40 questions / 10 random questions
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Which availability SLI best represents user experience for a search API?
Answer: The proportion of valid search requests that return contract-compliant results within the deadline
An availability SLI should measure the share of valid user requests that receive correct and timely responses, making it less dependent on internal topology.
For a 99.9% availability SLO over 30 days, approximately how much failure time is allowed?
Answer: About 43 minutes
Thirty days contain 43,200 minutes, and 0.1% is about 43.2 minutes. Production definitions must also state whether the SLI is time- or request-based, exclusions, and the window.
A short outage early in the month consumed 40% of a 30-day error budget. What is the appropriate response?
Answer: Evaluate burn rate and cause, reduce release risk, and prioritize reliability work
Burn rate shows whether continued consumption will violate the SLO. An error-budget policy should trigger proportionate release controls and reliability work.
Which alert design detects an SLO threat early while reducing pages from brief spikes?
Answer: Page when burn rate exceeds thresholds in both a short and a long window
Multi-window burn-rate alerting combines the responsiveness of a short window with confirmation from a longer window, paging on sustained budget threats.
Which condition is most appropriate for paging the on-call engineer?
Answer: User impact is ongoing, immediate human action is needed, and an actionable runbook exists
Pages should be reserved for urgent, actionable symptoms. Trends belong in tickets or forecasts, while informational events belong in dashboards or lower-urgency channels.
Database connection errors and API 5xx responses rise together. Which paging principle is best?
Answer: Page on the user-visible API success drop and link database metrics for diagnosis
A symptom-based page linked to causal dashboards reduces duplicate pages while connecting user impact to diagnosis.
What is the best basis for assigning alert severity?
Answer: Apply predefined criteria for user and business impact, urgency, and available workarounds
Shared severity criteria enable consistent staffing, notification scope, and update cadence. Internal error volume alone does not represent business impact.
Which HTTP request metric label is most likely to cause a cardinality explosion?
Answer: user_id
Metrics create a time series per label combination. Unbounded values such as user IDs or raw URLs should be avoided, with detailed lookup moved to logs or traces.
Which set of signals makes up the RED method for an online service?
Answer: Rate, errors, and duration
RED captures service demand and symptoms through request rate, errors, and duration. Resource saturation can be investigated with methods such as USE.
Which combination does the USE method examine for a node resource bottleneck?
Answer: Utilization, saturation, and errors
USE examines utilization, saturation or queuing, and errors for each resource such as CPU, memory, disk, and network.
Which metric type is appropriate for aggregating latency across instances and calculating a global p95?
Answer: A histogram with consistent buckets
Histogram bucket counts can be summed across instances and used to estimate a quantile. Averaging per-instance quantiles does not produce the global quantile.
Which mechanism links a latency spike in metrics directly to representative traces?
Answer: Attach exemplars containing trace IDs to histogram observations
Exemplars associate trace context with metric observations, allowing navigation from an anomalous bucket to a concrete request trace.
Tracing samples 10% in normal operation, but rare error traces should be retained. What is appropriate?
Answer: Use tail sampling in the collector to retain errors and high-latency traces preferentially
Tail sampling can decide after observing completed trace status and latency. Collector buffering, delay, capacity, and incident traffic still require design.
Which application log is both useful for incident diagnosis and appropriately limits sensitive data?
Answer: Record timestamp, level, service, event name, trace ID, and non-sensitive business identifiers as structured fields
Structured fields and correlation IDs support search, aggregation, and trace linkage. Secrets and unnecessary personal data should be masked or excluded.
How should asynchronous message processing be associated with the originating HTTP request trace?
Answer: Propagate producer context in the message and record a parent relationship or link on the consumer span
Propagating trace context or span links through message metadata preserves causality including queue delay. Incoming context should be validated across trust boundaries.
Logs from multiple hosts appear in an impossible order because clocks differ. What should be prioritized?
Answer: Monitor clock synchronization, distinguish event and ingest time, and supplement ordering with correlation IDs
Monitor synchronization such as NTP and retain both event and ingest timestamps. Use trace or message IDs to supplement causal ordering in distributed workflows.
What is most useful at the top of a service overview dashboard?
Answer: Key SLIs, SLO status, traffic, recent deployments, and links to dependency health
An overview should quickly show user impact and recent changes, then provide drill-down paths to diagnostic dashboards.
Internal metrics are healthy, but external users report login failures. Which monitoring addition is most useful?
Answer: Synthetic monitoring that periodically exercises the login flow from external locations
Synthetic monitoring continuously tests a critical journey through external DNS, CDN, TLS, and login paths, covering blind spots in internal monitoring.
Which telemetry measures regional page-rendering latency in real users' browsers?
Answer: Use RUM to aggregate navigation and web-vital data by bounded attributes such as region and version
Real user monitoring captures actual device, network, and delivery-path experience. Privacy, sampling, and attribute cardinality must be designed carefully.
During an incident telemetry volume surges and the collector queue fills. Which design is appropriate?
Answer: Monitor collector queue, drops, and export failures, with capacity limits and priority-aware sampling
The observability pipeline has capacity and failure modes. Define application backpressure, bounded buffering, priority retention, and visibility into dropped data.
During a major incident many engineers begin making changes at once and conditions worsen. What structure should be established first?
Answer: Name an incident commander and separate operations, communications, planning, and change authority
Explicit command and role separation prevent conflicting changes while technical work and communication proceed in parallel. The incident commander retains undelegated responsibility.
When should an incident receive an initial severity declaration?
Answer: Declare provisionally when impact and scope meet criteria, then revise as evidence changes
Severity is an initial decision used to activate response and communication. It should follow shared impact criteria without waiting for root-cause proof.
Which stakeholder update practice is appropriate during an incident?
Answer: Regularly share impact, start time, mitigation in progress, and the next update time
Separating facts from unknowns and committing to the next update reduces interruptions to responders and preserves trust.
Payment failures are expanding and the cause is still unknown. What is the first technical objective?
Answer: Contain impact with a safe rollback or traffic control while preserving evidence in parallel
During an incident, reducing user impact takes priority over proving root cause. Avoid irreversible actions and preserve timeline, logs, and change evidence.
Error rate rises immediately after a deployment. What preparation enables a fast rollback decision?
Answer: Define guardrail metrics, thresholds, observation windows, and automatic stop or rollback criteria before deployment
Predefined guardrails and version-aware telemetry distinguish normal variation from regression and speed canary stops or rollbacks.
An external recommendation service outage breaks the entire page. How should a feature flag be used?
Answer: Use a kill switch for recommendations and serve the core page in degraded mode
A feature-scoped kill switch isolates a noncritical dependency and preserves the core journey. Manage authorization, audit, defaults, and stale-flag cleanup.
What should an actionable runbook contain?
Answer: Triggers, impact checks, authorized diagnostics, safe mitigations, verification, escalation, and rollback
A runbook must be safe under pressure and state expected results and abort conditions for each step. Exercises should verify access and effectiveness.
The primary on-call has investigated for 15 minutes without reducing impact. What escalation is appropriate?
Answer: Escalate with context to the service owner or incident commander using predefined time and impact criteria
Escalation is a mechanism for adding time and expertise, not a failure. Pass impact, hypotheses, actions, outcomes, and the help needed.
Which practice creates an accurate incident timeline?
Answer: Record alerts, decisions, commands, changes, and observations with timestamps and actors in a shared log
A live incident document gives handoffs, parallel responders, and the postmortem a shared chronological record of facts and decisions.
How should incident command be handed to a responder in another region?
Answer: Review the live document verbally, obtain explicit acceptance, and announce the new commander to everyone
Explicit acceptance and announcement preserve one commander and one shared state. Handoff includes impact, changes, hypotheses, risks, and next actions.
Which statement should be avoided in a blameless postmortem?
Answer: Declare operator inattention as the sole root cause and end without system improvements
Stopping at individual blame leaves conditions that can trap another person. Examine design, tools, reviews, permissions, workload, and missing defenses.
Which postmortem action item is most actionable?
Answer: A specific prevention or detection improvement with owner, due date, completion criteria, and tracking ticket
Actions should be trackable and verifiable. Limit the list to high-value changes that reduce recurrence probability or impact.
A redundant system failed over successfully with no user impact. How should this near miss be handled?
Answer: Analyze the working defense, remaining margin, and conditions that could fail next time
A near miss reveals weaknesses without user harm. Verify that defenses behaved as designed and that capacity and recovery margins were sufficient.
Error rate has just returned to normal. What is needed before closing the incident?
Answer: Verify sustained key SLIs, cleared backlog, data consistency, removal of degradation, and recurrence monitoring
Recovery means more than errors stopping; delayed work, consistency, capacity, and temporary mitigations must all return to a stable state.
After database failover, the old primary may resume writes and create split brain. What control is required?
Answer: Fence the old primary and grant write authority only to the new primary using a generation or lease
Failover must exclude the old writer, not merely change routing. Fencing tokens, STONITH, or lease generations reject stale authority.
Backup jobs succeed every day. What additional check demonstrates recoverability?
Answer: Run regular restore drills in an isolated environment and verify integrity plus measured RTO and RPO
Backup success does not imply restore success. Test keys, access, procedures, dependencies, integrity, and elapsed recovery time through actual restoration.
CPU is normally 45%, and an event may double traffic. What is the appropriate capacity decision?
Answer: Load test service time, concurrency, and dependency limits, then reserve headroom including failure capacity
Validate headroom across database connections, queues, rate limits, scaling speed, and N+1 failure capacity. Load testing reveals nonlinear saturation.
An external address-validation API is down. Which degradation strategy safely continues order intake?
Answer: Perform minimal format checks, accept into a pending state, and revalidate after recovery
Where business rules allow, explicit deferred validation preserves the core flow. Design retries, deadlines, user communication, and deduplication.
Several deployments and configuration changes occurred just before an outage. What is the appropriate triage approach?
Answer: Overlay change events on the shared timeline and compare versions, affected scope, and control groups
A recent change is a strong hypothesis but timing alone does not prove causality. Compare version-aware telemetry and unchanged groups, recording each mitigation result.
What is the appropriate purpose and method for a game day in a production-like environment?
Answer: Define recovery hypotheses and success criteria, then inject bounded failures to test people, procedures, and telemetry
A game day is a hypothesis-driven exercise. Predefine blast radius, abort conditions, ownership, and rollback, then turn detection, communication, recovery, and verification gaps into actions.