cowsay

README

A Porter Mixin Skeleton

This repository contains the skeleton structure of a Porter Mixin. You can clone this repository and use it as a starting point to build new mixins. The structure of this project matches closely with existing Porter Mixins.

1. Create a new repository in GitHub using this repository as a template.
2. Clone your new repository following the usual Go conventions. If you are using Go 1.11, clone it into your GOPATH such as ~/go/src/github.com/YOURNAME/YOURMIXIN. If you are using Go 1.12+ with go modules, you may chose to clone it outside of the GOPATH.
3. Rename the cmd/cowsay and pkg/cowsay directories to cmd/YOURMIXIN and pkg/YOURMIXIN.
4. Rename pkg/YOURMIXIN/schema/schema
5. Find the text github.com/deislabs/porter-cowsay/pkg/cowsay in the repository and change it to github.com/YOURNAME/YOURREPO/pkg/YOURMIXIN.
6. Find any remaining cowsay text in the repository and replace it with YOURMIXIN.
7. Run dep ensure. Check-in Gopkg.lock and vendor.
8. Run make build xbuild test to try out all the make targets and verify that everything executes without failing.
9. Run make install to install your mixin into the Porter home directory. If you don't already have Porter installed, install it first.
10. Now your mixin is installed, you are ready start customizing and iterating on your mixin!

Customize your mixin

This mixin is ready to wrap an existing command-line tool. The shortest path would be to edit build.go to add the instructions to download the tool and you are all set. It will look and feel like the gcloud or aws mixins, both of which are built on top of the exec mixin.

Edit the Build function in pkg/cowsay/build.go. Here you can add any Dockerfile lines that you require to download and install additional tools, configuration files, etc necessary for your mixin. The Build function should write the Dockerfile lines to m.Out which is a pipe from the mixin back to porter.

Search for TODO in the code and follow the instructions to customize the mixin.

Here is an example from the aws mixin, where it downloads the latest version of of the aws binary and installs it:

https://github.com/deislabs/porter-aws/blob/001c19bfe06d248143353a55f07a42c913579481/pkg/aws/build.go#L7

This is enough to have a working mixin. Run make build install and then test it out with a bundle.

That will get you started but make sure to read the mixin developer documentation for how to create a full featured mixin:

• Mixin Architecture
• Mixin Commands
• Distributing Mixins

Project Structure

In the cmd/cowsay directory, you will find a cli built using spf13/cobra. The CLI contains a go file for each basic capability a Mixin should implement:

• build
• schema
• version
• install
• upgrade
• invoke
• uninstall

Each of these command implementations have a corresponding Mixin implementation in the pkg/cowsay directory. Each of the commands above is wired into an empty implementation in pkg/cowsay that needs to be completed. In order to build a new Mixin, you need to complete these implementations with the relevant technology. For example, to build a Cloud Formation mixin, you might implement the methods in pkg/cowsay using the AWS Go SDK.

Provided capabilities

This skeleton mixin project brings some free capabilities:

File System Access and Context

Porter provides a Context package that has helpful mechanisms for accessing the File System using spf13/afero. This makes it easy to provide mock File System implementations during testing. The Context package also provides a mechanism to encapsualte stdin, stdout and stderr so that they can easily be passed from cmd/cowsay code to implementing pkg/cowsay code.

Template and Static Asset Handling

The project already includes Packr V2 for dealing with static files, such as templates or other content that is best modeled outside of a Go file. You can see an example of this in pkg/cowsay/schema.go.

Basic Schema

The project provides an implementation of the cowsay schema command that is mostly functional. To fully implement this for your mixin, you simply need to provide a valid JSON schema. For reference, consult pkg/cowsay/schema/schema.json.

Basic Tests

The project provides some very basic test skeletons that you can use as a starting point for building tests for your mixin.

Makefile

The project also includes a Makefile that will can be used to both build and install the mixin. The Makefile also includes a TODO publish target that shows how you might publish the mixin and generate an mixin feed for easily sharing your mixin.