Server Scared of Downtime

Servers are scared of downtime!

The following Ansible playbook provides a simple but powerful way to compare instance uptime to a threshold “scale_time” variable that you can set in your pipeline variables in Github. By checking the uptime, you can selectively run tasks only on machines newer than that time period you set to avoid downtime on the rest.

Of course the purpose of Ansible is to be idempotent but sometimes during testing we might need to isolate servers to not affect all, specially when using dynamic inventories.

Solution: The Playbook

Ansible Playbook to target new only in scale set
Playbook Link

How it works:

  1. Create a variable in Github Pipeline Variables.
  2. Set the variable at runtime:
ansible-playbook -i target_only_new_vmss.yml pm2status.yml -e "scaletime=${{ vars.SCALETIME }}"
  • The set_fact task defines the scale_time variable based on when the last scaling event occurred. This will be a timestamp.
  • The uptime command gets the current uptime of the instance. This is registered as a variable.
  • Using a conditional when statement, we only run certain tasks if the uptime is less than the scale_time threshold.
  • This allows you to selectively target new instances created after the last scale-up event.

Benefits:

  • Avoid unnecessary work on stable instances that don’t need updates.
  • Focus load and jobs on new machines only
  • Safer rollouts in large auto-scaled environments by targeting smaller batches.
  • Easy way to check uptime against a set point in time.