Glossary
The docktionary itself
Every piece of jargon from the rest of the site, in one place. Search, filter by category, or test yourself with flashcards.
57 of 57 terms
Container
A single running process, packaged with everything it needs, isolated from the host.General
Image
A read-only template of stacked layers used to create containers.Docker
Layer
One cached, immutable filesystem diff produced by a single Dockerfile instruction.Docker
Dockerfile
A text file of instructions describing how to build an image.Docker
Registry
A server that stores and serves images, organized into repositories.Docker
Repository
A named collection of related image versions, distinguished by tag.Docker
Tag
A human-readable pointer to a specific image digest, like a git branch for images.Docker
Volume
Persistent storage managed by Docker, independent of any single container's lifecycle.Storage
Bind mount
A host filesystem path mounted directly into a container.Storage
Network
A virtual switch that lets containers discover and talk to each other by name.Networking
Docker Compose
A tool and YAML format for defining and running multi-container applications.Docker
ENTRYPOINT
The fixed executable a container runs; CMD supplies its default arguments.Docker
Multi-stage build
A Dockerfile with several FROM stages, so build tools never ship in the final image.Docker
HEALTHCHECK
A command Docker runs periodically to decide if a container is actually working.Docker
Pod
The smallest deployable unit in Kubernetes — one or more containers sharing network and storage.Kubernetes
Deployment
A controller that keeps a desired number of Pod replicas running and handles rollouts.Kubernetes
ReplicaSet
Ensures a specified number of identical Pod replicas are running at all times.Kubernetes
Service
A stable virtual IP and DNS name that load-balances traffic to a changing set of Pods.Kubernetes
Ingress
HTTP(S) routing rules into cluster Services, usually with host- and path-based rules.Kubernetes
Namespace
A virtual cluster-within-a-cluster used to scope and separate resources.Kubernetes
ConfigMap
Non-secret configuration data injected into Pods as env vars or mounted files.Kubernetes
Secret
Like a ConfigMap, but for sensitive values — base64-encoded, not encrypted, by default.Kubernetes
StatefulSet
Manages Pods that need a stable identity and storage, like databases.Kubernetes
DaemonSet
Ensures one copy of a Pod runs on every (or every matching) node.Kubernetes
Job
Runs Pods to completion for a finite task, retrying on failure.Kubernetes
CronJob
Creates Jobs on a cron schedule.Kubernetes
kubelet
The node agent that makes containers run according to the PodSpecs it's given.Kubernetes
Control plane
The set of components that make cluster-wide decisions: API server, scheduler, controller manager, etcd.Kubernetes
etcd
The distributed key-value store holding all Kubernetes cluster state.Kubernetes
kubectl
The command-line client for talking to a Kubernetes API server.Kubernetes
Helm
A package manager for Kubernetes, bundling manifests into reusable, versioned charts.Kubernetes
Custom Resource Definition (CRD)
Extends the Kubernetes API with your own object types.Kubernetes
Operator
A controller that encodes human operational knowledge to manage a complex app via a CRD.Kubernetes
Persistent Volume (PV)
A piece of cluster storage provisioned ahead of time, independent of any Pod.Storage
Persistent Volume Claim (PVC)
A Pod's request for storage, bound to a matching Persistent Volume.Storage
StorageClass
Describes a "class" of storage a cluster can provision on demand.Storage
CNI (Container Network Interface)
The plugin spec that gives Pods their networking.Networking
NetworkPolicy
Firewall rules for which Pods may talk to which, enforced by the CNI plugin.Networking
Service mesh
A dedicated infrastructure layer (often sidecar proxies) for service-to-service traffic.Networking
Load balancer
Distributes incoming traffic across multiple backend instances.Networking
Horizontal Pod Autoscaler (HPA)
Automatically scales the number of Pod replicas based on observed metrics.Kubernetes
Cluster autoscaler
Adds or removes nodes from a cluster based on whether Pods are pending or nodes are idle.Cloud
Managed Kubernetes
A cloud provider runs and patches your control plane; you manage workloads and (usually) nodes.Cloud
Node pool
A group of cluster nodes sharing the same machine type and configuration.Cloud
Container runtime
The low-level software that actually creates and runs containers on a host.General
cgroups
A Linux kernel feature that limits and accounts for a process group's resource usage.General
Namespaces (kernel)
The Linux kernel primitive that gives a process its own isolated view of the system.General
Orchestration
Automating the deployment, scaling, networking, and healing of many containers.General
Immutable infrastructure
Instead of patching running servers, you replace them with new ones built from an image.General
Sidecar
A helper container that runs alongside the main container in the same Pod.Kubernetes
Init container
Runs to completion before a Pod's main containers start.Kubernetes
Rolling update
Replacing old Pods with new ones gradually, keeping the service available throughout.Kubernetes
Blue-green deployment
Run two full environments and switch traffic from one to the other instantly.General
Canary deployment
Route a small slice of traffic to a new version before rolling it out fully.General
Manifest
A YAML or JSON file declaring the desired state of a Kubernetes object.Kubernetes
Label selector
A query over key-value labels that determines which objects a resource applies to.Kubernetes
Resource requests & limits
Declared CPU/memory a container needs (request) versus the hard cap it may use (limit).Kubernetes