Learn vocabulary for designing, proposing, and discussing Service Level Indicators.
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What is an SLI (Service Level Indicator)?
An SLI is a specific, quantitative measure of service behaviour. Examples: request success rate, latency (99th percentile), availability, error rate.
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Which is a well-formed SLI definition?
A well-formed SLI is specific: it names the metric (latency), the percentile (p99), the measurement window (1 minute rolling), and any exclusions (health checks).
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What does 'coverage' refer to when designing SLIs?
SLI coverage refers to how much of a service's user-visible behaviour is measured by SLIs. Good SLI coverage means you can detect most user-impacting issues.
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What does 'SLI proposal language' include?
An SLI proposal should include: the metric definition, how it is measured, why this metric represents user happiness, the proposed target, and known limitations or exceptions.
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What is the difference between an SLI and an SLO?
The SLI is the measurement (e.g., 'success rate'). The SLO is the objective — the target value the SLI must meet (e.g., 'success rate ≥ 99.9% over 30 days').
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Review Comment: 'The response time for the /users endpoint is consistently above 200ms. Consider adding a dependency on Redis to cache frequently accessed user data. This should improve performance.' What does the reviewer *primarily* suggest?
This comment focuses on performance optimization. The reviewer isn't asking for general testing or infrastructure changes; they're specifically pointing to a potential bottleneck – slow response times – and suggesting a targeted solution: caching using Redis. The incorrect options address broader system design considerations that aren't directly related to the immediate problem described.
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Slack Message: '@john.doe, just ran the SLI dashboard and saw a huge spike in error_rate for the payment service! Looks like it jumped from 1% to 15%. Need to investigate ASAP.' What is John *most* concerned about?
John's message highlights an active SLI failure. The phrase 'SLI dashboard' and the specific mention of 'error_rate' immediately indicate that a key metric is not meeting its target. While other options are plausible causes, they aren't directly linked to the reported SLI breach in this communication – focusing on code deployments or data quality would require more context.
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PR Description: 'Implemented a new caching layer for the /products API endpoint to improve response times. The SLI for 'API Response Time' was updated to include this cache hit rate.' What is the *primary* purpose of updating the SLI in this PR?
The update to the SLI is directly tied to measuring the impact of the change. Updating an SLI's definition (including metrics like cache hit rate) is crucial for ensuring that monitoring tools continue to accurately reflect performance after a system modification. The other options are secondary concerns or potential outcomes, not the core reason for the update.
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Standup Update: 'I've been working on improving the SLI coverage for our user authentication service. We're now tracking both successful login attempts and failed login attempts as separate indicators.' What does 'SLI coverage' refer to in this context?
'SLI coverage' describes the scope of monitoring. It means that multiple SLIs are being used to provide a holistic view of the authentication service's health – not just one metric (e.g., successful logins). This indicates a more comprehensive approach to measuring and tracking service performance.
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Code Review Comment: 'The SLI for 'Request Latency' doesn't include any measurements during peak hours. This is a significant omission – we need to understand how the service performs under load.' What does this comment suggest should be added to the SLI definition?
The reviewer is advocating for realistic monitoring. Simply defining a 'Request Latency' SLI without considering peak load is insufficient because it won't reveal how the service actually performs under real-world conditions. Including measurements during periods of high traffic is essential for a meaningful and actionable SLI definition.
What will I practise in "SLI Design — Vocabulary and Discussion Language"?
This module focuses on Observability Engineering — real workplace phrasing you'll use on the job. It contains 10 scenario-based multiple-choice questions with instant feedback.
Is this exercise free to use?
Yes. Every exercise on CoderSlingo, including this one, is free to use with no account or sign-up required.
How many questions does this exercise have?
This module includes 10 questions. Each one gives an immediate right/wrong result plus a full explanation of the correct phrasing.
What happens if I answer a question incorrectly?
You'll see the correct answer highlighted straight away, along with a plain-English explanation of why it's right and why the other options don't fit — mistakes are part of the learning here.
Can I retry the exercise if I want a better score?
Yes — use the 'Try again' button on the results screen to reset your score and go through the questions again. There's no limit on attempts.
Who is this Observability Engineering exercise for?
It's aimed at IT professionals with working English who want to sound more natural and precise around observability engineering — useful whether you're preparing for real conversations at work or just building confidence with the vocabulary.
Do I need an account to track my progress?
No account is needed. Your progress through the exercise is tracked locally in your browser for the current session, and you can replay the module at any time.
How is this different from reading a blog article?
This exercise is an interactive drill that tests and reinforces specific phrasing through multiple-choice questions with instant feedback, while blog articles explain concepts and vocabulary in prose. The two work well together.
Where can I find more Observability Engineering exercises?
See the Observability Engineering hub for more modules like this one, or browse the full Exercises page for other IT-English topics.
Can I complete this exercise on my phone?
Yes — every exercise on CoderSlingo is fully responsive and works on phones and tablets, so you can practise anywhere.