Everything in Docker & Kubernetes, page 4
Dockerfile CMD versus ENTRYPOINT
ENTRYPOINT sets the fixed executable; CMD sets default args or the default command; run-time args override CMD but append to ENTRYPOINT. Use together to make a fixed binary with overridable defaults.
Dockerfile COPY versus ADD
COPY just copies local files; ADD also auto-extracts local tarballs and can fetch remote URLs; prefer COPY for predictability, use ADD for local archive extraction.
Build, tag, and run a container with port mapping
Docker build -t my-app:1.0 . to build and tag; docker run -d -p 8080:80 my-app:1.0 to run detached with host:container port mapping.
Trace a container process's syscalls from the host
Find the host PID via docker inspect or ps, then strace -p that PID from the host, since the container shares the host kernel.
What is the OCI and why do its specs matter?
OCI defines vendor-neutral specs for image format and runtime so any compliant tool interoperates; runc implements the runtime spec; this prevents lock-in.
What is a container vs a VM?
Containers share the host kernel and isolate via namespaces and cgroups; VMs run a full guest OS on a hypervisor; containers are lighter and faster.
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.
Method-aware authorization with Istio policy
An ALLOW policy on user-service granting frontend's principal POST plus the users path, another granting all principals GET; deny is implicit once any ALLOW exists.
Diagnosing latency with distributed tracing
Follow the trace ID across spans, compare per-span durations to find the slow hop, distinguish service time from network and queueing.
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.
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