Serverless Plugin Warmup

homepage icon https://github.com/FidelLimited/serverless-plugin-warmup

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Repo README Contents:

Serverless WarmUP Plugin ♨

serverless npm version npm downloads license

Keep your lambdas warm during Winter.

Requirements:

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
plugins:
  - serverless-plugin-warmup

You can enable WarmUp in general:

functions:
  hello:
    warmup: true

For a specific stage:

functions:
  hello:
    warmup: production

For several stages:

functions:
  hello:
    warmup:
      - production
      - staging
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}-*

If using pre-warm, the deployment user also needs a similar policy so it can run the WarmUp lambda.

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
}

Options

custom:
  warmup:
    cleanFolder: false,
    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
    prewarm: true // Run WarmUp immediately after a deployment
    folderName: '_warmup' // Name of the folder created for the generated warmup lambda

Options should be tweaked depending on:

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

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

Artifact

If you are doing your own package artifact set option cleanFolder to false and run serverless package. This will allow you to extract the warmup NodeJS lambda file from the _warmup folder and add it in your custom artifact logic.

Gotchas

If you are deploying to a VPC, you need to use private subnets with a Network Address Translation (NAT) gateway (http://docs.aws.amazon.com/lambda/latest/dg/vpc.html). WarmUp requires this so it can call the other lambdas but this is applicable to any lambda that needs access to the public internet or to any other AWS service.

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:

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

Contribute

Help us making this plugin better and future proof.

License

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