Intermediate everything in Docker & Kubernetes, page 2
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.
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.
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.
What is a dangling image and how to prune it
A dangling image is an untagged layer (<none>:<none>) orphaned when a tag moves to a rebuilt image; list with docker images -f dangling=true, remove with docker image prune.
Debug a running container with the Docker CLI
Docker inspect for full state and config, docker logs -f to follow output live, docker exec -it <id> sh or bash for an interactive shell.
Multi-stage builds for compiled languages
Build in a stage with the full toolchain, then COPY --from only the artifact into a tiny final base, shrinking image size and attack surface.
Optimize Dockerfile layer caching for npm install
Copying all source first invalidates the npm install layer on any code change; instead copy package.json and lockfile, run npm install, then copy the rest.
Mesh control plane vs data plane availability
The control plane configures and distributes policy; the data plane is the sidecars carrying traffic with cached config, so a brief control-plane outage keeps existing traffic flowing but…
How mounted ConfigMap updates propagate to pods
Kubelet refreshes mounted files within roughly a sync period via an atomic symlink swap, but the app must reload on its own; env-var injection never updates.
Image signing with Cosign vs trusting a digest
A digest proves content has not changed but not who produced it; Cosign cryptographically signs the digest so a verified key proves provenance, and policies enforce it at admission.
Docker layers and build cache efficiency
Each instruction makes a content-addressed read-only layer stacked by a union FS; shared layers are pushed/pulled once, and ordering the Dockerfile so volatile steps come last maximizes cache reuse.
Scaling on queue length with the HPA
Expose queue length through an external metrics adapter behind the metrics API, point the HPA at that external metric with a target per pod; KEDA packages this.
Impact of losing etcd quorum
Without quorum etcd goes read-only-ish and the API server cannot persist writes, so scheduling and changes stall, but kubelets keep running existing pods.
Container registries: public vs private
A registry stores and serves versioned image layers by digest; public registries are open and rate-limited, private ones add access control, scanning, signing and network isolation.
What makes a process a container to the kernel
Namespaces isolate and cgroups limit, but also capabilities, seccomp filters, mount/pivot_root for the rootfs, and SELinux/AppArmor labels.
Istio Gateway vs Kubernetes Ingress
Ingress is a simple built-in L7 entry abstraction; an Istio Gateway configures only ports and hosts at the edge while VirtualServices do routing, unlocking mesh features.
Guardrails for GitOps sync outages
Pre-merge schema validation, dry-run, policy gates and review; post-merge progressive sync, health checks with automated rollback, and pruning controls.
Retries and circuit breaking in a mesh
Configure bounded retries with timeouts for transient errors, and a circuit breaker via outlier detection plus connection-pool limits to shed load from a failing dependency.
How a service mesh enables automatic mTLS
The control plane issues short-lived workload certificates, sidecars present them, both sides verify identity and encrypt the channel.
Canary release with Istio traffic splitting
DestinationRule defines subsets by label, VirtualService routes weighted 90/10 to those subsets, then shift weights as the canary proves healthy.
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