lambda-generic-microservice

AWS Lambda microservice for CRUD on any dynamoDB objects. Can (and probably should) be paired with an AWS API Gateway.

Lambda Usage

You may use this Lambda as is sending custom events with operation types of create, read, update, and delete. The event must contain a hash key as configured in the config.js Only event keys in the config.keys list will be processed on create/update. Create and update are friendly (each is PATCH secretly) and do not require a full object to complete successfully.

Example Events and Response

create

event
{
  "operation": "create",
  "mykey": "ZZZZZZZZZZZZZZZZZ",
  "body": {}
}

response
{
  "statusCode": 201,
  "status": "Created",
  "data": {
    "mykey": "ZZZZZZZZZZZZZZZZZ",
    "location": "unknown",
    "cost": 0
  }
}

read

event
{
  "operation": "read",
  "mykey": "ZZZZZZZZZZZZZZZZZ"
}

response
{
  "statusCode": 200,
  "status": "Ok",
  "data": {
    "mykey": "ZZZZZZZZZZZZZZZZZ",
    "location": "unknown",
    "cost": 0
  }
}

update

event
{
  "operation": "update",
  "mykey": "ZZZZZZZZZZZZZZZZZ",
  "body": {
    "location":"taco bell"
  }
}

response
{
  "statusCode": 200,
  "status": "Ok",
  "data": {
    "mykey": "ZZZZZZZZZZZZZZZZZ",
    "location": "taco bell",
    "cost": 0
  }
}

delete

event
{
  "operation": "delete",
  "mykey": "ZZZZZZZZZZZZZZZZZ"
}

response
{
  "statusCode": 200,
  "status": "OK",
  "data": {}
}

Exceptions and Errors

The Lambda function will return errors with the following format, designed to be regex-able by AWS API Gateway to turn into a matching HttpStatus and formated response object. For example a double create will return "Conflict" so that the API Gateway can map this to HttpStatus and HttpStatusCode Conflict - 409.

{  "errorMessage": "<Http Status Text> : <Lambda error message>" }
eg.
{  "errorMessage": "Conflict : ConditionalCheckFailedException: The conditional request failed" }

Configuration

index.js is agnostic to the data in the object and dynamoDB. This code will work against any table or hash keys as declared in the config.js file.

• table : dynamoDB table name
• keyName : name of hash key in the dynamoDB
• keys : valid hash keys for this dynamoDB table
• defaultCreate : default values for new records

eg.

config = {
  region: 'us-east-1',
  table: 'Lunch',
  keyName: 'mykey',
  keys: ['cost', 'location'],
  defaultCreate: {
    mykey: null,
    location: "unknown",
    cost: 0
  }
}

Using with API Gateway

To make this into a more friendly REST API you can setup GET/POST/PUT/DELETE methods in an API Gateway.

Request mapping

Using integration request methods to map url or query params into the event object passed to Lambda.

Examples:

request - GET - /<api host>/<api stage>/lunch/:mykey

// mapper in API Gateway
{ "operation":"read", "mykey":"$input.params('mykey')" }  

// example event passed to lambda  
{ "operation":"read", "mykey":"123456789101212" }  

request POST - /<api host>/<api stage>/lunch/:mykey body

// mapper in API Gateway
{ "operation":"create", "mykey":"$input.params('mykey')", "body":$input.json('$') }

// exaple event passed to lambda
{
  "operation":"create",
  "mykey":"123456789101212",
  "body": {
    location: "desk",
    cost: 0,
  }
}

Response mapping

Using integration response methods you can map error messages and responses from the lambda to appropriate HttpStatus codes and messages.

Example (error response):

//response from lambda  
{  "errorMessage": "Conflict : ConditionalCheckFailedException: The conditional request failed" }

//regex rule in API Gateway response integration mapping  
Conflict.*

//mapper in API Gateway
{ "status" : "CONFLICT", "errorMessage": "$input.path('errorMessage')", "statusCode":409 }

//response from API Gateway  
application/json  
409  
{ "status" : "CONFLICT",
  "errorMessage": "Conflict : ConditionalCheckFailedException: The conditional request failed",
  "statusCode":409
}

Deployment

The deploy directory contains shell scripts to create and upload a Lambda function as well as set policy on it. AWS cli installation and properly configured aws credentials on a must for this shell to work.

No CLI exists for API gateway at this time.

Needed/Potential Improvements

• Lambda should just return object on success, let the gateway map to a success object.
• some real tests?
• once aws-cli has api gateway commands, make a full create/teardown script so people can quickly play with this
• consider being stricter about PATCH/PUT/POST?

Reference

AWS Lambda Documentation AWS API Gateway AWS DyanmoDB

This is very much based on the http-microservice lambda example titled "microservice-http-endpoint" provided by AWS. Their blueprint as of writing this README was the old dynamodb-doc node package instead of the AWS stated preferred usage of AWS.DynamoDB.DocumentClient in the regular aws-sdk for node. I followed this update and did not use dynamodb-doc. Read more here