Serverless fragments

A node.js template processor for creating reusable serverless fragments.

The engine loads a specified top-level yaml file recursively and resolves template placeholders.

A top level file as well as nested files do not need to be valid yaml objects, only the final structure, after the processing is done, has to be. This allows a flexibility to define partial yaml arrays or objects which can be merged into a parent file.

The final yaml object is loaded using js-yaml

Loaded yaml object can be thus exported and processed by serverless framework:

module.exports = slsFragments.load(path.join(__dirname, 'serverless/serverless.core.yml', new Map[['version':'1.0.1']]));

Parameters including process arguments passed to serverless are passed recursively to child fragments loaded by tfile.

Placeholders

tfile

Loads the specified file recursively and apply parameters to matched variables names specified using opt, and custom placeholders.

Avoid using the following reserved characters for:

• file names } :

• parameters names and values , =

tfile supports referencing json files, which are automatically converted to yaml if their extension is .json This might be useful to keep configuration files as json and easily reuse them with the code, as many languages support JSON natively, unlike yaml.

 config
 ├── local.json
 └── dev.json
 └── test.json
 └── stage.json
 └── prod.json

 custom:
   ${tfile:config/${opt:stage}.json}

tfile supports file resolution using a list of relative paths, which can be provided to the engine. This can be useful when referencing fragments from another npm modules. E.g.

module.exports = slsFragments.load(path.join(__dirname, 'serverless/serverless.core.yml', new Map()), ['../node_modules/serverless-constructs/']);

The engine will try to resolve tfile file reference as follows:

[project dir]/[tfile file path]
[project dir]/[relative dir 1]/[tfile file path]
[project dir]/[relative dir 2]/[tfile file path]

Syntax: tfile:[file path]:[parameters], where

• file_ a relative path to nested template file (relative to the directory of the loaded top level file)

• parameters comma separated name-value pairs of parameters to replace opt and custom placeholders in the nested template file

Usage:

• nested file without parameters ${tfile:iamRoleStatements/dynamoDbFull.yml}

• with parameters ${tfile:iamRoleStatements/dynamoDbFull.yml:tableName=entity}

• multiline declaration

 ${tfile:resources/sqsQueue.yml:
    visibilityTimeout=60,
    delaySeconds=10
 }

Note: tfile supports an optional colon after the declaration which is removed once there are resolved by the engine. The reason for it is to avoid validation error by yaml formatter in VSCode which otherwise reports the lines with tokens only as invalid mapping entry. This is a valid syntax too ${tfile:config/${opt:stage}.json}:

opt and custom

Variables names specified using these placeholders are replaced with parameters passed from template#load function in top level file or tfile in nested templates

Syntax: opt:[variable name], [default value] or custom:[variable name], [default value], where

• variable name_ is matched against parameter names

• default value and the comma before it is optional. If provided the value will be used if there is no matching parameter. Compare to serverless defaults, also numeric values are supported

Usage:

• a serverless command line opt parameter ${opt:stage}

• a serverless custom variables ${self:service.name}

• multiple variables on a single line ${self:service.name}-${opt:stage}

• nested variables ${self:${opt:env}.tableName}

• a variables with a default ${opt:stage, 'test'}

Comments

Use # for line comments, anything between the # and end of line will be skipped from processing

Usage:

• comment out fragments # ${tfile:iamRoleStatements/dynamoDbFull.yml:tableName=entity}

• add comments to the fragments# full entity table and all it's indexes access for the lambda

Examples

├── package.json
├── serverless.js
├── serverless
│   ├── serverless.core.yml
│   ├── provider
│   │   └── nodejs.yml
│   ├── resources
│   │   └── sqsQueue.yml

package.json

  "devDependencies": {
    "serverless-fragments": "^2.6.0"
   }

serverless.js

const path = require('path');
const slsFragments = require('serverless-fragments');

module.exports = slsFragments.load(path.join(__dirname, 'serverless/serverless.core.yml', new Map([['version', '1.0.0']])));

serverless.core.yml

# entityService AWS serices definition 
service: entityService

provider:
  ${tfile:provider/nodejs.yml}
  environment:
    ENV: ${self:provider.stage}
    VERSION: ${opt:version}

functions:
  createEntity:
    handler: dist/src/entityRestHandler.create
    events:
    - http:
        path: /entity
        method: post

resources:
  Resources:
    ${tfile:resources/sqsQueue.yml:queueName=entity}

provider/nodejs.yml

name: aws
runtime: nodejs8.10
stage: ${opt:stage, 'dev'}
region: ${opt:region, 'ap-southeast-2'}
memorySize: 512

resources/sqsQueue.yml

${opt:queueName}Queue:
  Type: "AWS::SQS::Queue"
  Properties:
    QueueName: ${opt:queueName}Queue

Use standard serverless command to use the serverless.js file e.g.

sls package --stage dev --region ap-southeast-2 -v

Changelog

• 1.0.5 supports comments - # at the beginning of a line (with optional lead white spaces) will skip the line from processing
• 1.0.1 added support to match and resolve nested variables like ${self:custom.tableName${opt:env}}
• 1.1.0 tfile supports referencing json files, which are automatically converted to yaml if their extension is. json
• 1.2.1 opt and custom now match variable names with defaults e.g. ${opt:stage, 'dev'}
• 2.0.0 rename to Serverless Fragments
  • process default variable values
  • support multiline tfile declaration
• 2.1.0 pass parameters to fragments recursively
• 2.6.0 support a list of relative paths for tfile lookup