Intro to Lambda using Ansible

Here's a simple example of an AWS Lambda using Ansible to set it up.

Lambda is another example of AWS's crazy none-intuitive naming convention. I highly recommend you bookmark AWS in Plain English, an excellent site that demystifies AWS's whimsical names. Name aside, Lambda is serverless way to run your code.

Serverless sounds like witchery but, like all cloud, it's simply someone else's server. One of the key concepts of AWS is that its services are often built on top of other services. An RDS instance is, behind the scenes, built on top of an EC2 instance. If you really want to understand AWS, learn the foundation: VPC, EC2, IAM, and ELB.

Lambda is no exception, it's a service for running your code on short lived pre-built containers. The containers are pre-built and you load your supported (Node.js, Java, C#, Python, and Go at this time) code onto them to run. Let's look at a super simple example and deploy it using Ansible.

The code

This code returns a data structure and nothing else.

    def my_lambda(event, context):
        '''The name of this sub must match the lambda handler, and the two 
        parameters are required.'''
        
        # Return whatever you like.
        return [ 
                 { "context_function_name": context.function_name },
                 { "event": event },
                 { "test": "one", "result": "pass" },
                 { "test": "two", "result": "pass" }
               ]

Any parameters you pass go into the 'event' parameter. What is returned will end up in stdout. Context is a object that contains information about the instance of the lambda.

The playbook

Zip the Lambda

The Lambda, be it one file or many, must be in a zip file.

---
- hosts: localhost

  tasks:
    - name: archive lambda
      archive:
        path: ./lambda.py
        format: zip

Upload the Lambda

Make the Lambda. Note the handler, it's the name of the Lambda and the function in the code that will be called. Every Lambda needs an IAM role, here I make it a variable that I can define elsewhere.

- name: my lambda function
  lambda:
    state: present
    name: my_lambda
    zip_file: lambda.py.zip
    runtime: python2.7
    handler: lambda.my_lambda
    role: "{{ role }}"
    tags:
      'responsible party': nwatson@example.com

Run the Lambda

This executes the Lambda passing the payload as arguments. They go into the 'events' parameter.Wait waits for the Lambda to finish. Finally we save the results with register.

- name: Run my lambda
  execute_lambda:
    name: my_lambda
    payload:
      arg1: foo
      arg2: bar
    wait: true
  register: my_lambda

Remove the Lambda

- name: my lambda function
  lambda:
    state: absent
    name: my_lambda

The results

- debug:
    msg: "{{ my_lambda }}"

Here they are:

PLAY [localhost] ********************************************************

TASK [Gathering Facts] **************************************************
ok: [localhost]

TASK [archive lambda] ***************************************************
changed: [localhost]

TASK [my lambda function] ***********************************************
changed: [localhost]

TASK [Run my lambda] ****************************************************
changed: [localhost]

TASK [my lambda function] ***********************************************
changed: [localhost]

TASK [debug] ************************************************************
ok: [localhost] => 
  msg:
    changed: true
    failed: false
    result:
      logs: ''
      output:
      - context_function_name: my_lambda
      - event:
          arg1: foo
          arg2: bar
      - result: pass
        test: one
      - result: pass
        test: two
      status: 200

PLAY RECAP **************************************************************
localhost                : ok=6    changed=4    unreachable=0    failed=0   

There's a lot more to Lambdas; I encourage you to read up on them. Also know that Lambda is not unique. Other container technologies like Kubernetes and Cloud Foundry can run short duration containers. You can find the the code for this post here.