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Version: 1.43.0

Use Stackables to build Platformatic applications

Platformatic Service and Platformatic DB offer a good starting point to create new applications. However, most developers or organizations might want to create reusable services or applications built on top of Platformatic. We call these reusable services "Stackables" because you can create an application by stacking services on top of them.

This is useful to publish the application on the public npm registry (or a private one!), including building your own CLI, or to create a specialized template for your organization to allow for centralized bugfixes and updates.

This process is the same one we use to maintain Platformatic DB and Platformatic Composer on top of Platformatic Service.

Creating a custom Service

To create a custom Platformatic Stackable you can use the create-platformatic CLI command:

npx create-platformatic@latest
  • What kind of project do you want to create?
    • Stackable
  • Where would you like to create your project?
    • .
  • What is the name of the stackable?
    • my-stackable
  • Do you want to use TypeScript?
    • no
  • Do you want to init the git repository?
    • no

After installing the dependencies, let's take a look at the project structure:

.
├── cli
│ ├── create.js
│ └── index.js
├── lib
│ ├── generator.js
│ └── schema.js
├── plugins
│ └── example.js
├── config.d.ts
├── index.d.ts
├── index.js
└── package.json

Stackable plugin

index.js is the entry point of the Stackable. It exports a custom stackable function with all required information to be used by Platformatic Service. stackable is a fastify plugin so you can register any custom plugins, routes, hooks in it.

async function stackable (fastify, opts) {
await fastify.register(platformaticService, opts)
await fastify.register(require('./plugins/example'), opts)
}

platformaticService is used here as a base for the Stackable. In the same way, you can use platformaticDB, platformaticComposer or even skip it if you want to create a custom Stackable from scratch.

Each Stackable should have a few required properties attached to the stackable function:

  • stackable.configType: The name of the Stackable.
  • stackable.schema: The JSON schema of the Stackable config.
  • stackable.generator: a class extending BaseGenerator or any other stackable generator. Used to generate the Stackable application.
  • stackable.configManagerConfig: ab object with the config for the ConfigManager class. Used to manage the Stackable config.
stackable.configType = 'my-stackable-app'
stackable.schema = schema
stackable.Generator = Generator
stackable.configManagerConfig = {
schema,
allowToWatch: ['.env'],
schemaOptions: {
useDefaults: true,
coerceTypes: true,
allErrors: true,
strict: false
},
transformConfig: async () => {}
}

Stackable generator

MyStackableGenerator is a class extending BaseGenerator or any other stackable generator (ServiceGenerator in this example). It's used to generate a Stackable application. You can find an example of a generator in lib/generator.js.

'use strict'

const { Generator: ServiceGenerator } = require('@platformatic/service')
const { schema } = require('./schema')

class MyStackableGenerator extends ServiceGenerator {
getDefaultConfig () {
const defaultBaseConfig = super.getDefaultConfig()
const defaultConfig = {
greeting: 'Hello world!'
}
return Object.assign({}, defaultBaseConfig, defaultConfig)
}

async _getConfigFileContents () {
const baseConfig = await super._getConfigFileContents()
const config = {
$schema: './stackable.schema.json',
greeting: {
text: '{PLT_GREETING_TEXT}'
}
}
return Object.assign({}, baseConfig, config)
}

async _beforePrepare () {
super._beforePrepare()

this.config.env = {
PLT_GREETING_TEXT: this.config.greeting ?? 'Hello world!',
...this.config.env
}
}

async _afterPrepare () {
this.addFile({
path: '',
file: 'stackable.schema.json',
contents: JSON.stringify(schema, null, 2)
})
}
}

module.exports = MyStackableGenerator
module.exports.Generator = MyStackableGenerator

This generator extends ServiceGenerator which means it will generate an application based on Platformatic Service. If you want to create a Stackable based on Platformatic DB or Platformatic Composer you can extend DBGenerator or ComposerGenerator respectively.

In addition this generator adds a custom greeting property to the Stackable config and generates a stackable.schema.json file with the JSON schema of the Stackable config. Greeting text will be taken from the PLT_GREETING_TEXT environment variable. Generator will create a .env file with the PLT_GREETING_TEXT variable set to Hello world! by default.

Stackable schema

schema is the JSON schema of the Stackable config. It's used to validate the Stackable config. You can find an example of a schema in lib/schema.js.

'use strict'

const { schema } = require('@platformatic/service')

const myStackableSchema = {
...schema.schema,
$id: 'my-stackable',
title: 'My Stackable Config',
properties: {
...schema.schema.properties,
greeting: {
type: 'object',
properties: {
text: {
type: 'string'
}
},
required: ['text'],
additionalProperties: false
}
}
}

module.exports.schema = myStackableSchema

if (require.main === module) {
console.log(JSON.stringify(myStackableSchema, null, 2))
}

This schema extends the Platformatic Service schema and adds a custom greeting property. You can also use the stackable schema to generate a types file for the Stackable config. To do so, you can use npm run build:config cli command.

Note that the $id property of the schema identifies the module in our system, allowing us to retrieve the schema correctly. When your stackable is ready you can publish the config schema and use a remote schema url instead. It is recommended, but not required, that the JSON schema is actually published in this location. Doing so allows tooling such as the VSCode language server to provide autocompletion.

Example

{
"$id": "https://example.com/schemas/my-stackable.schema.json"
}

### Stackable CLI

If you chose to use TypeScript, you will need to run `npm run build` first to compile the Stackable.

You can find two scripts in the `cli` folder: `create.js` and `start.js`. These scripts are used to create and start a Stackable application respectively. `package.json` contains two bin commands: `create-my-stackable` and `start-my-stackable` which are used to run these scripts. Note that CLI commands include the Stackable name, so it might be different if you chose a different name for your Stackable.

```json
{
"bin": {
"create-my-stackable": "./cli/create.js",
"start-my-stackable": "./cli/start.js"
}
}

To use these commands before publishing the Stackable to npm you can run npm link in the Stackable folder. This will create symlinks to the Stackable scripts in the global folder. After that you can use create-my-stackable and start-my-stackable commands in any folder.

npm link

Creating a Stackable application

If you chose to use TypeScript, you will need to run npm run build first to compile the Stackable.

To create an application based on your Stackable you can run the create-my-stackable cli command. This command uses the cli/create.js script to generate the application. By default application will be generated in a ./my-stackable-app folder. To change the default folder you can use the --dir option. For other options check the cli/create.js script.

After generating the application you can find a stackable app config file ./app/platformatic.json with the custom greeting option. Option value is set in a .env file as a PLT_GREETING_TEXT environment variable.

{
"$schema": "./stackable.schema.json",
"server": {
"hostname": "{PLT_SERVER_HOSTNAME}",
"port": "{PORT}",
"logger": {
"level": "{PLT_SERVER_LOGGER_LEVEL}"
}
},
"service": {
"openapi": true
},
"watch": true,
"plugins": {
"paths": [
{
"path": "./plugins",
"encapsulate": false
},
"./routes"
]
},
"greeting": {
"text": "{PLT_GREETING_TEXT}"
}
}

You can see that the config uses the local ./stackable.schema.json file to validate the config. When your stackable is ready you can publish the config schema and use a remote schema url instead.

Example

{
"$schema": "https://example.com/schemas/my-stackable.schema.json"
}

Starting a Stackable application

To start the application you can run the start-my-stackable cli command. This command uses the cli/start.js script to start the application. By default start-my-stackable looks for a project in the current folder. To change the default folder you can use the -c option to specify a path to the platformatic.json file.

In the logs you should see the custom greeting logged from the stackable ./plugins/example.js plugin.

[12:27:10.724] INFO (87553): Loading stackable greeting plugin.
greeting: {
"text": "Hello world!"
}
[12:27:10.730] INFO (87553): Server listening at http://0.0.0.0:3042