Everything in Docker & Kubernetes, page 4
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.
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.
The sidecar proxy pattern in a mesh
A proxy container shares the pod, all in/out traffic is redirected through it, so policy and telemetry apply without code changes.
What a service mesh solves
It adds traffic management, security via mTLS, and observability at the network layer through sidecars, beyond what plain Kubernetes offers.
Preventing split-brain in HA Operators
Run active-passive replicas, only the leader reconciles, election uses a Lease object renewed under a TTL.
Mutating vs Validating webhooks with an Operator
Mutating runs first to inject defaults or sidecars, validating runs after to reject bad specs, both keyed to your CRD.
Keeping operator .status accurate under failures
Status can lag or go stale during partitions and crashes; make reconcile idempotent, observe true state each loop, use conditions and observedGeneration, handle conflicts.
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