HCS-1760: Add Consul versions data source

[alexmunda]

Based off the hcs_consul_versions data source, we can allows users to explicitly set their Consul cluster version to the latest recommended Consul version that HCP supports. This means that any time the recommended HCP Consul version changes, someone utilizing the recommended field of the consul_versions data source will be prompted to upgrade their cluster the next time they run terraform plan:

❯ terraform plan
hcp_hvn.example_hvn: Refreshing state... 
hcp_consul_cluster.example_consul_cluster: Refreshing state... 

An execution plan has been generated and is shown below.
Resource actions are indicated with the following symbols:
  ~ update in-place

Terraform will perform the following actions:

  # hcp_consul_cluster.example_consul_cluster will be updated in-place
  ~ resource "hcp_consul_cluster" "example_consul_cluster" {
        id                            = "/project/XXX/hashicorp.consul.cluster/hcp-tf-example-consul-cluster"
      ~ min_consul_version            = "v1.9.2" -> "v1.9.3"
        # (19 unchanged attributes hidden)
    }

Plan: 0 to add, 1 to change, 0 to destroy.

This data source also informs users of the Consul versions that HCP supports, in the case where they are looking to use a specific Consul version.

If HCP offers preview versions of Consul in the future, users would be able to discover and set min_consul_version of their cluster using this data source.

❯ tf show
# data.hcp_consul_versions.versions:
data "hcp_consul_versions" "versions" {
    available   = [
        "v1.9.3",
        "v1.9.2",
        "v1.9.1",
        "v1.9.0",
        "v1.8.8",
        "v1.8.7",
        "v1.8.6",
        "v1.8.4",
        "v1.8.0",
    ]
    id          = "recommended/v1.9.3/available_len/9/preview_len/0"
    preview     = []
    recommended = "v1.9.3"
}

Usage:

data "hcp_consul_versions" "versions" {}

resource "hcp_consul_cluster" "example_consul_cluster" {
  hvn_id             = hcp_hvn.example_hvn.hvn_id
  cluster_id         = "hcp-tf-example-consul-cluster"
  tier               = "development"
  min_consul_version = data.hcp_consul_versions.versions.recommended
}

[mkeeler]

Two things.

First is should we expose preview versions in the provider before we support them in HCP itself? If we wanted to call them something other than preview in the future once we went down the path of implementing them then it would potentially be a breaking change to the provider.

Secondly the doc comment I pointed out doesn't match the func name. However the name in the comment is referenced from new code so I am not too sure whats going on here.

[alexmunda]

First is should we expose preview versions in the provider before we support them in HCP itself? If we wanted to call them something other than preview in the future once we went down the path of implementing them then it would potentially be a breaking change to the provider.

Great point @mkeeler. Fortunately this implementation is tied to the VersionStatus enum in the 2020-08-26 version of the consul-service API. If down the road that enum is changed, it would require a new consul-service API version to be created, the 2020-08-26 version would still function as expected, and we could safely update the data source implementation to the new API version's enum without breaking existing functionality.

[roaks3]

LGTM, my comment on the id used here should not be blocking

[alexmunda]

data "hcp_consul_versions" "versions" {
    available   = [
        "v1.9.3",
        "v1.9.2",
        "v1.9.1",
        "v1.9.0",
        "v1.8.8",
        "v1.8.7",
        "v1.8.6",
        "v1.8.4",
        "v1.8.0",
    ]
    id          = "16fe24158cef6090063cae717b555142"
    preview     = []
    recommended = "v1.9.3"
}

[roaks3]

LGTM, just had one comment that might make the ids more robust

[roaks3]

Would it be weird to prepend this string with something like recommended: (and same for line 61)? It might be overkill, but I think there's an edge case where eg. v1.9.0, v1.8.6, v1.8.4 would be produced by two configurations: no recommended version, and v1.9.0 recommended version.

[alexmunda]

I can definitely get behind adding it for this line. On 61 since there would only be 1 version returned (the recommended one) it seems like overkill 🤷