Basic Concepts

DCS Instance

An instance is the minimum resource unit provided by DCS.

You can select the Redis or Memcached cache engine. Instance types can be single-node, master/standby, or cluster. For each instance type, multiple specifications are available.

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

Public Network Access

A Redis 3.0 instance with an Elastic IP (EIP) can be accessed on a client using the EIP. A Redis 4.0/5.0/6.0 instance can be accessed in public using Elastic Load Balance (ELB).

Stunnel is used to encrypt communication content in public network access. The network delay is slightly higher than that in the VPC, so public network access is suitable for local commissioning in the development phase.

For details, see the public access instructions.

Password-Free Access

DCS instances can be accessed in a 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. To ensure data security, you are not allowed to enable password-free access for instances enabled with public network access.

For details, see Configuring the Redis Password (Modifying the Redis Instance Access Mode).

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 after the instance is created.

For details, see Viewing Instance Details.

Cross-AZ Deployment

Master/Standby, cluster, and read/write splitting 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 an instance, you can select a primary AZ and a standby AZ.

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 distributed to 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 of 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.