Reliability
On this page 8 topics
Overview
Topics
- SLIs
- SLOs
- error budgets
- availability
- latency percentiles
Learn first
2 h of practice (estimate)
Learning outcomes
- Define SLIs that reflect user experience (availability, latency percentiles, correctness).
- Set SLOs and compute error budgets.
- Alert on error-budget burn rate.
- Explain how error budgets guide release and reliability decisions.
Lessons
Lab and exercises
Lab
MID-049-LAB1 · Checkout SLOs
Outcomes: 1–4 · Time: ~2 h Define SLIs and SLOs for checkout and search, with burn-rate alerts, and write a short SLO document including the budget policy. Acceptance: SLO document reviewed; alerts tested with injected errors.
Exercises (assessment: SLO document review)
| ID | Outcome | Task |
|---|---|---|
| MID-049-EX01 | 1 | For Shop's search and checkout, write one availability SLI and one latency SLI as good/valid ratios. |
| MID-049-EX02 | 1 | Explain why a SLI measured inside the service can miss failures users see. |
| MID-049-EX03 | 2 | Compute the error budget in requests and in minutes for a 99.9% SLO over 30 days with 10 million requests. |
| MID-049-EX04 | 2 | Propose an SLO for search and justify why it is not 100%. |
| MID-049-EX05 | 3 | Write a two-window burn-rate alert (page and ticket) for checkout. |
| MID-049-EX06 | 4 | Write a budget policy with actions at three remaining-budget levels. |
| MID-049-EX07 | 1–4 | Review a sample SLO document with a 100% target and server-side SLIs; list fixes. |
Show solutions
- EX01 Availability: successful checkouts / valid checkout requests; latency: search responses under 300 ms / all search responses.
- EX02 Requests rejected at the load balancer or gateway, or timeouts before reaching the service, never appear in service metrics.
- EX03 Budget 0.1%: 10,000 failed requests; about 43.2 minutes of full outage (30 days × 24 h × 60 × 0.001).
- EX04 For example 99.5% of searches under 300 ms; users tolerate an occasional slow search; the cost of 100% is unbounded.
- EX05 Page: 1h and 5m ratios above 14 × 0.001; ticket: 6h and 30m above 6 × 0.001 (thresholds are a team choice).
- EX06 Above 50%: normal releases; 10-50%: extra review and canaries; below 10%: reliability work only until recovered.
- EX07 Replace 100% with a realistic target, measure at the gateway, add the budget policy and burn-rate alerts.
Quiz
Outcomes: O1 SLIs · O2 SLOs and error budgets · O3 burn-rate alerts · O4 using the budget.
A self-check for you: nothing is graded, saved or sent anywhere. Choose an answer, then check it. You can try again as often as you like.
Practical part
Seven exercises MID-049-EX01 to EX07 (EX07 is the SLO document review) plus the checkout SLO lab. Pass: at least five exercises and a lab with a reviewed SLO document and burn-rate alerts tested by injected errors.
Common mistakes
100% targets; SLIs measured at the server rather than as users experience them.
Assessment
SLO document review.
Career relevance
SLO engineering (SRC-012).