One of the most powerfull services from AWS is Autoscaling. AWS Autoscaling allow scale EC2 instances up and down automatically. Another powerfull tool is Chef or other tool to automating infrastructures. The combination off both is a great solution to manage your applications in the cloud.

To integrate AWS Autoscaling with Chef, is necessary communicate to Chef Server when an instance is up or down. When new instance boot, chef-client register new instances to Chef Server, but when a instance shutdown anyone communicate with the Chef Server. To do it, I use AWS SQS, where AWS Autoscaling](https://aws.amazon.com/autoscaling/) publish a message when instance down. And in the Chef Server, I use an script to get the messages and delete node in Chef Server.

AWS Autoscaling and chef server integration

Next, there are the details to configure AWS Autoscaling to work with Chef Server

Generate custom AMI

The proposes of generate a custom AMI are:

  • Install chef-client and pre-configure it.
  • Reduce the boot time when AusoScaling up an new instance.

I use cloud-init to customize new instances in boot time. The next script is the basic bootstrap.txt that add node name to chef-client configuration and run the chef-client.

#!/bin/bash
set -x -e

_node_name="node-`ec2metadata --instance-id`"
echo "node_name '$_node_name'" >> /etc/chef/client.rb
echo '{"run_list":["role[base]","role[webserver]"]}"' > /etc/chef/first-boot.json
chef-client -N "$_node_name" -E "production" -L "/var/log/chef-client-first-boot-log" -j /etc/chef/first-boot.json

Configure AWS queue to notify that an instances terminate.

Create IAM user with SQS access and copy user ARN (arn:aws:iam:::user/devops)

Create a SNS topic AutoScalingDown

ARN: arn:aws:sns:eu-west-1::AutoScalingDown

Create SQS queue DeregisterChefServer and allow user ARN to receive message action.

  • ARN: arn:aws:sqs:eu-west-1::DeregisterChefServer

  • URL: https://sqs.eu-west-1.amazonaws.com//DeregisterChefServer

Add permitions to SQS queue DeregisterChefServer

IAM User:

  • Effect: Allow

  • Principal: arn:aws:iam:::user/devops

  • Action: receiveMessage

SNS ARN:

  • Effect: allow

  • Principal: everybody

  • Action: All

  • Conditions:

    • Condition: ArnEquals
    • Key: aws:SourceArn
    • Value: arn:aws:sns:eu-west-1::AutoScalingDown

Create a SNS subcription:

  • Topic ARN: arn:aws:sns:eu-west-1::Superpop2AutoScalingDown

  • Protocol: Amazon SQS

  • Endpoint: arn:aws:sqs:eu-west-1::DeregisterChefServer

Create a notification in AutoScaling Group:

Send a notification to: AutoScalingDown (arn:aws:sqs:eu-west-1::DeregisterChefServer) Whenever instance: terminate

Script to subcribe to AWS queue and remove nodes from Chef Server

To get message from AWS SQS and delete nodes in Chef Server, I have developed a small php script to run from cron. It use aws-sdk-php api to connect to AWS SQS and get messages from AWS Autoscaling and run knife to delete node and client from Chef Server.

Install the next script in /usr/local/awssgs2chefserver directory:

<?php

require '/usr/local/awssgs2chefserver/vendor/autoload.php';

use Aws\Sqs\SqsClient;

$queueUrl = 'https://sqs.eu-west-1.amazonaws.com/<aws account number>/DeregisterChefServer';

$client = SqsClient::factory(array(
    'profile' => 'my_aws_profile',
    'region'  => 'eu-west-1'
));

try {

  $result = $client->receiveMessage(array(
    'QueueUrl' => $queueUrl
  ));

  if ($result['Messages'] == null) {
    exit;
  }

  $result_message = array_pop($result['Messages']);
  $queueHandle = $result_message['ReceiptHandle'];
  $messageBody = $result_message['Body'];

  $body = json_decode($messageBody, true);
  $message = json_decode($body['Message'], true);
  $delete_node = "/usr/bin/knife node delete node-" . $message['EC2InstanceId'] . " -y";
  $delete_client = "/usr/bin/knife client delete node-" . $message['EC2InstanceId'] . " -y";

  $result = system($delete_node);
  if (!$result) {
    echo "failed to delete node node-" . $message['EC2InstanceId'] . "\n";
  }

  $result = system($delete_client);
  if (!$result) {
    echo "failed to delete client node-" . $message['EC2InstanceId'] . "\n";
  }

  $client->deleteMessage(array(
    'QueueUrl' => $queueUrl,
    'ReceiptHandle' => $queueHandle
  ));

} catch (Exception $e) {
    die('Error receiving message to queue ' . $e->getMessage());
}
?>

Create a composer.json file /usr/local/awssgs2chefserver/composer.json to install aws-sdk-php:

{
    "require": {
        "aws/aws-sdk-php": "2.*"
    }
}

Install and run composer:

curl -sS https://getcomposer.org/installer | php
php composer.phar install

Create /usr/local/awssgs2chefserver/.chef directory and add:

  • admin.pem

  • trusted_certs/.crt

  • knife.rb

# See https://docs.getchef.com/config_rb_knife.html for more information on knife configuration options

current_dir = File.dirname(__FILE__)
log_level                :info
log_location             STDOUT
node_name                "admin"
client_key               "#{current_dir}/admin.pem"
validation_client_name   "<organization>-validator"
validation_key           "#{current_dir}/<organization>-validator.pem"
chef_server_url          "<chef server url>"
cookbook_path            ["#{current_dir}/../cookbooks"]

Create a AWS credentials for IAM user in /root/.aws/credentials

[my_aws_profile]
aws_access_key_id = <IAM access key>
aws_secret_access_key = <IAM secret key>

Install chefdk.

Run script from cron creating the /etc/cron.d/awssgs2chefserver file:

* * * * *   root    cd /usr/local/awssgs2chefserver; /usr/bin/php /usr/local/awssgs2chefserver/awssgs2chefserver