Serverless Plugin for Application Load Balancer

Warning: Since Serverless v1.46 was released, ALB events are supported natively so you do not need this plugin unless you are using an earlier version of Serverleess.

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

Tested with:

• 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.