rallytime / ec2-autoscale-reactor

Autonomous Minion Management via EC2 Autoscaler

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This is a reactor formula, which allows the autoscaling feature in EC2 to notify Salt when an instance is created, so that it may be automatically bootstrapped and accepted by the Salt Master, or when an instance is deleted, so that its key can be automatically removed from the Salt Master.


The following packages must be installed:

- Salt (develop branch)

Master Configuration

The following files need to be configured on the Salt Master:

- /etc/salt/master
- /etc/salt/cloud.providers.d/ec2.conf
- /srv/reactor/ec2-autoscale.sls (from this package)


This reactor makes use of the web hooks system introduced in Salt API 0.8.4. The configuration for Salt API is stored in the master configuration file:

      - .*
      - '@runner'
      - '@wheel'

  port: 8080
  webhook_url: /hook
  webhook_disable_auth: True

When a web request is received, Salt API will fire an event for the reactor system to pick up:

  - 'salt/netapi/hook/ec2/autoscale':
    - '/srv/reactor/ec2-autoscale.sls'

This reactor will examine the web hook received from EC2 and check its authenticity. If issues are encountered, such as an invalid signature, or the certificates being located outside of Amazon, a notification will be sent to the user via email. The following settings are an example of SMTP settings that might be used to connect to the mail server:

smtp.from: 'salt-master@example.com'
smtp.to: admin1@example.com.com; admin2@example.com.com
smtp.host: smtp.gmail.com
smtp.username: 'salt-master@example.com'
smtp.password: 'verybadpass'
smtp.tls: True
smtp.subject: 'Salt'

Finally, some extra settings must be set up to point the reactor to the necessary Salt Cloud provider setting. Any additional settings to be used on the target minion, that are not configured in the provider configuration, can also be set here.

  provider: my-ec2-config
  ssh_username: ec2-user


Existing Salt Cloud provider configuration can be used with this reactor. Profile configuration is not necessary on the master; minions will be configured as per the EC2 Autoscaling Group.

  id: <aws id>
  key: <aws key>
  keyname: <my key name>
  securitygroup: <my security group>
  private_key: </path/to/my/priv_key.pem>
  location: us-east-1
  provider: ec2
    master: saltmaster.example.com


This package includes a file in its reactor/ directory called ec2-autoscale.sls. Create the /src/reactor/ directory on the Salt Master if it doesn't already exist, and copy this file into it.

EC2 Configuration

The following must be configured in the EC2 account to be used:

- SNS HTTP Notification
- Launch Configuration
- Autoscaling Group

SNS HTTP(S) Notification

In order to notify the reactor that an instance is being autoscaled up or down, AWS SNS must be configured with the URL to send the notification webhook to. Both HTTP and HTTPS are available, but it is highly recommended that HTTPS is used.

From the AWS Console, select SNS (Push Notification Service). This will take you to the SNS dashboard.

Click the button to Create New Topic. Enter a Topic Name, and a human-readable Display Name, and select the Create Topic button. This will take you to the Topic Details area.

Inside the Topic Details, click the button to Create Subscription. Select HTTP or HTTPS as appropriate, and enter the URL to your Salt API server as the endpoint. Assuming it is set up at https://saltmaster.example.com/, the endpoint will look like:


In this URL, /hook notifies Salt API that a webhook is being used, and /ec2/autoscale will be used to tag the event that the reactor uses to process it. The tag that will be created by this URL will be


Clicking the Subscribe button will cause a subscription notification to be sent immediately to the endpoint. If the Master configuration is correct, the reactor will forward the subscription notication to the configured email address(es). This message will contain a subscribe URL which, when visited, will activate the Subscription.

If the Salt Master is not properly configured, the endpoint can be re-entered, and another subscription notifcation will be sent. It should be noted that once configured, a subscription may not be deleted via the web interface until the subscribe URL has been visited and confirmed.

Launch Configuration

In order to start autoscaling instances, EC2 requires a launch configuration to be set. This defines the EC2-specific variables (AMI, disks, etc.) that will be used to spin up new instances.

From the AWS Console, select EC2 (Virtual Servers in the Cloud), which will lead to the EC2 Management Console. From there, select Launch Configurations from the left-hand menu.

Click the Create Launch Configuration button. Follow the wizard to select the appropriate AMI and configuration to use. At the Review screen, click the Create Launch Configuration button to save.

Autoscaling Group

Once a launch configuration is defined, an autoscaling group may be configured which defines variables such as the minimum and maximum number of instances, and under what circumstances to add and remove instances.

From the AWS Console, select Auto Scaling Groups from the left-hand menu. Click the Create Auto Scaling Group button. Select the option to "Create an Auto Scaling group from an existing launch configuration". Select the Launch Configuration, and click Next Step.

Follow the wizard to the "Configure Notifications" screen. Click the "Add Notification" button and select the notification that was configured on SNS. Complete the wizard as normal.

Basic Usage

Once the Salt Master and AWS have been configured, the reactor will manage itself. When the autoscaler adds a new instance, Salt Cloud will be notified to wait for it to become available, and bootstrap it with Salt. Its key will be automatically accepted, and if the minion configuration includes the appropriate startup state, then the minion will configure itself, and go to work.

When the autoscaler spins down a machine, the Wheel system inside of Salt will be notified to delete its key from the master. This causes instances to be completely autonomous, both in setup and tear-down.


As instances will be launched and destroyed automatically by EC2, they will not have the opportunity to be configured with user-definable names, and will therefore be identified to the master by their instance-id. In the event that more detailed identifying information needs to be available, the instances should be configured to include EC2 tags, which can later be read and displayed to the user via Salt Cloud.

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Autonomous Minion Management via EC2 Autoscaler



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