What Is DCS?

Distributed Cache Service (DCS) is an online, distributed, in-memory cache service compatible with Redis and Memcached. It is reliable, scalable, usable out of the box, and easy to manage, meeting your requirements for high read/write performance and fast data access.

Usability out of the box
DCS provides single-node, master/standby, and cluster instances with specifications ranging from 128 MB to 1024 GB. DCS instances can be created with just a few clicks on the console, without requiring you to prepare servers.

DCS Redis 4.0 and 5.0 instances are containerized and can be created within seconds.
Security and reliability
Instance data storage and access are securely protected through security management services, including Identity and Access Management (IAM), Virtual Private Cloud (VPC), Cloud Eye, and Cloud Trace Service (CTS).

Master/Standby and cluster instances can be deployed within an availability zone (AZ) or across AZs.
Auto scaling
DCS instances can be scaled up or down online, helping you control costs based on service requirements.
Easy management
A web-based console is provided for you to perform various operations, such as restarting instances, modifying configuration parameters, and backing up and restoring data. RESTful application programming interfaces (APIs) are also provided for automatic instance management.
Online migration
You can create a data migration task on the console to import backup files or migrate data online.

DCS for Redis

Redis is a storage system that supports multiple types of data structures, including key-value pairs. It can be used in such scenarios as data caching, event publication/subscription, and high-speed queuing, as described in Application Scenarios. Redis is written in ANSI C, supporting direct read/write of strings, hashes, lists, sets, sorted sets, and streams. Redis works with an in-memory dataset which can be persisted on disk.

DCS Redis instances can be customized based on your requirements.

**Table 1** DCS Redis instance configuration
Instance type	DCS for Redis provides the following types of instances to suit different service scenarios: Single-node: Suitable for caching temporary data in low reliability scenarios. Single-node instances support highly concurrent read/write operations, but do not support data persistence. Data will be deleted after instances are restarted. Master/Standby: Each master/standby instance runs on two nodes (one master and one standby). The standby node replicates data synchronously from the master node. If the master node fails, the standby node automatically becomes the master node. Proxy Cluster: In addition to the native Redis cluster, a Proxy Cluster instance has proxies and load balancers. Load balancers implement load balancing. Different requests are distributed to different proxies to achieve high-concurrency. Each shard in the cluster has a master node and a standby node. If the master node is faulty, the standby node on the same shard is promoted to the master role to take over services. Redis Cluster: Each Redis Cluster instance consists of multiple shards and each shard includes a master node and multiple replicas (or no replica at all). Shards are not visible to you. If the master node fails, a replica on the same shard takes over services. You can split read and write operations by writing to the master node and reading from the replicas. This improves the overall cache read/write performance.
Instance specification	DCS for Redis provides instances of different specifications, ranging from 128 MB to 1024 GB.
Redis version	DCS instances are compatible with open-source Redis 3.0, 4.0, and 5.0.
Underlying architecture	Standard Redis based on VMs: supports up to 100,000 queries per second (QPS) at a single node.
High availability (HA) and DR	Master/standby and cluster DCS Redis instances can be deployed across AZs in the same region with physically isolated power supplies and networks.

For more information about open-source Redis, visit https://redis.io/.

DCS for Memcached

Memcached is an in-memory key-value caching system that supports read/write of simple strings. It is often used to cache backend database data to alleviate load on these databases and accelerate web applications. For details about its application scenarios, see Memcached Application Scenarios.

In addition to full compatibility with Memcached, DCS for Memcached provides the hot standby and data persistence.

**Table 2** DCS Memcached instance configuration
Instance type	DCS for Memcached provides the following two types of instances to suit different service scenarios: Single-node: Suitable for caching temporary data in low reliability scenarios. Single-node instances support highly concurrent read/write operations, but do not support data persistence. Data will be deleted after instances are restarted. Master/Standby: Each master/standby instance runs on two nodes (one master and one standby). The standby node replicates data synchronously from the master node, but does not support read/write operations. If the master node fails, the standby node automatically becomes the master node.
Memory	Specification of single-node or master/standby DCS Memcached instances: 2 GB, 4 GB, 8 GB, 16 GB, 32 GB, and 64 GB.
HA and DR	Master/Standby DCS Memcached instances can be deployed across AZs in the same region with physically isolated power supplies and networks.