Serverless WarmUP Plugin ♨

Keep your lambdas warm during Winter.

Requirements:

Serverless v1.12.x or higher.
AWS provider

How it works

WarmUP solves cold starts by creating one schedule event lambda that invokes all the service lambdas you select in a configured time interval (default: 5 minutes) or a specific time, forcing your containers to stay alive.

Setup

Install via npm in the root of your Serverless service:

npm install serverless-plugin-warmup --save-dev

Add the plugin to the plugins array in your Serverless serverless.yml:

plugins:
  - serverless-plugin-warmup

Add warmup: true property to all functions you want to be warm:

functions:
  hello:
    warmup: true

WarmUP to be able to invoke lambdas requires the following Policy Statement in iamRoleStatements:

iamRoleStatements:
  - Effect: 'Allow'
    Action:
      - 'lambda:InvokeFunction'
    Resource:
    - Fn::Join:
      - ':'
      - - arn:aws:lambda
        - Ref: AWS::Region
        - Ref: AWS::AccountId
        - function:${self:service}-${opt:stage, self:provider.stage}-*

Add an early callback call when the event source is serverless-plugin-warmup. You should do this early exit before running your code logic, it will save your execution duration and cost:

module.exports.lambdaToWarm = function(event, context, callback) {
  /** Immediate response for WarmUP plugin */
  if (event.source === 'serverless-plugin-warmup') {
    console.log('WarmUP - Lambda is warm!')
    return callback(null, 'Lambda is warm!')
  }
  
  ... add lambda logic after
}

All done! WarmUP will run on SLS deploy and package commands

Options

memorySize (default 128)
name (default warmup-plugin-${service}-${stage})
schedule (default rate(5 minutes)) - More examples here.
timeout (default 10 seconds)

custom:
  warmup:
    memorySize: 256
    name: 'make-them-pop'
    schedule: 'cron(0/5 8-17 ? * MON-FRI *) // Run WarmUP every 5 minutes Mon-Fri between 8:00am and 5:55pm (UTC)'
    timeout: 20

Options should be tweaked depending on:

Number of lambdas to warm up
Day cold periods

Lambdas invoked by WarmUP will have event source serverless-plugin-warmup:

{
  "Event": {
    "source": "serverless-plugin-warmup"
  }
}

Cost

Lambda pricing here. CloudWatch pricing here. You can use AWS Lambda Pricing Calculator to check how much will cost you monthly.

Example

Free Tier not included + Default WarmUP options + 10 lambdas to warm, each with memorySize = 1024 and duration = 10:

WarmUP: runs 8640 times per month = $0.18
10 warm lambdas: each invoked 8640 times per month = $14.4
Total = $14.58

CloudWatch costs are not in this example because they are very low.

Contribute

Help us making this plugin better and future proof.

Clone the code
Install the dependencies with npm install
Create a feature branch git checkout -b new_feature
Lint with standard npm run lint

License

This software is released under the MIT license. See the license file for more details.

ikoif/serverless-plugin-warmup