Top Docker in Interviews — Jenkins CI/CD Focused Guide (2026) with clear, practical answers for 2026 interviews.
How does Docker fit into a Jenkins pipeline?
Jenkins builds a Docker image, runs tests in a container, pushes the image to a registry, and deploys it — giving reproducible, isolated build/test environments.
How do you build a Docker image in a Jenkinsfile?
A stage runs `docker build -t app:$BUILD_NUMBER .`, then `docker push` after login; agents can also run inside Docker containers via the `docker` agent directive.
How do you tag images in CI?
Immutable tags (build number or git SHA) for traceability, plus a moving tag (latest/env) — never deploy by `latest` alone.
How do you keep Jenkins Docker builds fast?
Layer caching, multi-stage builds, a shared registry cache, and pinning base image versions.
How do you handle secrets in Jenkins + Docker?
Jenkins Credentials + build-args/secrets at build time, never baked into the image; use runtime env/secret stores for deploy.
Blue/green or canary with Docker images?
Deploy the new image alongside the old, shift traffic gradually (via the orchestrator/ingress), and roll back by re-pointing to the previous image tag.
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