AWS STS Role

This Ansible role allows a user to assume a given role, generating temporary security credentials that can be used to assume the role.

Requirements

• Python 2.7 or 3.6
• PIP package manager
• Ansible 2.5 or greater (pip install ansible)
• AWS CLI (pip install awscli)

Setup

To use this role, you must add the rola as Ansible Galaxy requirement to your Ansible playbook project.

To set this role up as an Ansible Galaxy requirement, first create a requirements.yml file in a subfolder called roles and add an entry for this role. See the Ansible Galaxy documentation for more details.

# Example requirements.yml file
- src: git@github.com:Casecommons/aws-sts.git
  scm: git
  version: 0.1.0
  name: aws-sts

Once you have created roles/requirements.yml, you can install the role using the ansible-galaxy command line tool.

$ ansible-galaxy install --role-file=roles/requirements.yml --roles-path=./roles/ --force
$ git commit -a -m "Added aws-sts 0.1.0 role"

To update the role version, simply update the requirements.yml file and re-install the role as demonstrated above.

Usage

Inputs

The STS role relies on a top level Sts object that uses the following inputs:

• Sts.Profile (Conditional) - defines the local AWS profile that credentials should be obtained from.
• Sts.Role (Optional) - defines the ARN of the role to assume. If configured, this will override the role associated with the detected/configured profile.
• Sts.SessionName (Optional) - a name for the temporary session token that is generated
• Sts.Disabled (Optional) - disables the assume role action of this role. Useful for long running playbooks that would be affected by the duration (maximum 60 minutes) of using STS token. You must set this flag whenever you use explicit AWS credentials in your local environment (e.g. you have configured access key, secret access key and session token as environment variables) and you don't want to attempt to assume a role.
• Sts.Region (Optional) - the target AWS region. Alternatively you can set the AWS region using the AWS_DEFAULT_REGION environment variable. If this is not in your environment, the playbook defaults to us-west-2.
• AWS credentials - you must configure the environment such that your credentials are available to assume the role. For example, you can set an access key and secret key via environment variables, or configure a profile via environment variables, or rely on an EC2 instance profile if running in AWS. A dictionary called Sts.Credentials is output by this module, which sets up the appropriate configuration with AWS STS token settings.

Outputs

If the assume role operation is successful, the temporary credentials issued by AWS are registered to Sts.Credentials:

• Sts.Credentials.AWS_ACCESS_KEY
• Sts.Credentials.AWS_ACCESS_KEY_ID
• Sts.Credentials.AWS_SECRET_KEY
• Sts.Credentials.AWS_SECRET_ACCESS_KEY
• Sts.Credentials.AWS_SECURITY_TOKEN
• Sts.Credentials.AWS_DEFAULT_REGION

You can configure Sts.Credentials as the environment for subsequent plays to operate under the privileges of the assumed role:

AWS_DEFAULT_REGION: "{{ Sts.Credentials.AWS_DEFAULT_REGION }}"
AWS_ACCESS_KEY: "{{ Sts.Credentials.AWS_ACCESS_KEY }}"
AWS_ACCESS_KEY_ID: "{{ Sts.Credentials.AWS_ACCESS_KEY_ID }}"
AWS_SECRET_KEY: "{{ Sts.Credentials.AWS_SECRET_KEY }}"
AWS_SECRET_ACCESS_KEY: "{{ Sts.Credentials.AWS_SECRET_ACCESS_KEY` }}"
AWS_SECURITY_TOKEN: "{{ Sts.Credentials.AWS_SECURITY_TOKEN` }}"

You should call this role from a dedicated play, and then define your subsequent playbook tasks in separate plays. This allows the sts_creds or individual sts_session variables to be used to configure the environment of your remaining tasks.

Role Assumption Behavior

By default this role attempts to determine an STS role to assume using the following rules in order of precedence:

1. Use the role defined by Sts.Role
2. Lookup the role defined in the specified AWS profile if Sts.Profile is configured
3. Lookup the role defined in the specified AWS profile if the AWS_PROFILE environment variable is set

This role also attempts to determine your AWS region using the following rules in order of precedence:

1. Use the value of Sts.Region if defined
2. Use the value of the AWS_DEFAULT_REGION or AWS_REGION environment variables if set
3. Use the region defined in your current AWS profile if configured
4. Return an error if none of the above methods can determine your region

In order to assume the role, this role attempts to determine your AWS credentials using the following rules in order of precedence:

1. Use the AWS profile defined by Sts.Profile
2. Use the AWS profile in the specified AWS profile is the AWS_PROFILE environment variable is set
3. Use standard AWS environment variables if configured

Examples

The following demonstrates how to call this role from a playbook:

- name: Assume Role Play
  hosts: localhost
  connection: local
  gather_facts: no
  vars:
    Sts:
      Role: arn:aws:iam::123456789:role/admin
      SessionName: testAssumeRole
      Region: us-west-2
  roles:
    - aws-sts

The following shows the recommended play configuration to use the temporary credentials issued:

...
...
- name: My Playbook
  hosts: localhost
  connection: local
  environment: "{{ Sts.Credentials }}"
  tasks:
   - ...
   - ...
...
...

Testing

You can run the included test.yml playbook to test this role directly.

To test the role you need to provide the role that you want to assume as demonstrated below:

$ ansible-playbook test.yml -e Sts.Role=arn:aws:iam::429614120872:role/admin
PLAY [Assume Role] *************************************************************

TASK [set_fact] ****************************************************************
ok: [localhost]

TASK [checking if sts functions are sts_disabled] ******************************
skipping: [localhost]

TASK [setting empty sts_session result] ****************************************
skipping: [localhost]

TASK [setting sts_creds if legacy AWS credentials are present (e.g. for Ansible Tower)] ***
skipping: [localhost]

TASK [assume sts role] *********************************************************
ok: [localhost]

TASK [set sts facts] ***********************************************************
ok: [localhost]

TASK [set sts facts] ***********************************************************
ok: [localhost]

TASK [debug] *******************************************************************
skipping: [localhost]

TASK [debug] *******************************************************************
ok: [localhost] => {
    "msg": {
        "AWS_ACCESS_KEY": "xxxx",
        "AWS_ACCESS_KEY_ID": "xxxx",
        "AWS_DEFAULT_REGION": "ap-southeast-2",
        "AWS_SECRET_ACCESS_KEY": "xxxx",
        "AWS_SECRET_KEY": "xxxx",
        "AWS_SECURITY_TOKEN": "xxxx"
    }
}

PLAY RECAP *********************************************************************
localhost                  : ok=5    changed=0    unreachable=0    failed=0

Release Notes

Version 2.7

• Ansible 2.7 support
• Python 3 support

Version 2.5

• Ansible 2.5 support

Version 2.4.1

• Improve region handling

Version 2.4.0

• Ansible 2.4 support
• Add profile detection feature

Version 1.0

• Switch to dot notation syntax

Version 0.1.3

• Add Licensing Information

Version 0.1.2

• Fix incorrect sts_session references

Version 0.1.1

• Update command to use non abbreviated options.

Version 0.1.0

• First Release

License

Copyright (C) 2017. Case Commons, Inc.

This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more details.

See www.gnu.org/licenses/agpl.html