Gunslinger

A cloud resiliency tool, inspired by Chaos Monkey and written in Node.js for AWS Lambda.

Caveat Emptor: This is still alpha software, and some actions may incur additional AWS charges.

Usage

$ npm install --save gunslinger

Function code:

exports.run = require('gunslinger')(require('./config'));

Configuration:

{
  "armed": false,
  "store": ["simple_db", "GunslingerEvents"],
  "notifier": ["sns", "arn:aws:sns:eu-west-1:123456789012:Gunslinger"],
  "grouper": "asg",
  "filters": [
    ["tag", "gunslinger"],
    ["redundancy", 2],
    ["probability", 0.15],
    ["action_limit", 1]
  ],
  "actions": [
    "burn_cpu",
    "fill_disk",
    "terminate"
  ],
  "ssh": {
    "user": "ec2-user",
    "privateKey": "/path/to/key.pem",
    "publicIp": true
  }
}

Create SimpleDB and SNS resources:

$ aws configure set preview.sdb true
$ aws sdb create-domain --domain-name GunslingerEvents
$ aws sns create-topic --name Gunslinger

Create a function:

$ aws lambda create-function --function-name Gunslinger --zip-file fileb:///path/to/code.zip --role GunslingerExecution --handler index.run --runtime nodejs4.3

The GunslingerExection role should have sns:Publish, sdb:PutAttributes, sdb:Select, autoscaling:DescribeAutoScalingGroups, ec2:DescribeInstances and ec2:TerminateInstances permissions.

Create a schedule and apply it to your function:

$ aws events put-rule --schedule-expression 'cron(0 9-16 ? * MON-FRI *)' --name GunslingerPerHourOfficeHours
$ aws lambda add-permission --function-name Gunslinger --statement-id 1 --action lambda:InvokeFunction --principal events.amazonaws.com --source-arn arn:aws:events:us-east-1:123456789012:rule/GunslingerPerHourOfficeHours
$ aws events put-targets --rule GunslingerPerHourOfficeHours --targets '{"Id" : "1", "Arn": "arn:aws:lambda:us-east-1:123456789012:function:Gunslinger"}'

Pro Tip: If you need to generate more sophisticated schedules, check out crongen.

Configuration

armed (default = false)

The default mode of Gunslinger is "unarmed". In this mode, no destructive action is taken. Before you switch to the "armed" mode, verify your filter configuration. Without any filters, Gunslinger will target every auto scaling group within your AWS account on each invocation!

store (required)

Gunslinger will persist events (such as instance termination) to maintain a record for future invocations. Currently, only SimpleDB is supported.

notifier (default = none)

Optionally, Gunslinger can push events to a notification service. Currently, only SNS is supported.

grouper (default = asg)

Gunslinger targets logical groups of EC2 instances. Currently, only auto scaling groups are supported.

filters (default = [])

The set of target groups can be reduced by applying one or more of the following filters:

• action_limit(N): allow at most N actions on any given group within a 24-hour window.
• probability(N): only take action on any given group with a probability of 0 <= N <= 1.0.
• redundancy(N): only take action on groups with N or more healthy instances.
• tag(K): only take action on groups tagged with key K.

actions (default = [])

When a group is targeted, a target action is randomly selected out of this configured set. Please consult the source for available actions.

VPC usage

Unless publicIp is explicitly set to true, Gunslinger will attempt to SSH to the private IP addresses of instances. To use this mode, you must add a VPC configuration to your Lambda function.