Plugins

A Plugin is custom Javascript code that creates new or extends existing commands within the Serverless Framework. The Serverless Framework is merely a group of Plugins that are provided in the core. If you or your organization have a specific workflow, install a pre-written Plugin or write a plugin to customize the Framework to your needs. External Plugins are written exactly the same way as the core Plugins.

Installing Plugins

External Plugins are added on a per service basis and are not applied globally. Make sure you are in your Service's root directory, then install the corresponding Plugin with the help of NPM:

npm install --save custom-serverless-plugin

We need to tell Serverless that we want to use the plugin inside our service. We do this by adding the name of the Plugin to the plugins section in the serverless.yml file.

# serverless.yml file

plugins:
  - custom-serverless-plugin

The plugins section supports two formats:

Array object:

plugins:
  - plugin1
  - plugin2

Enhanced plugins object:

plugins:
  localPath: './custom_serverless_plugins'
  modules:
    - plugin1
    - plugin2

Plugins might want to add extra information which should be accessible to Serverless. The custom section in the serverless.yml file is the place where you can add necessary configurations for your plugins (the plugins author / documentation will tell you if you need to add anything there):

plugins:
  - custom-serverless-plugin

custom:
  customkey: customvalue

Service local plugin

If you are working on a plugin or have a plugin that is just designed for one project, it can be loaded from the local .serverless_plugins folder at the root of your service. Local plugins can be added in the plugins array in serverless.yml.

plugins:
  - custom-serverless-plugin

Local plugins folder can be changed by enhancing plugins object:

plugins:
  localPath: './custom_serverless_plugins'
  modules:
    - custom-serverless-plugin

The custom-serverless-plugin will be loaded from the custom_serverless_plugins directory at the root of your service. If the localPath is not provided or empty, the .serverless_plugins directory will be used.

The plugin will be loaded based on being named custom-serverless-plugin.js or custom-serverless-plugin\index.js in the root of localPath folder (.serverless_plugins by default).

If you want to load a plugin from a specific directory without affecting other plugins, you can also specify a path relative to the root of your service:

plugins:
  # This plugin will be loaded from the `.serverless_plugins/` or `node_modules/` directories
  - custom-serverless-plugin
  # This plugin will be loaded from the `sub/directory/` directory
  - ./sub/directory/another-custom-plugin

Load Order

Keep in mind that the order you define your plugins matters. When Serverless loads all the core plugins and then the custom plugins in the order you've defined them.

# serverless.yml

plugins:
  - plugin1
  - plugin2

In this case plugin1 is loaded before plugin2.

Writing Plugins

Note: In order to ensure that your plugin works correctly with Framework in v2.x, keep the following things in mind:

  • Do not depend on Bluebird API for Promises returned by Framework internals - we are actively migrating away from Bluebird at this point
  • If your plugin adds new properties, ensure to define corresponding schema definitions, please refer to: Extending validation schema
  • Avoid using subcommands as the support for them might become deprecated or removed in next major version of the Framework
  • Add serverless to peerDependencies in order to ensure officially supported Framework version(s)

Concepts

Plugin

Code which defines Commands, any Events within a Command, and any Hooks assigned to a Lifecycle Event.

  • Command // CLI configuration, commands, options
    • LifecycleEvent(s) // Events that happen sequentially when the command is run
      • Hook(s) // Code that runs when a Lifecycle Event happens during a Command

Command

A CLI Command that can be called by a user, e.g. serverless foo. A Command has no logic, but simply defines the CLI configuration (e.g. command, parameters) and the Lifecycle Events for the command. Every command defines its own lifecycle events.

'use strict';

class MyPlugin {
  constructor() {
    this.commands = {
      foo: {
        lifecycleEvents: ['resources', 'functions'],
      },
    };
  }
}

module.exports = MyPlugin;

Lifecycle Events

Events that fire sequentially during a Command. The above example lists two Events. However, for each Event, an additional before and after event is created. Therefore, six Events exist in the above example:

  • before:foo:resources
  • foo:resources
  • after:foo:resources
  • before:foo:functions
  • foo:functions
  • after:foo:functions

The name of the command in front of lifecycle events when they are used for Hooks.

Hooks

A Hook binds code to any lifecycle event from any command.

'use strict';

class MyPlugin {
  constructor() {
    this.commands = {
      foo: {
        lifecycleEvents: ['resources', 'functions'],
      },
    };

    this.hooks = {
      'before:foo:resources': this.beforeFooResources,
      'foo:resources': this.fooResources,
      'after:foo:functions': this.afterFooFunctions,
    };
  }

  beforeFooResources() {
    console.log('Before Foo Resources');
  }

  fooResources() {
    console.log('Foo Resources');
  }

  afterFooFunctions() {
    console.log('After Foo Functions');
  }
}

module.exports = MyPlugin;

Custom Variable Types

Plugins may register its own configuration variables resolution sources.

Resolvers should be configured at configurationVariablesSources in form of a plain object that exposes resolve function. Check below example

'use strict';

class SomePlugin {
  constructor() {

    this.configurationVariablesSources = {
      foo: {
        async resolve({ address, params, resolveConfigurationProperty, options  }) {
          // `address` and `params` reflect values configured with a variable:
          // ${foo(param1, param2):address}
          // Note: they're passed if they're configured into variable

          // `options` is CLI options
          // `resolveConfigurationProperty` allows to access other configuration properties,
          // and guarantees to return a fully resolved form (even if property is configured with variables)
          const stage = options.stage || await  resolveConfigurationProperty(["provider", "stage"]) || "dev";

          // Resolver is expected to return plain object, with resolved value set on `value` property.
          // Resolve value can be any JSON value
          return {
            //
            value: `Resolution of "foo" source for "${stage}" stage at "${address || ""}" addresss with "${(params || []).join(", ")}" params`
          }
        }
      }

}

Having an above source resolver (as provided with a plugin), we may use new variable source in configuration as follows:

service: test
provider: aws
custom:
  value1: ${foo(one, two):whatever}
plugins:
  - ./some-plugin

Configuration will be resolved into following form:

service: test
provider: aws
custom:
  value1: Resolution of "foo" source for "dev" stage at "whatever" address with "one, two" params
plugins:
  - ./some-plugin

Defining Options

Each command can have multiple Options.

Options are passed in with a double dash (--) like this: serverless foo --function functionName.

Option Shortcuts are passed in with a single dash (-) like this: serverless foo -f functionName.

The options object will be passed in as the second parameter to the constructor of your plugin.

In it, you can optionally add a shortcut property, as well as a required property. The Framework will return an error if a required Option is not included. You can also set a default property if your option is not required.

Additionally type for each option should be set. Supported types are string, boolean and multiple (multiple strings).

Note: At this time, the Serverless Framework does not use parameters.

'use strict';

class MyPlugin {
  constructor(serverless, options) {
    this.serverless = serverless;
    this.options = options;

    this.commands = {
      foo: {
        lifecycleEvents: ['functions'],
        options: {
          function: {
            usage: 'Specify the function you want to handle (e.g. "--function myFunction")',
            shortcut: 'f',
            required: true,
            type: 'string', // Possible options: "string", "boolean", "multiple"
          },
        },
      },
    };

    this.hooks = {
      'foo:functions': this.fooFunction.bind(this),
    };
  }

  fooFunction() {
    console.log('Foo function: ', this.options.function);
  }
}

module.exports = MyPlugin;

Provider Specific Plugins

Plugins can be provider specific which means that they are bound to a provider.

Note: Binding a plugin to a provider is optional. Serverless will always consider your plugin if you don't specify a provider.

The provider definition should be added inside the plugins constructor:

'use strict';

class ProviderX {
  constructor(serverless, options) {
    this.serverless = serverless;
    this.options = options;

    // set the providers name here
    this.provider = this.serverless.getProvider('providerX');

    this.commands = {
      foo: {
        lifecycleEvents: ['functions'],
        options: {
          function: {
            usage: 'Specify the function you want to handle (e.g. "--function myFunction")',
            required: true,
            type: 'string', // Possible options: "string", "boolean", "multiple"
          },
        },
      },
    };

    this.hooks = {
      'foo:functions': this.fooFunction.bind(this),
    };
  }

  fooFunction() {
    console.log('Foo function: ', this.options.function);
  }
}

module.exports = ProviderX;

The Plugin's functionality will now only be executed when the Serverless Service's provider matches the provider name which is defined inside the plugins constructor.

Serverless Instance

The serverless instance which enables access to global service config during runtime is passed in as the first parameter to the plugin constructor.

'use strict';

class MyPlugin {
  constructor(serverless, options) {
    this.serverless = serverless;
    this.options = options;

    this.commands = {
      log: {
        lifecycleEvents: ['serverless'],
      },
    };

    this.hooks = {
      'log:serverless': this.logServerless.bind(this),
    };
  }

  logServerless() {
    console.log('Serverless instance: ', this.serverless);
  }
}

module.exports = MyPlugin;

Note: Variable references in the serverless instance are not resolved before a Plugin's constructor is called, so if you need these, make sure to wait to access those from your hooks.

Command Naming

Command names need to be unique. If we load two commands and both want to specify the same command (e.g. we have an integrated command deploy and an external command also wants to use deploy) the Serverless CLI will print an error and exit. If you want to have your own deploy command you need to name it something different like myCompanyDeploy so they don't clash with existing plugins.

Extending validation schema

If your plugin adds support for additional params in serverless.yml file, you should also add validation rules to the Framework's schema. Otherwise, the Framework may place validation errors to command output about your params.

The Framework uses JSON-schema validation backed by AJV. You can extend initial schema inside your plugin constuctor by using defineTopLevelProperty, defineCustomProperties, defineFunctionEvent, defineFunctionEventProperties, defineFunctionProperties or defineProvider helpers.

Use the following map to know which helper suits best your needs.

custom:
  my-plugin:
    customProperty: foobar # <-- use defineCustomProperties

my-plugin: # <-- use defineTopLevelProperty
  customProperty: foobar

provider:
  name: new-provider # <-- use defineProvider
  my-plugin:
    customProperty: foobar

functions:
  someFunc:
    handler: handler.main
    customProperty: foobar # <-- use defineFunctionProperties
    events:
      - yourPluginEvent: # <-- use defineFunctionEvent
          customProperty: foobar
      - http:
          customProperty: foobar # <-- use defineFunctionEventProperties

We'll walk though those helpers. You may also want to check out examples from helpers tests

defineTopLevelProperty helper

If your plugin requires additional top-level properties (like provider, custom, service...), you can use the defineTopLevelProperty helper to add their definition.

Considering the following example

// serverless.yml

service: my-service

yourPlugin:
  someProperty: foobar

you'll need to add validation rules as described below:

class NewTopLevelPropertyPlugin {
  constructor(serverless) {
    this.serverless = serverless;

    // Create schema for your properties. For reference use https://github.com/ajv-validator/ajv
    const newCustomPropSchema = {
      type: 'object',
      properties: {
        someProperty: { type: 'string' },
      },
      required: ['someProperty'],
    };

    // Attach your piece of schema to main schema at top level
    serverless.configSchemaHandler.defineTopLevelProperty('yourPlugin', newCustomPropSchema);
  }
}

This way, if user sets someProperty by mistake to false, the Framework would display an error:

Serverless: Configuration error: yourPlugin.someProperty should be string

defineCustomProperties helper

Let's say your plugin depends on some properties defined in custom section of serverless.yml file.

// serverless.yml

custom:
  yourPlugin:
    someProperty: foobar

To add validation rules to these properties, your plugin would look like this:

class NewEventPlugin {
  constructor(serverless) {
    this.serverless = serverless;

    // Create schema for your properties. For reference use https://github.com/ajv-validator/ajv
    const newCustomPropSchema = {
      type: 'object',
      properties: {
        someProperty: { type: 'string' },
      },
      required: ['someProperty'],
    };

    // Attach your piece of schema to main schema
    serverless.configSchemaHandler.defineCustomProperties(newCustomPropSchema);
  }
}

This way, if user sets someProperty by mistake to false, the Framework would display an error:

Serverless: Configuration error: custom.yourPlugin.someProperty should be string

defineFunctionEvent helper

Let's say your plugin adds support to a new yourPluginEvent function event. To use this event, a user would need to have serverless.yml file like this:

// serverless.yml

functions:
  someFunc:
    handler: handler.main
    events:
      - yourPluginEvent:
          someProp: hello
          anotherProp: 1

In this case your plugin should add validation rules inside your plugin constructor. Otherwise, the Framework would display an error message saying that your event is not supported:

Serverless: Configuration error: Unsupported function event 'yourPluginEvent'

To fix this error and more importantly to provide validation rules for your event, modify your plugin constructor with code like this:

class NewEventPlugin {
  constructor(serverless) {
    this.serverless = serverless;

    // Create schema for your properties. For reference use https://github.com/ajv-validator/ajv
    serverless.configSchemaHandler.defineFunctionEvent('providerName', 'yourPluginEvent', {
      type: 'object',
      properties: {
        someProp: { type: 'string' },
        anotherProp: { type: 'number' },
      },
      required: ['someProp'],
      additionalProperties: false,
    });
  }
}

This way, if user sets anotherProp by mistake to some-string, the Framework would display an error:

Serverless: Configuration error: functions.someFunc.events[0].yourPluginEvent.anotherProp should be number

defineFunctionEventProperties helper

When your plugin extend other plugin events definition for a specific provider, you can use the defineFunctionEventProperties to extend event definition with your custom properties.

For example, if your plugin adds support to a new documentation property on http event from aws provider, you should add validations rules inside your plugin constructor for this new property.

class NewEventPlugin {
  constructor(serverless) {
    this.serverless = serverless;

    // Create schema for your properties. For reference use https://github.com/ajv-validator/ajv
    serverless.configSchemaHandler.defineFunctionEventProperties('aws', 'http', {
      properties: {
        documentation: { type: 'object' },
      },
      required: ['documentation'],
    });
  }
}

This way, if user sets documentation by mistake to anyString, the Framework would display an error:

Serverless: Configuration error: functions.someFunc.events[0].http.documentation should be object

defineFunctionProperties helper

Let's say your plugin adds support to a new someProperty function property. To use this property, a user would need to have serverless.yml file like this:

// serverless.yml

functions:
  someFunc:
    handler: handler.main
    someProperty: my-property-value

In this case your plugin should add validation rules inside your plugin constructor. Otherwise, the Framework would display an error message saying that your property is not supported:

ServerlessError: Configuration error:
at 'functions.someFunc': unrecognized property 'someProperty'

To fix this error and more importantly to provide validation rules for your property, modify your plugin constructor with code like this:

class NewFunctionPropertiesPlugin {
  constructor(serverless) {
    this.serverless = serverless;

    // Create schema for your properties. For reference use https://github.com/ajv-validator/ajv
    serverless.configSchemaHandler.defineFunctionProperties('providerName', {
      properties: {
        someProperty: { type: 'string' },
        anotherProperty: { type: 'number' },
      },
      required: ['someProperty'],
    });
  }
}

This way, if user sets anotherProperty by mistake to hello, the Framework would display an error:

ServerlessError: Configuration error at 'functions.someFunc.anotherProperty': should be number

defineProvider helper

In case your plugin provides support for new provider, you would want to adjust validation schema. Here is example:

class NewProviderPlugin {
  constructor(serverless) {
    this.serverless = serverless;

    // Create schema for your provider. For reference use https://github.com/ajv-validator/ajv
    serverless.configSchemaHandler.defineProvider('newProvider', {
      // Eventual reusable schema definitions (will be put to top level "definitions" object)
      definitions: {
        // ...
      },

      // Top level "provider" properties
      provider: {
        properties: {
          stage: { type: 'string' },
          remoteFunctionData: { type: 'null' },
        },
      },

      // Function level properties
      function: {
        properties: { handler: { type: 'string' } },
      },

      // Function events definitions (can be defined here or via `defineFunctionEvent` helper)
      functionEvents: {
        someEvent: {
          name: 'someEvent',
          schema: {
            type: 'object',
            properties: {
              someRequiredStringProp: { type: 'string' },
              someNumberProp: { type: 'number' },
            },
            required: ['someRequiredStringProp'],
            additionalProperties: false,
          },
        },
      },

      // Definition for eventual top level "resources" section
      resources: {
        type: 'object',
        properties: {
          // ...
        },
      },

      // Definition for eventual top level "layers" section
      layers: {
        type: 'object',
        additionalProperties: {
          type: 'object',
          properties: {
            // ...
          },
        },
      },
    });
  }
}

Extending the info command

The info command which is used to display information about the deployment has detailed lifecycleEvents you can hook into to add and display custom information.

Here's an example overview of the info lifecycle events the AWS implementation exposes:

-> info:info
  -> aws:info:validate
  -> aws:info:gatherData
  -> aws:info:displayServiceInfo
  -> aws:info:displayApiKeys
  -> aws:info:displayEndpoints
  -> aws:info:displayFunctions
  -> aws:info:displayStackOutputs

Here you could e.g. hook into after:aws:info:gatherData and implement your own data collection and display it to the user.

Note: Every provider implements its own info plugin so you might want to take a look into the lifecycleEvents the provider info plugin exposes.

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