Terraform Dynamic module from a map

Question

I'm trying to generate a dynamic aws_db_parameter_group from a map in terraform. I was wondering if what I'm trying to do is even possible. Here is a sample code:

provider "aws" {
...
}

variable "key_values" {
  type = map(string)

  default = {
    "audit_trail" = "db,extended"
    "log_buffer" = "100"
  }
}

resource "aws_db_parameter_group" "test" {
  family = "oracle-ee"

  name = "test"

  dynamic "key_value" {
    for_each = var.key_values
    content {
        name = key_value.key
        value = key_value.value
    }
  }
}

The goal is that for each key, value in my variable, I want to generate a dynamic block with two values. One would be the key name and the second value would be value in the map. I've been reading this: https://www.terraform.io/docs/language/expressions/dynamic-blocks.html

And it looks like it is doable what I'm trying but I can't figure it out. Any suggestion?

Regards,

Hugo Lesta · Accepted Answer · 2022-01-06 16:15:59Z

1

According to the documentation, the only possible dynamic block you can use is parameter I'll give you an example below.

resource "aws_db_parameter_group" "default" {
  name = "db-paramgroup-${var.project}-${var.env}"
  family = "mysql${var.engine_version}"

  dynamic "parameter" {
    for_each = var.custom_db_parameters
    content {
      name         = lookup(parameter.value, "name", null)
      value        = lookup(parameter.value, "value", null)
      apply_method = lookup(parameter.value, "apply_method", null)
    }
  }
  tags = var.tags
}

If you need to create multiple aws_db_parameter_groupresources in a dynamic way, you should use a count or for_each to make it work, I'll give you a new example below.


resource "aws_db_parameter_group" "default" {
  count = length(var.parameter_group_name) == 0 ? 1 : 0
  name = "db-paramgroup-${var.project}-${var.env}"
  family = "mysql${var.engine_version}"

  dynamic "parameter" {
    for_each = var.custom_db_parameters
    content {
      name         = lookup(parameter.value, "name", null)
      value        = lookup(parameter.value, "value", null)
      apply_method = lookup(parameter.value, "apply_method", null)
    }
  }
  tags = var.tags
}

in case you need more information about how a count works, you can refer to this link.

In addition, make sure you are using custom_db_parameters values like the following:

custom_db_parameters = [
    {
      name        = "database_parameter_name_one"
      value = "database_parameter_value_one"
      apply_method  = "immediate"

    },
    {
      name        = "database_parameter_name_two"
      value = "database_parameter_value_two"
      apply_method  = "pending-reboot"
    },

]

Make sure to have a proper value for the apply_method key, you have two possible values and it's important to understand if you need to apply it immediately or wait for the next reboot/maintenance window.

edited Jan 6, 2022 at 16:15

answered Dec 9, 2021 at 15:10

Hugo Lesta

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9 Comments

amir Over a year ago

Thank you very much Hugo. I'm having a look at the lookup.

Hugo Lesta Over a year ago

My pleasure, I hope it may help you!

user8072466 Over a year ago

Did this work? I tried the same approach as mentioned above, but the lookup function always returns the default value "immediate".

Hugo Lesta Over a year ago

Yes, this code should work, the lookup built-in function is validating the values you pass through the variable called custom_db_parameters into the for_each parameter, make sure you are passing the right value and then you can get the elements, notice if the value is not there, the lookup function will return a null by default (example above)

amir Over a year ago

Hi, this code used to work but today, when I try, I got an error like this: │ Invalid value for "inputMap" parameter: lookup() requires a map as the first argument. Any idea?

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