Helm Ansible Template Exporter

Helm Ansible Template Exporter is a set of tools aimed at helping K8S application developers transition from Helm to Ansible Role Based Operators. This project is separated into two main tools:

1. Helm To Ansible Exporter
2. Ansible Operator Builder

The Ansible Operator Builder is targeted towards developer usage, and is located in the hack directory.

Helm To Ansible Exporter

This tool automates conversion from Helm Chart to Ansible Playbook Role. Helm Charts are defined utilizing Go Template Language, and Ansible Playbook Roles are defined using Yaml and Jinja2 Template Language. Due to the fact that Go Template Language and Jinja2 Template Language are completely separate languages, some facets of Helm charts are difficult or impossible to convert automatically. This tool performs a best attempt conversion of a Helm chart into an Ansible Playbook Role, but some aspects of the conversion process must be performed manually by hand after utilizing this tool. Additionally, when ambiguities in conversion arise, this tool makes a best attempt to emit warnings where a manual conversion or inspection is needed after running the tool.

The output of this tool is an Ansible Role which can be installed using Ansible Playbook, or built into an operator using the Ansible Operator Builder.

Helm To Ansible Exporter Current Capabilities

The current offering does the following:

1. Creates a role in the workspace directory using ansible-galaxy.
2. Raw copies templates into the generated Ansible Playbook Role templates directory, renaming each template with a ".j2" extension.
3. Merges values.yml (or values.yaml) into the generated Ansible Playbook Role defaults/main.yml file.
4. Searches the generated Ansible Playbook Role's defaults/main.yml file for self references (i.e., references to .Values.) and comments them out. Ansible Playbook is incapable of expressing self references in defaults/main.yml, a clear technology gap between Ansible Playbook and Helm charts. A "WARN" message is output indicating that a manual change is required to defaults/main.yml on the appropriate lines.
5. Convert Branch syntax for if, range <list> and range <map> in each template to utilize proper Jinja2 syntax. This includes a heuristic which attempts to determine if conditionals are checking for definition v.s. boolean evaluation.
6. Convert boolean composition ordering. Go Templating utilizes "and " format. On the other hand, Jinja2 utilizes " and " formatting. helmExport handles this conversion automatically.
7. Template functions invocations are converted to Jinja2 Ansible Filter invocations. This requires converting direct function invocations to piped invocations, as well as inserting the appropriate parentheses and commas for argument lists.
8. Removes references to ".Values." in the generated Ansible Playbook's Roles' templates. Ansible Playbook can directly reference the values in defaults/main.yml, so this reference isn't needed.
9. If the "generateFilters" flag is set to true, some stub Ansible Filter implementations are installed for use in converting Go template functions to Ansible Playbook Filters.
10. If the "emitKeysSnakeCase" flag is set to true (default), all Ansible keys are converted to snake_case. This option is especially useful if you plan to generate a K8S operator, since the operator-sdk converts Custom Resource variables to snake_case. This tool directly invokes the ToSnake provided by operator-sdk in an attempt to exactly match the conversion functionality.

Helm To Ansible Exporter Known Limitations

Go/Sprig Template Function Limitations

Ansible Playbook Filter(s) are one candidate to replace Go/Sprig Template Functions. However, they are not a direct 1:1 mapping, so a few extra steps must be taken after conversion.

Implement or Replace Template Function Invocations with Ansible Filters

There are a number of Ansible Playbook Filters built directly into Ansible. For instances where there does not seem to be a replacement, you will need to create your own replacement. If you utilize the "generateFilters" command line argument, some example filters will be installed into your generated Ansible Playbook Role.

"template" and "include" are not supported

Go Templates provide "template" and "include" in order to support dynamic template creation. Ansible has no direct replacement, and although there are some similar constructs, helmExport currently doesn't support any conversion. Instead, consider using Ansible defaults as a replacement.

Building The Exporter

To build the code, use the following command:

make

To clean the code base, use the following command:

make clean

Running the Exporter

Runtime Dependencies

Helm Ansible Template Exporter requires ansible-galaxy to initialize exported roles. At a minimum, we suggest using Ansible Galaxy version 2.9.6. Additionally, ansible-galaxy must be included in your $PATH.

If you utilize the -generateFilters flag, then a GoLang 1.14 compiler must be installed.

Run Instructions

make run

This will run the current implementation of code.

Alternatively:

./helmExport export nginx --helm-chart=./example --workspace=./workspace --generateFilters=true --emitKeysSnakeCase=true

Testing the Ansible Playbook Role

Ansible Operators are deployed using the k8s Ansible Module. The k8s Ansible Module allows developers to leverage existing Kubernetes resource YAML files, and express lifecycle management in native Ansible. One benefit of using Ansible in conjunction with existing Kubernetes resource files is the ability to use Jinja2 templating to customize deployments.

Installing the k8s Ansible Module

The k8s Ansible Module requires Ansible. To install on Fedora/CentOS:

sudo dnf install ansible

The OpenShift Restclient Python package is also required. Install using pip:

pip3 install openshift

Lastly, the Ansible Kubernetes collection is required. Install using ansible-galaxy:

ansible-galaxy collection install community.kubernetes

Testing the Ansible Playbook Role Using the k8s Ansible Module

1. Start a K8S cluster. For example, using minikube:

minikube start

2. Create an Ansible Playbook called workspace/role/playbook.yaml.

---
- hosts: localhost
  roles:
  - Foo

3. Debug any issues not covered by the Helm Ansible Template Exporter by running this diagnostic command:

ansible-playbook playbook.yaml -vvv

Known Test Environments

This tool has been tested using:

• Fedora 31
• macOS Catalina Version 10.15.4