Before You Start v1.26.1
Before we get started, it is essential to go over some terminology that is specific to Kubernetes and PostgreSQL.
Kubernetes terminology
Node : 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).
Postgres Node
: A Postgres node is a Kubernetes worker node dedicated to running PostgreSQL
workloads. This is achieved by applying the node-role.kubernetes.io label and
taint, as proposed by EDB Postgres® AI for CloudNativePG™ Cluster.
It is also referred to as a postgres node.
Pod : 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.
Service : 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.
Secret : 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.
Storage Class : 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.
Persistent Volume : 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) is a persistent volume that exists only on the particular node where the pod that uses it is running.
Persistent Volume Claim : 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.
Namespace : 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.
RBAC : 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.
CRD : A custom resource definition (CRD) is an extension of the Kubernetes API and allows developers to create new data types and objects, called custom resources.
Operator : 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
: kubectl is the command-line tool used to manage a Kubernetes cluster.
EDB Postgres® AI for CloudNativePG™ Cluster requires a Kubernetes version supported by the community. Please refer to the "Supported releases" page for details.
PostgreSQL terminology
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 EDB Postgres® AI for CloudNativePG™ Cluster 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, EDB Postgres® AI for CloudNativePG™ Cluster performs administrative tasks
by connecting to the postgres database as the postgres user via peer
authentication over the local Unix Domain Socket.
WAL : Write-Ahead Logging (WAL) is a standard method for ensuring data integrity in database management systems.
PVC group
: A PVC group in EDB Postgres® AI for CloudNativePG™ Cluster' 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).
Cloud terminology
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.
What to do next
Now that you have familiarized with the terminology, you can decide to test EDB Postgres® AI for CloudNativePG™ Cluster on your laptop using a local cluster before deploying the operator in your selected cloud environment.