Is it possible to turn the access_logs block on and off via the environment_name variable?

One way to achieve this with TF 0.12 onwards is to use dynamic blocks:

dynamic "access_logs" {
  for_each = var.environment_name == "production" ? [var.environment_name] : []
  content {
    bucket  = "my-bucket"
    prefix  = "${var.environment_name}-alb"
  }
}

This will create one or zero access_logs blocks depending on the value of var.environment_name.

In the current terraform, the if statement is only a value and can not be used for the block.

There is a workaround in this case. You can set the enabled attribute of the access_log block to false. Note that this is not a general solution but can only be used with the access_log block.

access_logs {
    bucket  = "my-bucket"
    prefix  = "${var.environment_name}-alb"
    enabled = "${var.environment_name == "production" ? true : false }"
}

See also:

• https://www.terraform.io/docs/providers/aws/r/elb.html#access_logs
• https://www.terraform.io/docs/providers/aws/r/alb.html#access_logs
• https://github.com/hashicorp/terraform/pull/11120

Expanding on Juho Rutila's answer as it's too much to fit in a comment.

This is possible using dynamic blocks from v0.12, but I found the properties had to be included in a nested content block. The for_each statement is also a bit tricky, so I found it sensible to extract that into a local to make the important stuff more readable:

locals {
  isProd = var.environment_name == "production" ? [1] : []

  // Not necessary, but just illustrating that the reverse is possible
  isNotProd = var.environment_name == "production" ? [] : [1]
}

dynamic "access_logs" {
  for_each = local.isProd
  content {
    bucket  = "my-bucket"
    prefix  = "${var.environment_name}-alb"
  }
}

You can read more about dynamic blocks here: https://www.terraform.io/docs/configuration/expressions.html#dynamic-blocks