(old) == filepath.Base(new) {
                return true
            }
            return false
        },
    }

By checking old and new value using filepath.Base(), I can figure out if filename is the same, no matter what path the file is placed in.

I'd like to improve that behavior in the future by implementing file hashing, so even the filename doesn't matter, but that's something I'll leave for a new version.

Thanks!