How can I get a map using flatten in Terraform?

Question

I have this variable:

applications = {
  "app-name" = {
    more_stuff = "x"
    environments = ["dev", "stg"]
  }
  "workload" = {
    random_thing = "y"
    environments = ["dev"]
  }
}

I want to create this map from it:

application_envs = {
  "app-name-dev" = { more_stuff = "x" }
  "app-name-stg" = { more_stuff = "x" }
  "workload-dev" = { random_thing = "y" }
}

I've tried using flatten but I didn't have any success:

application_envs = flatten([
  for application_key, application in var.applications : [
    for env in application.environments : [
      {"${application_key}-${env}" = workspace}
    ]
  ]
])

The problem is that it creates a list of objects:

result = [
  { "app-name-dev" = { ... } },
  { "app-name-stg" = { ... } },
  ...
]

How can I achieve the desired result?

Matthew Schuchard · Accepted Answer · 2022-12-28 21:06:10Z

3

You are headed in the correct direction, but for this kind of data transformation the algorithm requires two steps. Your first step is completely correct, but now you need the second step:

result = { for app_env in application_envs : keys(app_env)[0] => values(app_env)[0] }

This transforms the list(object) by iteratively mapping the key of each object element to the value of each object element. Testing the output produces:

result = {
  app-name-dev = {
    more_stuff = "x"
  }
  app-name-stg = {
    more_stuff = "x"
  }
}

as desired. Since the namespaces of the variables have been omitted from the question, I have likewise omitted them from the answer, but you may need to re-add them yourself when converting between the question code and the actual code.

answered Dec 28, 2022 at 21:06

Matthew Schuchard

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