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Reliability

How many nines you need, and what each one costs.

availabilitySLASLOSLIfault toleranceredundancyfailoverbackupsdisaster recoverymulti-region

Lessons

  1. 15.1SLIs, SLOs, SLAs and error budgetsThree confusing acronyms, one simple idea: measure what users feel, set a goal, and promise a bit less than you deliver. 30 min The nines
  2. 15.2The nines: how much availability do you need?99.9% sounds almost perfect. Turn it into minutes of downtime and you'll see why each extra 9 changes everything. 30 min The nines The nines
  3. 15.3Redundancy and failoverMachines break all the time. Here's how to keep the service running when one does, without making things worse. 30 min The nines CAP: partition the network
  4. 15.4Disaster recovery: backups, RPO/RTO and multi-region strategiesSpares save you from a dead server. Disaster recovery saves you from a lost region, deleted data, or an attacker. 30 min The nines

On the job: try it on your own project

With your team, pick the one user journey that matters most. Ask Claude Code to propose an SLI for it, compute the current value from logs or monitoring, and suggest a realistic SLO. Then check when backups last ran and whether a restore was ever tested. Write a one-page reliability sheet: SLO, error budget, backup status and one gap.

Can you do this now?

0/4. Anything you can't tick yet: reopen that lesson's practice ladder.