Project: CloudNativePG (App Definition and Development / Database)
File: before_you_start.md

Before we get started, it is essential to go over some terminology that is specific to Kubernetes and PostgreSQL. : A node is a worker machine in Kubernetes, either virtual or physical, where all services necessary to run pods are managed by the control plane node(s). : A pod is the smallest computing unit that can be deployed in a Kubernetes cluster and is composed of one or more containers that share network and storage. : A service is an abstraction that exposes as a network service an application that runs on a group of pods and standardizes important features such as service discovery across applications, load balancing, failover, and so on. : A secret is an object that is designed to store small amounts of sensitive data such as passwords, access keys, or tokens, and use them in pods. : A storage class allows an administrator to define the classes of storage in a cluster, including provisioner (such as AWS EBS), reclaim policies, mount options, volume expansion, and so on. : A persistent volume (PV) is a resource in a Kubernetes cluster that represents storage that has been either manually provisioned by an administrator or dynamically provisioned by a storage class controller. A PV is associated with a pod using a persistent volume claim and its lifecycle is independent of any pod that uses it. Normally, a PV is a network volume, especially in the public cloud. A [local persistent volume (LPV)](https://kubernetes.io/docs/concepts/storage/volumes/#local) is a persistent volume that exists only on the particular node where the pod that uses it is running. : A persistent volume claim (PVC) represents a request for storage, which might include size, access mode, or a particular storage class. Similar to how a pod consumes node resources, a PVC consumes the resources of a PV. : A namespace is a logical and isolated subset of a Kubernetes cluster and can be seen as a virtual cluster within the wider physical cluster. Namespaces allow administrators to create separated environments based on projects, departments, teams, and so on. : Role Based Access Control (RBAC), also known as role-based security, is a method used in computer systems security to restrict access to the network and resources of a system to authorized users only. Kubernetes has a native API to control roles at the namespace and cluster level and associate them with specific resources and individuals. : A custom resource definition (CRD) is an extension of the Kubernetes API and allows developers to create new data types and objects, *called custom

: An operator is a custom resource that automates those steps that are normally performed by a human operator when managing one or more applications or given services. An operator assists Kubernetes in making sure that the resource's defined state always matches the observed one. : `kubectl` is the command-line tool used to manage a Kubernetes cluster. CloudNativePG requires a Kubernetes version supported by the community. Please refer to the page for details. Instance : A Postgres server process running and listening on a pair "IP address(es)" and "TCP port" (usually 5432). Primary : A PostgreSQL instance that can accept both read and write operations. Replica : A PostgreSQL instance replicating from the only primary instance in a cluster and is kept updated by reading a stream of Write-Ahead Log (WAL) records. A replica is also known as standby or secondary server. PostgreSQL relies on physical streaming replication (async/sync) and file-based log shipping (async). Hot Standby : PostgreSQL feature that allows a replica to accept read-only workloads. Cluster : To be intended as High Availability (HA) Cluster: a set of PostgreSQL instances made up by a single primary and an optional arbitrary number of replicas. Replica Cluster : A CloudNativePG `Cluster` that is in continuous recovery mode from a selected PostgreSQL cluster, normally residing outside the Kubernetes cluster. It is a feature that enables multi-cluster deployments in private, public, hybrid, and multi-cloud contexts. Designated Primary : A PostgreSQL standby instance in a replica cluster that is in continuous recovery from another PostgreSQL cluster and that is designated to become primary in case the replica cluster becomes primary. Superuser : In PostgreSQL a superuser is any role with both `LOGIN` and `SUPERUSER` privileges. For security reasons, CloudNativePG performs administrative tasks by connecting to the `postgres` database as the `postgres` user via `peer` authentication over the local Unix Domain Socket. : Write-Ahead Logging (WAL) is a standard method for ensuring data integrity in database management systems. PVC group : A PVC group in CloudNativePG's terminology is a group of related PVCs belonging to the same PostgreSQL instance, namely the main volume containing the PGDATA (`storage`) and the volume for WALs (`walStorage`).| Region : A region in the Cloud is an isolated and independent geographic area organized in availability zones. Zones within a region have very little round-trip network latency. Zone : An availability zone in the Cloud (also known as zone) is an area in a region where resources can be deployed. Usually, an availability zone corresponds to a data center or an isolated building of the same data center. Now that you have familiarized with the terminology, you can decide to before deploying the operator in your selected cloud environment.