Understanding clusters - Amazon DocumentDB

Understanding clusters

Amazon DocumentDB separates compute and storage, and offloads data replication and backup to the cluster volume. A cluster volume provides a durable, reliable, and highly available storage layer that replicates data six ways across three Availability Zones. Replicas enable higher data availability and read scaling. Each cluster can scale up to 15 replicas.

Noun Description API Operations (Verbs)

Cluster

Consists of one or more instances and a cluster storage volume that manages the data for those instances.

create-db-cluster

delete-db-cluster

describe-db-clusters

modify-db-cluster

Instance

Reading and writing data to the cluster storage volume is done via instances. In a given cluster, there are two types of instances: primary and replica. A cluster always has one primary instance and can have 0–15 replicas.

create-db-instance

delete-db-instance

describe-db-instances

modify-db-instance

describe-orderable-db-instance-options

reboot-db-instance

Cluster volume

A virtual database storage volume that spans three Availability Zones, with each Availability Zone having two copies of the cluster data.

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Primary instance

Supports both read and write operations, and performs all data modifications to the cluster volume. Each cluster has one primary instance.

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Replica instance

Supports only read operations. Each Amazon DocumentDB cluster can have up to 15 replica instances in addition to the primary instance. Multiple replicas distribute the read workload. By locating replicas in separate Availability Zones, you can also increase database availability.

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Cluster endpoint

An endpoint for an Amazon DocumentDB cluster that connects to the current primary instance for the cluster. Each Amazon DocumentDB cluster has a cluster endpoint and one primary instance.

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Reader endpoint

An endpoint for an Amazon DocumentDB cluster that connects to one of the available replicas for that cluster. Each Amazon DocumentDB cluster has a reader endpoint. If there is more than one replica, the reader endpoint directs each connection request to one of the Amazon DocumentDB replicas.

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Instance endpoint

An endpoint for an instance in an Amazon DocumentDB cluster that connects to a specific instance. Each instance in a cluster, regardless of instance type, has its own unique instance endpoint.

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