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Regula is a tool that evaluates Terraform infrastructure-as-code for potential AWS, Azure, and Google Cloud security misconfigurations and compliance violations prior to deployment.

Regula diagram

Regula includes a library of rules written in Rego, the policy language used by the Open Policy Agent (opa) project. Regula works with your favorite CI/CD tools such as Jenkins, Circle CI, and AWS CodePipeline; we’ve included a GitHub Actions example so you can get started quickly (see our blog post here). Where relevant, we’ve mapped Regula policies to the CIS AWS, Azure, and GCP Foundations Benchmarks so you can assess your compliance posture. We'll be adding more rules in the coming weeks, sourced from Fugue.

How does Regula work?

There are two parts to Regula. The first is a shell script that generates a terraform plan or use existing in JSON format, ready for consumption by opa.

The second part is a Rego framework that:

  • Merges resource info from planned_values and configuration in the Terraform plan into a more conveniently accessible format.
  • Walks through the imported Terraform modules and merges them into a flat format.
  • Looks for rules and executes them.
  • Creates a report with the results of all rules and a control mapping in the output.

Rule library

See rules directory. Fugue is currently working on open sourcing more rules from our product to Regula.

Provider Service Rule Name Rule Summary
AWS CloudFront cloudfront_distribution_https CloudFront distributions should use HTTPS traffic
AWS CloudTrail cloudtrail_log_file_validation CloudTrail log file validation should be enabled
AWS EBS ebs_volume_encrypted EBS volume encryption should be enabled
AWS IAM iam_admin_policy IAM policies should not have full ":" administrative privileges
AWS IAM iam_user_attached_policy IAM policies should not be attached directly to users
AWS KMS kms_rotate KMS CMK rotation should be enabled
AWS S3 s3_bucket_sse Server Side Encryption by default should be set for S3 buckets
AWS VPC security_group_ingress_anywhere VPC security group rules should not permit ingress from '' except to ports 80 and 443
AWS VPC security_group_ingress_anywhere_rdp VPC security group rules should not permit ingress from '' to port 3389 (Remote Desktop Protocol)
AWS VPC security_group_ingress_anywhere_ssh VPC security group rules should not permit ingress from '' to port 22 (SSH)
AWS VPC vpc_flow_log VPC flow logging should be enabled
GCP KMS kms_cryptokey_rotate KMS crypto keys should be rotated at least once every 365 days
GCP Compute compute_firewall_no_ingress_22 VPC firewall rules should not permit ingress from '' to port 22 (SSH)
GCP Compute compute_firewall_no_ingress_3389 VPC firewall rules should not permit ingress from '' to port 3389 (RDP)
GCP Compute compute_subnet_private_google_access VPC subnet 'Private Google Access' should be enabled
GCP Compute compute_subnet_flow_log_enabled VPC subnet flow logging should be enabled
Azure Storage Account storage_account_deny_access Storage accounts should deny access from all networks by default
Azure Storage Account storage_account_microsoft_services Storage accounts 'Trusted Microsoft Services' access should be enabled
Azure Storage Account storage_account_secure_transfer Storage accounts 'Secure transfer required' should be enabled
Azure Blob Storage storage_container_private_access Storage containers should have access set to 'private'
Azure Virtual Network network_security_group_no_inbound_22 Network security group rules should not permit ingress from '' to port 22 (SSH)
Azure Virtual Network network_security_group_no_inbound_3389 Network security group rules should not permit ingress from '' to port 3389 (RDP)
Azure SQL Server sql_server_firewall_no_inbound_all SQL Server firewall rules should not permit ingress from to all ports and protocols

Running Regula locally

Install the prerequisites:

macOS and Linux

Run the following command:

./bin/regula [TERRAFORM_PATH] [REGO_PATHS...]

TERRAFORM_PATH is the directory where your Terraform configuration files are located.

REGO_PATHS are the directories that need to be searched for Rego code. This should at least include lib/.

Some examples:

  • ./bin/regula ../my-tf-infra .: conveniently check ../my-tf-infra against all rules in this main repository.
  • ./bin/regula ../my-tf-infra.json .: conveniently check ../my-tf-infra.json terraform plan against all rules in this main repository.
  • ./bin/regula ../my-tf-infra lib examples/aws/ec2_t2_only.rego: run Regula using only the specified rule.
  • ./bin/regula ../my-tf-infra lib ../custom-rules: run Regula using a directory of custom rules.

It is also possible to set the name of the terraform executable, which is useful if you have several versions installed:

env TERRAFORM=terraform-v0.12.18 ./bin/regula ../regula-ci-example/ lib

Note that Regula requires Terraform 0.12+ in order to generate the JSON-formatted plan.


Because Regula uses a bash script to automatically generate a plan, convert it to JSON, and run the Rego validations, Windows users can instead manually run the steps that Regula performs. See those steps here. Alternatively, you can run the script using WSL.

Regula rules

Regula rules are written in standard Rego and use a similar format to Fugue Custom Rules. This means there are (currently) two kinds of rules: simple rules and advanced rules.

Simple rules

Simple rules are useful when the policy applies to a single resource type only, and you want to make simple yes/no decision.

# Rules must always be located right below the `rules` package.
package rules.my_simple_rule

# Simple rules must specify the resource type they will police.
resource_type = "aws_ebs_volume"

# Simple rules must specify `allow` or `deny`.  For this example, we use
# an `allow` rule to check that the EBS volume is encrypted.
default allow = false
allow {
  input.encrypted == true

Custom error messages

If you want to return more information to the user, you can also define a custom error message. This is done by writing a deny[msg] style rule.

package rules.simple_rule_custom_message
resource_type = "aws_ebs_volume"

deny[msg] {
  not input.encrypted
  msg = "EBS volumes should be encrypted"

Advanced rules

Advanced rules are harder to write, but more powerful. They allow you to observe different kinds of resource types and decide which specific resources are valid or invalid.

# Rules still must be located in the `rules` package.
package rules.user_attached_policy

# Advanced rules typically use functions from the `fugue` library.
import data.fugue

# We mark an advanced rule by setting `resource_type` to `MULTIPLE`.
resource_type = "MULTIPLE"

# `fugue.resources` is a function that allows querying for resources of a
# specific type.  In our case, we are just going to ask for the EBS volumes
# again.
ebs_volumes = fugue.resources("aws_ebs_volume")

# Auxiliary function.
is_encrypted(resource) {
  resource.encrypted == true

# Regula expects advanced rules to contain a `policy` rule that holds a set
# of _judgements_.
policy[p] {
  resource = ebs_volumes[_]
  p = fugue.allow_resource(resource)
} {
  resource = ebs_volumes[_]
  not is_encrypted(resource)
  p = fugue.deny_resource(resource)

The fugue API consists of four functions:

  • fugue.resources(resource_type) returns an object with all resources of the requested type.
  • fugue.allow_resource(resource) marks a resource as valid.
  • fugue.deny_resource(resource) marks a resource as invalid.
  • fugue.missing_resource(resource_type) marks a resource as missing. This is useful if you for example require a log group to be present.

Rule examples

Whereas the rules included in the Regula rules library are generally applicable, we've built rule examples that look at tags, region restrictions, and EC2 instance usage that should be modified to fit user/organization policies.

Provider Service Rule Name Rule Description
AWS EC2 ec2_t2_only Restricts instances to a whitelist of instance types
AWS IAM iam_password_length Requires IAM Password Policies with a certain minimum password length
AWS Tags tag_all_resources Checks whether resources that are taggable have at least one tag with a minimum of 6 characters
AWS Regions useast1_only Restricts resources to a given AWS region

Compliance controls vs. rules

What's the difference between controls and rules? A control represents an individual recommendation within a compliance standard, such as "IAM policies should not have full "*:*" administrative privileges" (CIS AWS Foundations Benchmark 1-22).

In Regula, a rule is a Rego policy that validates whether a cloud resource violates a control (or multiple controls). One example of a rule is iam_admin_policy, which checks whether an IAM policy in a Terraform file has "*:*" privileges. If it does not, the resource fails validation.

Controls map to sets of rules, and rules can map to multiple controls. For example, control CIS_1-22 and REGULA_R00002 both map to the rule iam_admin_policy.

Specifying compliance controls

Controls can be specified within the rules: just add a controls set.

# Rules must always be located right below the `rules` package.
package rules.my_simple_rule

# Simple rules must specify the resource type they will police.
resource_type = "aws_ebs_volume"

# Controls.
controls = {"CIS_1-16"}

# Rule logic

Interpreting the results

Here's a snippet of test results from a Regula report. The output is from an example GitHub Action:

  "result": [
      "expressions": [
          "value": {
            "controls": {
              "CIS_1-22": {
                "rules": [
                "valid": false
            "rules": {
              "iam_admin_policy": {
                "resources": {
                  "aws_iam_policy.basically_allow_all": {
                    "id": "aws_iam_policy.basically_allow_all",
                    "message": "invalid",
                    "type": "aws_iam_policy",
                    "valid": false
                  "aws_iam_policy.basically_deny_all": {
                    "id": "aws_iam_policy.basically_deny_all",
                    "message": "",
                    "type": "aws_iam_policy",
                    "valid": true
                "valid": false
            "summary": {
              "controls_failed": 2,
              "controls_passed": 12,
              "rules_failed": 2,
              "rules_passed": 8,
              "valid": false
          "text": "",
          "location": {
            "row": 1,
            "col": 1

These are the important bits:

  • Summary
  • Controls
  • Rules


The summary block contains a breakdown of the compliance state of your Terraform files. In the output above, the Terraform violated 2 rules and 2 controls, so the test as a whole failed.


Regula shows you compliance results for both controls and rules, in addition to which specific resources failed. Above, in the controls block, you can see that the Terraform in the example is noncompliant with CIS_1-22, and the mapped rules that failed are listed underneath (in this case, iam_admin_policy).


In the rules block further down from controls, each rule lists the resources that failed. Above, you'll see that the resource aws_iam_policy.basically_allow_all was the one that failed the mapped rule -- as noted by "valid": false. In contrast, aws_iam_policy.basically_deny_all passed.

You can see the full example report in this GitHub Action log. For a detailed explanation of the report, see the regula-ci-example README.

Running Regula in CI

Regula is designed to be easy to run in CI. We provide a GitHub Action that can be easily added to your repository:

Setting up Regula with different CI/CD solutions such as Jenkins, CodePipeline, CircleCI, TravisCI, and others would follow a similar pattern. This repository contains an example:

Running Regula with Conftest

Conftest is a test runner for configuration files that uses Rego for policy-as-code. Conftest supports Terraform; but policies need to be written directly against the plan file which is often inconvenient and tricky.

Since Regula is just a Rego library; it works works seamlessly with Conftest. This way you get the advantages of both projects, in particular:

  • Easy CI integration and policy retrieval from Conftest
  • Terraform plan parsing & the rule set from Regula

To use Regula with Conftest:

  1. Generate a plan.json using the following terraform commands:

    terraform init
    terraform plan -refresh=false -out=plan.tfplan
    terraform show -json plan.tfplan >plan.json
  2. Now, we'll pull the conftest support for Regula and the Regula library in.

    conftest pull -p policy/
    conftest pull -p policy/regula/lib

    If we want to use the rules that come with regula, we can use:

    conftest pull -p policy/regula/rules

    And of course you can pull in your own Regula rules as well.

  3. As this point, it's simply a matter of running conftest!

    conftest test plan.json


Directory structure

  • bin/: the main Regula script that calls terraform & opa.
  • lib/: the OPA library code to evaluate rules and mangle input.
  • rules/: a collection of rules. We may split this up further as the number of rules increases.
  • examples/: a collection of example rules that you can use as inspiration for your own rules.
  • scripts/: scripts for development; currently only a script to generate test input.
  • tests/:
    • tests/lib: internal tests for the library.
    • tests/rules/: tests for the various rules.
    • tests/rules/inputs: terraform files that can be used to generate Rego files.
    • tests/examples/: tests for the example rules.
    • tests/examples/inputs: input files for the example rules.

Adding a test

If you would like to add a rule, we recommend starting with a test. Put your terraform code in a file in tests/rules/<provider>/inputs; for example tests/rules/aws/inputs/ From this, you can generate a mock input by running:

bash scripts/

The mock input will then be placed in a .rego file with the same name, in our case tests/rules/aws/inputs/kms_rotate_infra.rego.

Next, add the actual tests to a Rego file with the same name (appended with _test instead of _infra), but outside of the inputs/ subdirectory. Using this example, that would be tests/rules/aws/kms_rotate_test.rego.

Debugging a rule with fregot

Once you have generated the mock input, it is easy to debug a rule with fregot. Fire up fregot with the right directories and set a breakpoint on the rule you are trying to debug:

$ fregot repl lib rules tests
F u g u e   R E G O   T o o l k i t
fregot v0.7.2 repl - use :help for usage info
repl% :break data.rules.ec2_t2_only.allow

Now, we can just evaluate the entire report with the mock input. If your rule is triggered, that will drop you into a debug prompt:

repl% with input as data.tests.rules.ec2_t2_only.mock_input
19|   valid_instance_types[input.instance_type]

From here, you can evaluate anything in context; such as input to look at the resource, or any other auxiliary rules such as valid_instance_types in this example.

Locally producing a report

In some cases (such as development and testing), you may want to manually reproduce the steps that Regula performs automatically. If that is something you want to step through, this section is for you.

We first need to obtain a JSON-formatted terraform plan. In order to do get that, you can use:

terraform init
terraform plan -refresh=false -out=plan.tfplan
terraform show -json plan.tfplan >input.json

This gives you input.json. Now you can test this input against the rules by evaluating with OPA. In order to do that, point OPA to the input file, and the regula project directory.

opa eval -d /path/to/regula --input input.json ''

Or using fregot:

fregot eval --input input.json '' . | jq

If all goes well, you should now see the results for each rule.

Locally producing a report on Windows

To locally produce a Regula report on Windows, use the following steps:

  1. Generate a JSON-based terraform plan:

    .\terraform.exe init
    .\terraform.exe plan -refresh=false -out=infra
    .\terraform.exe show -json infra >infra.json
  2. Run OPA against this input file:

    .\opa_windows_amd64.exe eval -i .\infra.json -d .\regula\lib\ -d .\regula\rules\ ''


Regula checks Terraform for AWS, Azure and GCP security and CIS compliance using Open Policy Agent/Rego




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