[BUG] opensearch_index number_of_replicas is optional but breaks on subsequent applies if unset

[arichtman-srt]

What is the bug?

Terraform tries to set the number of replicas back to null, which will never work.

How can one reproduce the bug?

1. Create a resource block of opensearch_index type and set the only required property, name
2. Apply the Terraform, the index should now be created
3. Terraform plan, it should show a diff on the property number_of_replicas
4. Terraform apply, it will fail trying to set number_of_replicas to null

What is the expected behavior?

Either:
A) It's possible to set replica count to nothing, in which case Terraform does so
B) Number of replicas property should be mandatory

What is your host/environment?

$ uname -a && terraform -version

Darwin bne-nb-ariel 22.5.0 Darwin Kernel Version 22.5.0: Thu Jun  8 22:21:34 PDT 2023; root:xnu-8796.121.3~7/RELEASE_ARM64_T8112 arm64 arm Darwin
Terraform v1.3.9
on darwin_arm64
+ provider registry.terraform.io/hashicorp/aws v5.7.0
+ provider registry.terraform.io/opensearch-project/opensearch v1.0.0

Your version of Terraform is out of date! The latest version
is 1.5.2. You can update by downloading from https://www.terraform.io/downloads.html

Do you have any screenshots?

Do you have any additional context?

Technically it's correct that replica count isn't required to create an index. But I'm no software philosopher.

[peterzhuamazon]

[Triage] Adding @prudhvigodithi to take a look on this.
Thanks.

[prudhvigodithi]

Hey @arichtman-srt can you please test with the latest release? https://registry.terraform.io/providers/opensearch-project/opensearch/2.0.0-beta.1
Thank you

[rlanore]

Tested today with 2.1.0 and no working with this example:

Example from doc opensearch_index_template resource are not working. I had to update the json.

# Create an index template
resource "opensearch_index_template" "logs_1" {
  name = "logs_1"
  body = <<EOF
{
  "index_patterns": [ "logs*" ],
  "template": {
    "settings": {
      "index": {
        "number_of_shards": "1",
        "number_of_replicas": "0",
        "refresh_interval": "5s"
      }
    }
  }
}
EOF
}

# Create a simple index
resource "opensearch_index" "logs-01" {
  name               = "logs-01"
}

as output

Terraform will perform the following actions:

  # opensearch_index.logs-01 will be updated in-place
  ~ resource "opensearch_index" "logs-01" {
        id                 = "logs-01"
        name               = "logs-01"
      - number_of_replicas = "0" -> null
      - refresh_interval   = "5s" -> null
        # (2 unchanged attributes hidden)
    }
Plan: 0 to add, 1 to change, 0 to destroy.
opensearch_index.logs-01: Modifying... [id=logs-01]
╷
│ Error: elastic: Error 400 (Bad Request): failed to parse setting [index.refresh_interval] with value [] as a time value: unit is missing or unrecognized [type=illegal_argument_exception]
│
│   with opensearch_index.logs-01,
│   on main.tf line 50, in resource "opensearch_index" "logs-01":
│   50: resource "opensearch_index" "logs-01" {

[rlanore]

As a workaround

# Create a simple index
resource "opensearch_index" "logs-01" {
  name               = "logs-01"
  lifecycle {
    ignore_changes = [
      number_of_replicas,
      refresh_interval
    ]
  }
}