Serverless Plugin for Application Load Balancer

This plugin compiles ALB events to Lambda Target Groups and ALB Listener Rules (as CloudFormation resources). It does not create a new ALB, it requires an existing ALB with a HTTP or HTTPS listener.

Requirements

• Node.js >= v8.10
• Serverless Framework >= v1.40

Installation

Using yarn:

yarn add --dev serverless-plugin-alb

Add the plugin to your serverless.yml file:

plugins:
  - serverless-plugin-alb

Usage

serverless deploy

Configuration

You can specify a custom config file in your serverless.yml:

custom:
  alb:
    listenerArn: <listenerArn> (required)
    host: <yourdomain.com> (optionnal)

You can add one or more alb event for each functions:

# serverless.yaml
functions:
    hello:
        handler: handler.hello
        events:
          - alb:
              priority: 1
              conditions:
                path: '/hello'
          - alb:
              priority: 2
              conditions:
                host: somehost.com
                path: '/greetings'

For each alb event, property priority and at least one of conditions are required.

Here are the supported conditions:

• path (String)
• host (String or Array)
• method (String or Array)
• query (Object) A list of key/value
• header (Object) Must have name and values properties
• ip (String or Array) Must be a CIDR block

Note: there can be up to 5 conditions in total. If you specify multiple values for a field name (such as query or `host), it counts as multiple conditions.

How it works

For each functions with at least one ALB event, the plugin will create a target group for that function and an InvokeFunction permission allowing ALB service to invoke that function.

Then for each ALB event, a listener rule will be created onto the provided listener with the conditions defined in the ALB event (path-pattern or/and host) and a "Forward to" action to the function target group.

Limitations

Update rule priorities is tricky. For example, take the previous serverless.yml definition and swap the priorities like this:

# serverless.yaml
functions:
    hello:
        handler: handler.hello
        events:
          - alb:
              priority: 2
              conditions:
                path: '/hello'
          - alb:
              priority: 1
              conditions:
                host: somehost.com
                path: '/greetings'

Then the Cloudformation stack update will fail saying that a priority is already in use: CloudFormation does not handle rule re-ordering. You have to use different priorites each time you add or delete functions.