Basic Concepts

DCS Instance

An instance is the minimum resource unit provided by DCS.

DCS supports the Redis cache engine, and single-node, master/standby, and cluster instance types. For each instance type, multiple specifications are available.

For details, see DCS Instance Specifications and DCS Instance Types.

Project

Projects are used to group and isolate OpenStack resources (computing resources, storage resources, and network resources). A project can be a department or a project team. Multiple projects can be created for one account.

Password-Free Access

DCS Redis instances can be accessed in the VPC without passwords. Latency is lower because no password authentication is involved.

You can enable password-free access for instances that do not have sensitive data.

Maintenance Time Window

The maintenance time window is the period when the DCS service team upgrade and maintain the instance.

DCS instance maintenance takes place only once a quarter and does not interrupt services. Even so, you are advised to select a time period when the service demand is low.

When creating an instance, you must specify a maintenance time window, which can be modified on the Basic Information page after the instance is created.

Cross-AZ Deployment

Master/Standby instances are deployed across different AZs with physically isolated power supplies and networks. Applications can also be deployed across AZs to achieve HA for both data and applications.

When creating a master/standby or cluster DCS Redis instance, you can select a standby AZ for the node.

Shard

A shard is a management unit of a cluster DCS Redis instance. Each shard corresponds to a redis-server process. A cluster consists of multiple shards. Each shard has multiple slots. Data is distributedly stored in the slots. The use of shards increases cache capacity and concurrent connections.

Each cluster instance consists of multiple shards. By default, each shard is a master/standby instance with two replicas. The number of shards is equal to the number of master nodes in a cluster instance.

Replica

A replica is a node in a DCS instance. A single-replica instance has no standby node. A two-replica instance has one master node and one standby node. By default, each master/standby instance has two replicas. If the number of replicas is set to three for a master/standby instance, the instance has one master node and two standby nodes. A single-node instance has only one node.