No method to ignore changes in DynamoDB GSI

[hashibot]

This issue was originally opened by @cypai as hashicorp/terraform#13393. It was migrated here as part of the provider split. The original body of the issue is below.

---

Terraform Version

$ terraform -v
Terraform v0.8.8

Affected Resource(s)

• aws_dynamodb_table

Terraform Configuration Files

resource "aws_dynamodb_table" "FooBar" {
    name = "FooBar"
    read_capacity = 10
    write_capacity = 10
    hash_key = "foo-id"
    attribute {
        name = "foo-id"
        type = "S"
    }
    attribute {
        name = "bar-id"
        type = "N"
    }
    global_secondary_index {
        name = "bar-index"
        hash_key = "bar-id"
        read_capacity = 10
        write_capacity = 10
        projection_type = "ALL"
    }
    lifecycle {
        ignore_changes = ["read_capacity", "write_capacity"]
    }
}

References

• provider/aws: Don't always update DynamoDB read/write capacity terraform#5617

We would like to ignore read/write capacity for the GSI as well, but this configuration only ignores the read/write capacity of the top-level table. We weren't able to find any usable workaround, since we can't interpolate variables in the lifecycle, and wildcards are not supported.

Technically we could hardcode the randomly generated number like ignore_changes = ["global_secondary_index.3291674533.read_capacity"], but that's obviously a terrible solution since it would change every time we make a change.

[lra]

Ignoring the GSI with its ID is not a work-around, it does ignore the *_capacity but stiff diffs the whole GSI =(

[mcwqy9]

I've got some time this week to take a stab at this. I've done some golang in the past, but this would be my first contribution to this project. Can anyone suggest what might need to be done, at a high level? Would a good approach be to remove a GSI's capacity from the hash function that determines the number in "global_secondary_index.3291674533.read_capacity"? That would make that number stable through capacity changes, and allow an ignore to be hardcoded. Stab in the dark...

[playdoz]

I've been testing with the following and it seems to be working quite well, terraform will ignore the GSI read and write capacity (and unfortunately projection_type) changes but will pick up other changes like name, hash_key etc

lifecycle {
    ignore_changes = [
      "global_secondary_index",
      "read_capacity",
      "write_capacity",
    ]
  }

Not an ideal solution.

[mcwqy9]

Interesting. Let me try that on my end. What version of Terraform and what version of the AWS provider are you testing with?

…

On Nov 23, 2017 5:14 PM, "kimgov" ***@***.***> wrote: I've been testing with the following and it seems to be working quite well, terraform will ignore the GSI read and write capacity changes but will pick up other changes like name, hash_key etc lifecycle { ignore_changes = [ "global_secondary_index", "read_capacity", "write_capacity", ] } — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#671 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABV4JBMt-c1fQVEvg4hDVcWrtbo05m0Cks5s5gpvgaJpZM4N5B0u> .

[icybin]

Any update on this topic? What is the best terraform version to get out of this issue? I'm ussing 0.9.6 and I always see dynamodb things updated when I run terraform apply :(

[armanshan12]

Any updates on this issue?

[rsalmond]

So apparently the above PR fixed this issue, does anyone know how to reference the read/write capacity of a GSI in the ignore_changes field to make it happen?

[cypai]

The comments in the above PR say that it is just a refactoring, only that it makes it easier to address this issue. I don't think it's fixed yet.

[rsalmond]

@cypai ah you're right, thanks for pointing that out! I read the wrong issue number. I'm getting by with the workaround @kimgov provided above in the meantime.