Ansible Tower for Continuous Infrastructure

As infrastructure and teams scale, effective and robust configuration management requires growing beyond manual processes and local conventions. Fortunately, Ansible Tower (or the upstream Open Source project Ansible AWX) provides a perfect platform for configuration management at scale.

The Ansible Tower/AWX documentation and tutorials provide comprehensive information about the individual components.  However, assembling all the moving pieces into a whole working solution can involve some trial and error and reverse engineering in order to understand how the components relate to one another.  Ansible Tower, like the core Ansible solution, offers flexibility in how features assembled to support different typed of workflows. The types of workflows can include once-off initial configurations, ad-hoc system maintenance, or continuous convergence.

Continuous convergence, also referred to as desired state, regularly re-applies the defined configuration to infrastructure. This tends to ‘correct the drift’ often encountered when only applying the configuration on infrastructure setup. For example, a continuous convergence approach to configuration management could apply the desired configuration on a recurring schedule of every 30 minutes.  

Some continuous convergence workflow characteristics can include:

  • Idempotent Ansible roles. If there are no required configuration deviations, run will report 0 changes.
  • A source code repository per Ansible role, similar to the Ansible Galaxy approach,
  • A source code repository for Ansible playbooks that include the individual Ansible roles,
  • A host configured to provide one unique service function only,
  • An Ansible playbook defined for each unique service function that gets applied to the host,
  • Playbooks applied to each host on a repeating schedule.

One way to achieve a continuous convergence workflow combines the Ansible Tower components according to the following conceptual model.

The Workflow Components

Playbook and Role Source Code

Ansible roles contain the individual tasks, handlers, and content with a role responsible for the installation and configuration of a particular software service.

Ansible playbooks configure a host for a particular service function in the environment acting as a wrapper for the individual role based configurations.  All the roles expected to be applied to a host must be defined in the playbook.

Source Code Repositories

Role git repositories contain the versioned definition of a role, e.g. one git repository per individual role.  The roles are pulled into the playbooks using the git reference and tags, which pegs the role version used within a playbook.

Project git repositories group the individual playbooks into single collection, e.g. one git repository per set of playbooks.  As with roles, specific versions of project repositories are also identified by version tags. 

Ansible Tower Server

Two foundational concepts in Ansible Tower are projects and inventories. Projects provide access to playbooks and roles. Inventories provide the connection to “real” infrastructure.  Inventories and projects also provide authorisation scope for activities in Ansible Tower. For example, a given group can use the playbooks in Project X and apply jobs to hosts in Inventory Y.

Each Ansible Tower Project is backed by a project git repository.  Each repository contains the playbooks and included roles that can be applied by a given job.  The Project is the glue between the Ansible configuration tasks and the plays that apply the configuration.

Ansible Tower Inventories are sets of hosts grouped for administration, similar to inventory sets used when applying playbooks manually.  One option is to group hosts into Inventories by environment.  For example, the hosts for development may be in one Inventory while the hosts for production may be in another Inventory.  User authorisation controls are applied at the Inventory level.

Ansible Tower Inventory Groups define sub-sets of hosts within the larger Inventory.  These subsets can then be used to limit the scope of a playbook job.  One option is to group hosts within an Inventory by function.  For example, the hosts for web servers may be in one Inventory Group and the hosts for databases may be in another Inventory Group.  This enables one playbook to target one inventory group.  Inventory groups effectively provide metadata labels for hosts in the Inventory.

An Ansible Job Template determines the configuration to be applied to hosts.  The Job Template links a playbook from a project to an inventory.   The inventory scope can be optionally further limited by specifying inventory group limits.  A Job Template can be invoked either on an ad-hoc basis or via a recurring schedule.

Ansible Job Schedules define the time and frequency at which the configuration specified in the Job Template is applied.  Each Job Template can be associated with one or more Job Schedules.  A schedule supports either once-off execution, for example during a defined change window, or regularly recurring execution.  A job schedule that applies the desired state configuration with a frequency of 30 minutes provides an example of a job schedule used for a continuous convergence workflow.

“Real” Infrastructure

An Ansible Job Instance defines a single invocation of an Ansible Job Template, both for scheduled and ad-hoc invocations of the job template.  Outside of Ansible Tower, the Job Instance is the equivalent of executing the ansible-playbook command using an inventory file.

Host is the actual target infrastructure resources configured by the job instance, applying an ansible playbook of included roles.

A note on Ansible Variables

As with other features of Ansible and Ansible Tower, variables also offer flexibility in defining parameters and context when applying a configuration.  In addition to declaring and defining variables in roles and playbooks, variable definitions can also be defined in Ansible Tower job templates, inventory and inventory groups, and individual hosts.  Given the plethora of options for variable definition locations, without a set of conventions for managing variable values, debugging runtime issues with roles and playbooks can become difficult.  E.g. which value defined at which location was used when applying the role?

One example of variable definitions conventions could include:

  • Variables shall be given default values in the role, .e.g. in the ../defaults/main.yml file.
  • If the variable must have a ‘real’ value supplied when applying the playbook, the variable shall be defined with an obvious placeholder value which will fail if not overridden.
  • Variables shall be described in the role README.md documentation
  • Do not apply variables at the host inventory level as host inventory can be transient.
  • Variables that select specific capabilities within a role shall be defined at the Ansible Tower Inventory Group.  For example, a role contains the configuration definition for both master and work nodes.  The Inventory Group variables are used to indicate which hosts must have the master configuration and applied and which must have the worker configuration applied.
  • Variables that define the environment context for configuration shall be defined in the Ansible Tower Job Template.

Following these conventions, each of the possible variable definition options serves a particular purpose.  When an issue with variable definition does arise, the source is easily identified.

Managing Secrets in CICD Pipelines

Overview

With the adoption automation for deploying and managing application environments, protecting privileged accounts and credential secrets in a consistent, secure, and scalable manner becomes critical.  Secrets can include account usernames, account passwords and API tokens.  Good credentials management and secrets automation practices reduce the risk of secrets escaping into the wild and being used either intentionally (hacked) or unintentionally (accident).

  • Reduce the likelihood of passwords slipping into source code commits and getting pushed to code repositories, especially public repositories such as github.
  • Minimise the secrets exposure surface area by reducing the number of people who require knowledge of credentials.  With an automated credentials management process that number can reach zero.
  • Limit the useful life of a secret by employing short expiry times and small time-to-live (TTL) values.  Automation enables reliable low-effort secret re-issue and rotation.

Objectives

The following objectives have been considered in designing a secrets automation solution that can be integrated into an existing CICD environment.

  • Integrate into an existing CICD environment without requiring an “all or nothing” implementation.  Allow existing jobs to operate alongside jobs that have been converted to the new secrets automation solution.
  • A single design that can be applied across different toolchains and deployment models.  For example, deployment to a Kubernetes environment can use the same secrets management process as an application installation on a virtual machine.  Similarly, the design can be used with different CICD tools, such as GitLab-CI, Travis-CI, or other build and deploy automation tool.
  • Multi-cloud capable by limiting coupling to a specific hosting environment or cloud services provider.
  • The use of secrets (or not) can be decided at any point in time, without requiring changes to the CICD job definition, similar to the use of feature flags in applications.
  • Enable changes to secrets, either due to rotation or revocation, to be maintained from a central service point.  Avoid storing the same secret multiple times in different locations.
  • Secrets organised in predictable locations in a “rest-ish” fashion by treating secrets and credentials as attributes of entities.
  • Use environment variables as the standard interface between deployment orchestration and deployed application, following the 12 Factor App approach.

Solution

  • Secrets stored centrally in Hashicorp Vault.
  • CICD jobs retrieve secrets from Vault and configure the application deployment environment.
  • Deployed applications use the secrets supplied by CICD job to access backend services.
CICD Secrets with Vault

Storing Secrets

Use Vault by Hashicorp as a centralised secrets storage service.  The CICD service retrieves secrets information for integration and deployment jobs.  Vault provides a flexible set of features to support numerous different workflows and available as either Vault Open Source or Vault Enterprise.  The secrets management pattern described uses the Vault Open Source version.  The workflow described here can be explored using Vault in the unsecured development mode, however, a properly configured and managed Vault service is required for production use.

Vault supports a number of secrets backends and access workflow models.  This solution makes use of the Vault AppRole method, which is designed to support machine-to-machine automated workflows.  With the AppRole workflow model human access to secrets is minimised through the use of access controls and temporary credentials with short TTL’s.  Within Vault, secrets are organised using an entity centric “rest-ish” style approach ensuring a given secret for a given service is stored in a single predictable location.

The use of Vault satisfies several of the design objectives:

  • enables single point management of secrets. The secrets content is stored in a single location referenced at CICD job runtime.  On the next invocation, the CICD job retrieves the latest version of the secrets content.
  • enables storing secrets in predictable locations with file system directory style path location.  The “rest-ish” approach to organising secret locations enables storing a given secret only once.  Access policies provide the mechanism to limit CICD  visibility to only those secrets required for the CICD job.

Passing Secrets to Applications

Use environment variables to pass secrets from the CICD service to the application environment.  

There are existing utilities available for populating a child process environment with Vault sourced secrets, such as vaultenv or envconsul.  This approach works well for running an application service.  However, with CICD, often there are often sets of tasks that require access to secrets information as opposed to a single command.  Using the child environment approach would require wrapping each command in a CICD job step with the env utility.  This works against the objective of introducing a secrets automation solution into existing CICD jobs without requiring substantial refactoring.  Similarly, some CICD solutions such as Jenkins provide Vault integration plugins which pre-populate the environment with secrets content.  This meets the objective of minimal CICD job refactoring, but closely couples the solution to a particular CICD service stack, reducing portability.  

With a job script oriented CICD automation stack like GitLab-CI or Travis-CI, an alternative is to insert a job step at the beginning of a series of CICD tasks that will populated the required secret values into expected environment variables.  Subsequent tasks in the job can then execute without requiring refactoring.  The decision on whether to source a particular environment variable’s content directly from the CICD job setup or from the Vault secrets store can be made by adding an optional prefix to environment variables to be sourced from the Vault secrets store.  The prefixed instance of the environment variable contains the location or path to the required secret.  Secret locations are identified using the convention /<vault-secret-path>/<secret-key>

  • enables progressive implementation due to transparency of secret sourcing. Subsequent steps continue to rely on expected environment vars
  • enables use in any toolchain that supports use of environment variables to pass information to application environment. 
  • CICD job steps not tied to a specific secrets store. An alternative secrets storage service could be supported by only requiring modification of the secret getter utility.
  • control of whether to source application environment variables from the CICD job directly or from the secrets engine is managed at the CICD job setup level as opposed to requiring CICD job refactoring to switch the content source.
  • continues the 12 Factor App approach of using environment variables to pass context to application environments.

Example Workflow

An example workflow for a CICD job designed to use environment variables for configuring an application.

Assumptions

The following are available in the CICD environment.

  • A job script oriented CICD automation stack that executes job tasks as a series of shell commands, such as GitLab-CI or Jenkins Pipelines.
  • A secrets storage engine with a python API, such as Hashicorp Vault.
  • CICD execution environment includes the get-vault-secrets-by-approle utility script.

Workflow Steps

Add a Vault secret

Add a secret to Vault at the location secret/fake-app/users/fake-users with a key/value entry of password=fake-password

Add a Vault access policy

Add a Vault policy for the CICD job (or set of CICD jobs) that includes ‘read’ access to the secret.

# cicd-fake-app-policy 
path "secret/data/fake-app/users/fake-user" {
    capabilities = ["read"]
}

path "secret/metadata/fake-app/users/fake-user" {
    capabilities = ["list"]
}

Add a Vault appRole

Add a Vault appRole linked to the new policy.  This example specifies a new appRole with an secret-id TTL of 60 days and non-renewable access tokens with a TTL of 5 minutes.  The CICD job uses the access token to read secrets.

vault write auth/approle/role/fake-role \
    secret_id_ttl=1440h \
    token_ttl=5m \
    token_max_ttl=5m \
    policies=cicd-fake-app-policy

Read the Vault approle-id

Retrieve the approle-id of the new appRole taking note of the returned approle-id.

vault read auth/approle/role/fake-role

Add a Vault appRole secret-id

Add a secret-id for the appRole, taking note of the returned secret-id

vault write -f auth/approle/role/fake-role/secret-id

Add CICD Job Steps

In the CICD job definition insert job steps to retrieve secrets values a set variables in the job execution environment. These are the steps to add in a gitlab-ci.yml CICD job.

...
script:
- get-vault-secrets-by-approle > ${VAULT_VAR_FILE}
- source ${VAULT_VAR_FILE} && rm ${VAULT_VAR_FILE}
...

The helper script get-vault-secrets-by-approle could be executed and sourced in a single step, e.g. source $(get-vault-secrets-by-approle).  However, when executed in a single statement all script output is processed by the source command and script error messages don’t get printed and captured in the job logs.  Splitting the read and environment var sourcing into 2 steps aids in troubleshooting.

Add CICD job vars for Vault access

In the CICD job configuration add Vault access environment variables.

VAULT_ADDR=https://vault.example.com:8200
VAULT_ROLE_ID=db02de05-fa39-4855-059b-67221c5c2f63
VAULT_SECRET_ID=6a174c20-f6de-a53c-74d2-6018fcceff64
VAULT_VAR_FILE=/var/tmp/vault-vars.sh

Add CICD job vars for Vault secrets

In the CICD job configuration add environment variables for the items to be sourced from vault secrets.  The secret path follows the convention of <secret-mount-path>/<secret-path>/<secret-key>

V_FAKE_PASSWORD=secret/fake-app/users/fake-user/password

Remove CICD job vars

In the CICD job configuration remove the previously used FAKE_APP_PASSWORD variable.

Execute the CICD job

Kick off the CICD job.  Any CICD job configuration variables prefixed with “V_” results in the addition of a corresponding environment variable in the job execution environment with content sourced from Vault.

Full source code can be found at:

https://github.com/datwiz/cicd-secrets-in-vault