Failure Friday


The aim of a regular Failure Friday is to prepare the SRE for all eventualities. It allows us to test our systems to the extreme finding any holes in resilience, monitoring and procedures.

Business communication#

  • Before every failure Friday, someone needs to be appointed as a business contact.
  • This person is to receive communication during the incident, relay back 'fake' business feedback, and then after it's over provide feedback on what went well and not well.


To perform a Failure Friday SRE need a set of scenarios to initiate to cause a failure. The following points provide guidance on what a scenario can be.

  • Don't be ridiculous (all 4 clusters are gone!)
  • Should be categorised under the following:
    • Security breaches
    • Human error
    • Service failures
    • Network issues
    • Data issues
  • Where to store scenarios?
    • Git repository for the SRE website
  • How to peer review?
    • Pull Requests on the SRE website Git repo
  • Anyone within the company can propose a scenario that SRE can perform


How do we prioritise what scenario we are going to do?

  • Base Failure Fridays on particular scenarios
    • Things that scare us the most
    • Things we've read about in recent articles or other company scenarios
    • Be experimental, think outside the box
  • Assign incident priority based on effects of the scenario
  • Build up a list of scenarios, pick randomly or specific based on worry


How do we monitor/alert on Failure Fridays?

  • A Scripted solution to add/remove monitors based from production to a test environment.

Resource selection#

  • Three roles
    • DM, (disaster master) implements the scenario
    • Primary, on call
    • Secondary, on call
  • Selection
    • Primary, whoever is on primary*
    • Secondary, whoever is on secondary*
    • DM, random selection from whoever left
  • *: if someone is missing out on FF by chance, this can be overridden
  • Primary responds to the incident, can page secondary if needed
  • These roles are selected from the pool of people eligible for on-call
  • People not eligible on-call can observe the response as 'flies on the wall'
  • DM is not allowed to divulge information about the scenario during the response


  • Failure friday starts on a Friday between 9 and 12, a specific time will be chosen by the DM and not communicated to anyone else
  • Failure friday can be veto'd last minute/canceled midway if there is an actual incident
  • No releases to prod (for SRE products) on Friday, unless critical/security patch

Failure Friday Setup#

  • DM keeps a timestamped log of every action taken to induce the failure
  • This log is added to the postmortem for further context, and so responders can calculate lead time on responses to different steps

Where to record results of failure Fridays?#

  • Postmortem produced as FF artifact, as if there was a real incident (standard procedures)
  • Additional sections:
    • Steps to induce the incident from DM
  • Everyone comes together to plan postmortem, no longer than 48 hours after incident (no later than Tuesday lunchtime)
  • Primary writes postmortem, peer-reviewed when complete before circulation
  • Completed postmortem is circulated to stakeholders, action items for improvement backlogged

Suggested Scenarios#

To Do#

  • Delete a set of nodes from a cluster. To simulate a node failing.


  • Delete a table in a database. To simulate corrupted or missing data.