Add context

[osterman]

what

• Support passing a label's context between label modules

why

• DRY

demo

module "label1" {
  source     = "../../"
  namespace  = "Namespace"
  stage      = "Stage"
  name       = "Name1"
  attributes = ["1", "2", "3", ""]
  tags       = {
    "SomeKey" = "SomeValue"
  }
}

module "label2" {
  source     = "../../"
  context    = "${module.label1.context}"
  name       = "Name2"
}

todo

• figure out how to inherit extra tags from var.tags <--- need help

[osterman]

This is working and produces the following output. I just don't know how to inherit the additional tags from the parent's context.

Outputs:

label1_attributes = 1-2-3
label1_context = {
  attributes = 1-2-3
  delimiter = -
  name = name1
  namespace = namespace
  stage = stage
  tags = map[SomeKey:SomeValue Name:namespace-stage-name1-1-2-3 Namespace:namespace Stage:stage]
}
label1_id = namespace-stage-name1-1-2-3
label1_name = name1
label1_namespace = namespace
label1_stage = stage
label1_tags = {
  Name = namespace-stage-name1-1-2-3
  Namespace = namespace
  SomeKey = SomeValue
  Stage = stage
}
label2_attributes = 1-2-3
label2_context = {
  attributes = 1-2-3
  delimiter = -
  name = name2
  namespace = namespace
  stage = stage
  tags = map[Namespace:namespace Stage:stage Name:namespace-stage-name2-1-2-3]
}
label2_id = namespace-stage-name2-1-2-3
label2_name = name2
label2_namespace = namespace
label2_stage = stage
label2_tags = {
  Name = namespace-stage-name2-1-2-3
  Namespace = namespace
  Stage = stage
}

[osterman]

Need to incorporate the var.context["tags"] here some how

[dennybaa]

it doesn't seem possible :(

[dennybaa]

@osterman Hey, it's an awesome idea to have context.

Unfortunately I also don't see how it's possible with HCL1. We should always try to remember that scalars such as maps/list have always to be flat. Basically scalars must:

• be homogeneous
• include only simple types as string/integer/boolean

These limitations will be hopefully resolved in 0.12 if it includes HCL2...

In other words now all the variables and all the outputs should be flat and homogeneous. With the introduced context you break this rule.

Regarding non-flat scalars, the only workaround possible now is leveraging locals for intermediate computation, like bellow:

locals {
  non_flat_map = {
    map1 = "${var.map1}"  # var.map1 should be flat
    map2 = "${var.map2}"  # var.map2 should be flat
  }

  target_map = "${local.non_flat_map[var.choice ? "map1": "map2"]}"
}

output "map" {
  value = "${local.target_map}"
}

[Jamie-BitFlight]

This code:

module "label1" {
  source     = "../../"
  namespace  = "CloudPosse"
  stage      = "Production"
  name       = "Winston"
  attributes = ["fire", "water", "earth", "air"]

  tags = {
    "City"        = "Dublin"
    "Environment" = "Private"
  }
}

module "label2" {
  source  = "../../"
  context = "${module.label1.context}"
  name    = "Charlie"

  tags = {
    "City"        = "London"
    "Environment" = "Public"
  }
}
output "label1" {
  value = {
    id         = "${module.label1.id}"
    name       = "${module.label1.name}"
    namespace  = "${module.label1.namespace}"
    stage      = "${module.label1.stage}"
    attributes = "${module.label1.attributes}"
  }
}

output "label2" {
  value = {
    id         = "${module.label2.id}"
    name       = "${module.label2.name}"
    namespace  = "${module.label2.namespace}"
    stage      = "${module.label2.stage}"
    attributes = "${module.label2.attributes}"
  }
}

output "label1_tags" {
  value = "${module.label1.tags}"
}

output "label1_context" {
  value = "${module.label1.context}"
}

output "label2_tags" {
  value = "${module.label2.tags}"
}

output "label2_context" {
  value = "${module.label2.context}"
}

Makes this output now

Outputs:

label1 = {
  attributes = [fire water earth air]
  id = cloudposse-production-winston-fire-water-earth-air
  name = winston
  namespace = cloudposse
  stage = production
}
label1_context = {
  attributes = [fire water earth air]
  delimiter = [-]
  name = [winston]
  namespace = [cloudposse]
  stage = [production]
  tags_keys = [City Environment Name Namespace Stage]
  tags_values = [Dublin Private cloudposse-production-winston-fire-water-earth-air cloudposse production]
}
label1_tags = {
  City = Dublin
  Environment = Private
  Name = cloudposse-production-winston-fire-water-earth-air
  Namespace = cloudposse
  Stage = production
}
label2 = {
  attributes = [fire water earth air]
  id = cloudposse-production-charlie-fire-water-earth-air
  name = charlie
  namespace = cloudposse
  stage = production
}
label2_context = {
  attributes = [fire water earth air]
  delimiter = [-]
  name = [charlie]
  namespace = [cloudposse]
  stage = [production]
  tags_keys = [City Environment Name Namespace Stage]
  tags_values = [London Public cloudposse-production-charlie-fire-water-earth-air cloudposse production]
}
label2_tags = {
  City = London
  Environment = Public
  Name = cloudposse-production-charlie-fire-water-earth-air
  Namespace = cloudposse
  Stage = production
}

[Jamie-BitFlight]

@dennybaa I got it working

[Jamie-BitFlight]

LGTM

[osterman]

can we rename this? maybe call it null_context?

[Jamie-BitFlight]

I'm renaming it to context_struct, since it is the structure of context with all variables.

[osterman]

let's call ~^~ something (E.g. unique_separator) - either a variable or a local.

[osterman]

@dennybaa - please have another look at this. It's not pretty, but it sets out to accomplish what we wanted to do. I'm pretty sure we'll end up merging this.

[dennybaa]

@osterman Wow. That's a lot of effort, this might be a good example of that how to mitigate passing non-flat structures :)

It would be nice if you also switch to null_data_source this reduces output rubbish during plan/apply, and specifically made for this, in other words resource is an overkill here.

This would work now, though tags passing seemed reasonably easier and if I'm not mistaken achieved the same goal. My personal opinion that terraform is not yet ready for things we are trying to do... Don't get me wrong but it doesn't feel like an easy way. Though I really admire your approach and implementation 👍

[dennybaa]

So I still think, taking an approach of calling tags Name/Namespace/Stage as generated_tags. IMO it still looks neater for me to have an option like exclude_generated_tags, because it will generally keep locals computations simpler.

[Jamie-BitFlight]

I think that this will get far easier in tf 0.12

[goruha]

Looks complicated, but not too much.
Eventually we will simplify that for 0.12 tf

[dennybaa]

@osterman yeah, it looks a bit complicated, but what we can do :) The module is very usable now 👍 for it.

[dennybaa]

@osterman Hey, Erik. I've noticed it seems that you missed https://github.com/stackfeed/terraform-null-label/commit/4d7fb86ab793edb4664ab7bef422fc80b84bfcd0