docs: add architecture concept

README.md

@@ -13,7 +13,11 @@ Use Elasticell as Redis. You can replace Redis with Elasticell to power your app
 Grow Elasticell as your business grows. You can increase the capacity simply by adding more machines.
 
 - __Strong consistent persistence storage__
-You can think of Elasticell as a single-machine NoSQL which provide 7*24 service and has zero downtime. Elasticell put your data on multiple machines as replication without worrying about consistency. Elasticell makes your application use redis as a database and not just only the cache.
+Elasticell put your data on multiple machines as replication without worrying about consistency. Elasticell makes your application use redis as a database and not just only the cache.
+
+- __High availability__
+All of the three components, PD, Cell and Proxy, can tolerate the failure of some instances without impacting the availability of the entire cluster.
+
 
 ## Roadmap
 

docs/ROADMAP.md

@@ -6,6 +6,7 @@ This document defines the roadmap for Elasticell development.
 - [x] Multi-Raft
 - [x] Redis protocol
 - [x] RocksDB 
+- [ ] Go,Java,Python redis lib
 - [ ] Prometheus
 - [ ] PD admin UI
 - [ ] Index

docs/architecture/concept.md

@@ -0,0 +1,40 @@
+## Concept
+To better understand Elasticell’s architecture, you need to understand the Elasticell concept.
+
+### Store
+Store is a service that runs on a single disk. A store manage many cells, and provide data storage for cells, and dispatch messages to cells.
+
+### Cell
+A cell manage some data in range of [start, end), every cell has some replication on different stores, we called these replications Peer. All cell replications with has same id makes up a raft group. Cell's peer maybe scheduled by PD move to another store, or removed from the store.
+
+A cell has three meta data:
+
+1. ID, The uniquely identifies of a cell
+
+2. Data range, Decide which data is managed by the cell
+
+3. Peers, Cell replications
+
+4. Epoch, The version of the cell, it will increase every time the peers changes or cell split
+
+In the raft group, number of cell replications needs to be set an odd number. Usually it is recommended to set to 3 at least.
+
+### PD (Placement Driver)
+PD is the managing component of the entire cluster and is in charge of the following two operations:
+
+1. Storing the metadata of the cluster such as the cell location of a specific key.
+
+2. Scheduling and load balancing cells in the store cluster, including but not limited to data migration and Raft group leader transfer.
+
+As a cluster, PD needs to be deployed to an odd number of nodes. Usually it is recommended to deploy to 3 online nodes at least.
+
+### Proxy (optional component)
+The Proxy server is used for proxy the read and write operation for external application. The proxy is in charge of the following three operations:
+
+1. Sync cells metadata to local from PD
+
+2. Receive read and write operation from external application, and forward these operations to the correct store according to metadata and the key.
+
+3. Receive the response from the store, and forwarding it to the external application. Resynchronize the metadata from PD when an raft error occurs, and retry forward the operation.
+
+The proxy is stateless and can be scaled.

docs/architecture/index.md

@@ -0,0 +1,18 @@
+## Architecture
+To better understand Elasticell’s features, you need to understand the Elasticell architecture.
+
+![architecture](../imgs/architecture.png)
+
+The Elasticell has threee components: PD server, cell server, and proxy server.
+
+### __Compatible with Redis protocol__
+Use Elasticell as Redis. You can replace Redis with Elasticell to power your application without changing a single line of code in most cases([unsupport-redis-commands](./unsupport-command.md)).
+
+### __Horizontal scalability__
+Grow Elasticell as your business grows. You can increase the capacity simply by adding more machines.
+
+### __Strong consistent persistence storage__
+Elasticell put your data on multiple machines as replication without worrying about consistency. Elasticell makes your application use redis as a database and not just only the cache.
+
+### __High availability__
+All of the three components, PD, Cell and Proxy, can tolerate the failure of some instances without impacting the availability of the entire cluster.

docs/index.md

@@ -2,11 +2,14 @@
 
 Elasticell is a distributed NoSQL database with strong consistency and reliability.
 
-- __Compatible with Redis protocol__
+### __Compatible with Redis protocol__
 Use Elasticell as Redis. You can replace Redis with Elasticell to power your application without changing a single line of code in most cases([unsupport-redis-commands](./unsupport-command.md)).
 
-- __Horizontal scalability__
+### __Horizontal scalability__
 Grow Elasticell as your business grows. You can increase the capacity simply by adding more machines.
 
-- __Strong consistent persistence storage__
-You can think of Elasticell as a single-machine NoSQL which provide 7*24 service and has zero downtime. Elasticell put your data on multiple machines as replication without worrying about consistency. Elasticell makes your application use redis as a database and not just only the cache.
+### __Strong consistent persistence storage__
+Elasticell put your data on multiple machines as replication without worrying about consistency. Elasticell makes your application use redis as a database and not just only the cache.
+
+### __High availability__
+All of the three components, PD, Cell and Proxy, can tolerate the failure of some instances without impacting the availability of the entire cluster.

mkdocs.yml

@@ -7,7 +7,7 @@ pages:
   - Quick Start: user-guide/quick-start.md
   - Installation: user-guide/installation.md
   - Configuation: user-guide/configuration.md
-- Architecture:
+- Architecture: architecture/index.md
   - Concept: architecture/concept.md
   - PD: architecture/pd.md
   - Cell: architecture/cell.md