Codis：A Distributed Redis Solution（codisredis）

Redis is a popular high performance in-memory data storage system. It has been widely adopted in many applications, ranging from web applications, to messaging systems and caching systems. It provides an advanced key-value data store with support for lists, hashes and sets, along with robust atomic operations and fast data manipulation capabilities.

However, the problem with Redis is that its single-instance nature limits scalability and fails to provide proper availability. This is where Codis, a distributed Redis solution, comes in.

Codis is an open-source community project initiated by Douban, one of the largest online providers of media and entertainment in China. It was developed to address scalability and availability issues that arise from running Redis in a single instance. The system was designed from the ground up to be robust, reliable, and highly fault tolerant.

Codis functions as a layer between applications and Redis databases, allowing for a more distributed and scalable implementation. It uses a proxy layer and a coordinator layer for scalability and availability. The proxy layer contains logical nodes called masters and slaves. The master is responsible for managing the read/write requests from the clients, while the slaves replicate data from the master and respond to read requests from the applications.

The coordinator layer, on the other hand, provides automation for master/slave topologies and data sharding. It is responsible for how data is migrated across different nodes, and provides a unified way to manage, configure and monitor the proxy layer.

The combination of the two layers provides the necessary scalability to Redis that was not previously possible. Its proxy layer allows for a horizontal scaling of the Redis cluster in order to handle increases in load and throughput, while its coordinator layer provides an automated way to scale and balance data across different nodes.

In addition to scalability, Codis also provides several appealing features such as TLS/SSL encryption, multi-tenancy support, high availability, and dashboard to view metrics.

To summarize, Codis is a distributed Redis solution that allows users to utilize a more scalable and maintainable Redis cluster. It comes with a variety of features and tools to afford greater control and visibility over the Redis cluster. It has been adopted by many large organizations, owing to its ability to provide improved scalability and availability for Redis.