Marcus Young

Software. Microcontrollers. Beer.

Vault Roles/Policies in Terraform

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Now we get to the fun part and put everything we need from Vault in terraform.

If you’ve used ECS and Vault with the aws auth backend you may have found a bit of a snag in terms of automation.

Lets say you want to create a new ECS container to run. You want that task to get specific secrets in vault by role. You write the code, terraform, etc and when it runs you get:

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URL: GET http://server:8200/v1/auth/aws-ec2/role/somerole
Code: 400. Errors:

* entry for role somerole not found

So you deployed something but now you have to create a policy, a role, etc in vault via the CLI, all the while your task is throttling.

Little known fact: the terribly-named vault_generic_secret from the provider docs can do create roles/policies in addition to secrets (hence the bad name).

In this part 2 I’ll show you how to automate the next step of your ECS task into terraform so there’s no race condition.

Prerequisites

  1. Vault running as a server
  2. Vault CLI to match the server
  3. Terraform

Create a vault policy in terraform

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resource "vault_generic_secret" "policy" {
  path = "sys/policy/${aws_iam_role.neutrona_wand.name}"

  data_json = <<EOT
{
  "name": "${aws_iam_role.neutrona_wand.name}",
  "rules": "path \"secret/ops/*\" {\n  policy = \"read\"\n}\n\npath \"secret/common/*\" {\n  policy = \"read\"\n}"
}

EOT
}

Create an AWS auth role in terraform

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provider "vault" {}

resource "aws_iam_role" "neutrona_wand" {
  name = "neutrona_wand"
  path = "/lambda/"

  assume_role_policy = <<POLICY
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "",
      "Effect": "Allow",
      "Principal": {
        "Service": [
          "lambda.amazonaws.com"
        ]
      },
      "Action": "sts:AssumeRole"
    }
  ]
}
POLICY
}

# The ugly replace in 'bound_iam_principal_arn' is to account for removing the path from the role. 
# If you look, my IAM role is /lambda/, so the arn would be 'arn:aws:iam::1234567890:role/lambda/neutrona_wand'
# While the 'bound_iam_principal_arn' wants the non-path version: 'arn:aws:iam::1234567890:role/neutrona_wand'
resource "vault_generic_secret" "role" {
  path = "auth/aws/role/${aws_iam_role.neutrona_wand.name}"

  data_json = <<EOT
{
  "bound_iam_principal_arn": "${replace(aws_iam_role.neutrona_wand.arn, "/:role\\/[a-zA-Z\\/]*\\//", ":role\\/")}",
  "policies": "default,${aws_iam_role.neutrona_wand.name},slack",
  "max_ttl":"300",
  "resolve_aws_unique_ids": "false"
}
EOT
}

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