Terraform iterate over nested data

Question

I'm trying to create New Relic's service-level objects based on a yaml config file that provides the relevant configuration. My yaml configuration:

slo:
  targets:
  - first_slo:
    name: "My First SLO"
    endpoints:
      - path: /api/method1
        method: GET
      - path: /api/method2
        method: PUT
    objectives:
      availability:
        threshold: 99.9
  - first_slo:
    name: "My Second SLO"
    endpoints:
      - path: /api/method12
        method: GET
      - path: /api/method23
        method: PUT
    objectives:
      availability:
        threshold: 99.99

I want to iterate over this example configuration to build the object, but I'm struggling to form the right NRQL query using a nested iteration.

My terraform file:

resource "newrelic_service_level" "availability" {
  for_each  = var.config.slo.targets
  guid = var.guid
  name = "${each.value.name} - Availability"
  description = "Proportion of requests that are served successfully."

  events {
    account_id = var.account_id
    valid_events {
      from = "Transaction"
      where = "transactionType='Web' AND entityGuid = '${var.guid}' AND (OR_CONDITION_BETWEEN_ALL_THE_METHODS_AND_URIS)"
    }
    bad_events {
      from = "Transaction"
      where = "transactionType= 'Web' AND entityGuid = '${var.guid}' AND numeric(response.status) >= 500 AND (OR_CONDITION_BETWEEN_ALL_THE_METHODS_AND_URIS)"
    }
  }

  objective {
    target = each.value.objectives.availability.threshold
    time_window {
      rolling {
        count = 7
        unit = "DAY"
      }
    }
  }
}

So basically what I'm trying to do here, is create a service level with an NRQL query that filters only for the specific combination of URI and method that are relevant for this specific target - the URI and methods that I have in my config file.

So for the first SLO, OR_CONDITION_BETWEEN_ALL_THE_METHODS_AND_URIS should translate to something like this: (request.uri = '/api/method1' AND request.method = 'GET') OR (request.uri = '/api/method2' AND request.method = 'PUT')

My current solution would be to build the query manually and add it to the configurations for each SLO, but it is not readable and hard to maintain.

I would highly appreciate any suggestions on how to build the query dynamically.

Answer 1

You can certainly build that query with Terraform. Here's a wee .tf file that shows how you could do it:

locals {
  config = yamldecode(file("${path.root}/vars.yaml"))
  parsed = [for d in local.config.slo.targets : {
    name : d["name"]
    condition : join(" OR ", [for e in d["endpoints"] : "(request.uri = '${e["path"]}' AND request.method = '${e["method"]}')"])
  }]
}

output "parsed" {
  value = local.parsed
}

This expects your yaml file to be sitting next to it with name vars.yaml, and produces:

$ terraform plan

Changes to Outputs:
  + parsed = [
      + {
          + condition = "(request.uri = '/api/method1' AND request.method = 'GET') OR (request.uri = '/api/method2' AND request.method = 'PUT')"
          + name      = "My First SLO"
        },
      + {
          + condition = "(request.uri = '/api/method12' AND request.method = 'GET') OR (request.uri = '/api/method23' AND request.method = 'PUT')"
          + name      = "My Second SLO"
        },
    ]

For your module, you can just use the join(...) part in place of OR_CONDITION_BETWEEN_ALL_THE_METHODS_AND_URIS. Having it repeated should be fine (as long as you document it, naturally), but if you don't like the big long line, you can create a sub-module to encapsulate it. Or you could build the query string in a pre-processing locals block, possibly using the merge function to just add the query string alongside the rest of each target's config.