Interview questions in DevOps & Cloud, page 5
What is an error budget?
Error budget is one minus the SLO, the allowed unreliability; it gates feature velocity versus reliability work.
How Compose services reach each other by name
Services share a default network and the web app uses the database's service name as the hostname; Docker's embedded DNS resolves it to the container IP.
Protecting object storage from accidental loss
Enable versioning, MFA delete or object lock, cross-region replication, and least-privilege policies.
How would you design a multi-arch build process and anticipate challenges?
Mention buildx or cross-compilation, split native and emulated builds, cache per-arch layers.
Proposing availability and latency SLIs for an auth API
Availability as the ratio of successful valid requests; latency as the fraction served under a threshold; measure at the edge from the user's view.
Docker Compose default networking
Compose creates one default user-defined bridge network for the project; all services join it and reach each other by service name via embedded DNS, isolated from other projects.
Object storage tiers and lifecycle automation
Tiers trade storage price for retrieval cost and latency; automate with lifecycle rules or intelligent tiering.
How would you integrate artifact signing into CI/CD and secure the keys?
Tests supply chain architecture and secrets management. A strong answer: remote HSM or KMS signing isolated from build runners, signature verification at deploy gates, and key rotation with audit logging.
Diagnosing a healthy p50 but breaching p99
One percent of requests are slow, hurting power users and fan-out calls; investigate GC, locks, contention, cold caches, retries.
Manage startup order and readiness in Compose
Depends_on only orders start, not readiness; add a healthcheck to the DB and use depends_on with condition: service_healthy so the web app waits until the DB passes its health check.
Maximizing object-store throughput for small files
Spread keys across prefixes for partition parallelism, batch small files, parallelize and use multipart uploads.
What is a CI/CD quality gate? Give a simple example.
Thresholds blocking merges; a minimal new-code gate with 0 critical issues & 70% new-code coverage.
Defining SLOs for a new critical service
Start from user journeys, pick SLIs, involve product, engineering, and business stakeholders, set realistic targets iteratively.
Compose image directive versus build directive
Image pulls a prebuilt image from a registry; build builds from a local Dockerfile and context; use build for your own custom application code.
Object store vs NFS consistency models
S3 gives strong read-after-write per object with no partial updates; NFS offers close-to-open with shared mutable files.
Difference between unit and integration tests and CI pipeline placement
Unit tests isolate code and run fast in the build stage; integration tests verify real wiring later. Target 70 percent unit tests.
Handling planned maintenance in SLOs and error budgets
Either charge maintenance to the error budget or formally exclude it via a maintenance window; each trades honesty against fairness.
Bind mounts versus named volumes
A bind mount maps a host path into the container (great for live source in dev); a named volume is Docker-managed storage decoupled from the host layout (ideal for database data).
Block storage availability across AZ failure
Block volumes are AZ-bound, so use snapshots, synchronous replication, or app-level replication, trading cost for lower RTO/RPO.
How would you block merges when PR coverage drops 2%?
Upload coverage to Codecov, set a project status threshold of 2, and require the check in branch protection.
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