1. Cycling Instances Or, don’t hurt me, I’m ephemeral!

3.  Getting security updates on Ubuntu AMI’s  The auto-scaling group is in control!  Rebooting will spook the scaling group The Problem

4.  AWS Linux AMI  Get updates at first boot with cloud-config  Based on RHEL  CoreOS  Nice FastPatch updating scheme  It’s different The Solution(s)

6.  Use cloud-init to update ubuntu ami on first boot  Use unattended upgrades to keep mostly up to date Pros  Standard approach  Easy to implement Cons  Pfaff  Basic implementation, intelligence requires more change The Minimal Solution

7.  Autoscale up, getting the new ubuntu AMI with security updates and salt installing new stuff too  Once Autoscaling is complete, check that new EC2 instance is ‘good’ by checking the ELB health check  Terminate old instance to return to desired instance count Cycling Instances – The Plan

8.  ASG sets new instance to Inservice/Healthy when EC2 checks pass  Only calls the ELB healthcheck after the HealthCheckGracePeriod  So we only know we’ve been successful after…  Start instance  EC2 Healthcheck Passed  HealthCheckGracePeriod  ELB healthcheck passed  Actually up! Cycling Instances – The Problem(s)

10. The ASG Lifecycle

11.  Scale out the ASG by one  New instance goes from pending -> in service and healthy  ASG has new instance as in-service and healthy  EC2 Healthcheck has been passed  ELB has instance out-of-service as no health check passed

12.  Waiting for grace period before checking ELB health check  ASG checks ELB health check for the first time  Health check fails, EC2 instance is terminated

13.  Create new instance as before  New instance has not passed health check yet  New instance in healthy and on-service in ASG

14.  This time, ELB health check has passed  There are 2 healthy instances in the ELB

15.  The new instance was created successfully  The old instance has been terminated

16.  Standard way of getting security updates  Enforces cloudy design principles  Can be automated Cloudy By Design

18.  More intelligent scaling, scale-out, scale-in, with specific policy  Auto-scaling group has Scheduled Actions, we can cycle instances by default on a cron-like schedule  Switch to a more cloud friendly AMI? The Future

20. The End