Xline

Xline is a geo-distributed KV store for metadata management. It provides the following features:

• Etcd compatible API.
• Geo-distributed friendly deployment.
• Compatible with K8s.

Motivation

With the wide adoption of cloud computing, multi-cloud has become the mainstream IT architecture for enterprise customers. Multi-cloud (or similarly multi-datacenter), however, obstacles data access across different cloud (or data center) providers to some extent. Further, data isolation and data fragmentation resulting from cloud barriers have become impediments to business growth. The biggest challenge of multi-datacenter architecture is how to maintain strong data consistency and ensure high performance in the race condition of multi-datacenter scenario. Traditional single datacenter solutions cannot meet the availability, performance, and consistency requirements of multi-data center scenarios. This project targets the multi-datacenter scenario, aiming to realize a high-performance multi-cloud metadata management solution, which is critical for businesses with geo-distributed and multi-active deployment requirements.

Innovation

Cross-datacenter network latency is the most important factor that impacts the performance of geo-distributed systems, especially when a consensus protocol is used. We know consensus protocols are popular to use to achieve high availability. For instance, Etcd uses the Raft protocol, which is quite popular in recently developed systems.

Although Raft is stable and easy to implement, it takes 2 RTTs to complete a consensus request from the view of a client. One RTT takes place between the client and the leader server, and the leader server takes another RTT to broadcast the message to the follower servers. In a geo-distributed environment, an RTT is quite long, varying from tens of milliseconds to hundreds of milliseconds, so 2 RTTs are too long in such cases.

We adopt a new consensus protocol named CURP to resolve the above issue. Please refer to the paper for a detailed description. The main benefit of the protocol is reducing 1 RTT when contention is not too high. As far as we know, Xline is the first product to use CURP. For more protocol comparison, please refer to the blog

Performance Comparison

We compared Xline with Etcd in a simulated multi-cluster environment. The details of the deployment is shown below.

We compared the performance with two different workloads. One is 1 key case, the other is 100K key space case. Here's the test result.

It's easy to tell Xline has a better performance than Etcd in a geo-distributed multi-cluster environment.

Quick Start

Read the document QUICK_START.md for more details.

Contribute Guide

Read the document CONTRIBUTING.md for more details.

Code of Conduct

Read the document CODE_OF_CONDUCT.md for more details.

Roadmap

• v0.1 ~ v0.2

  • Support all major ETCD APIs
  • Support configuration file
  • Pass validation tests (All the supported etcd APIs and their validation test results can be viewed in VALIDATION_REPORT.md)

• v0.3 ~ v0.5

  • Enable persistent storage
  • Enable snapshot
  • Enable cluster membership change
  • Implement a k8s operator basically

• v0.6 ~ v0.8

  • Enable to export metrics to some monitoring and alerting systems
  • Enable SSL/TLS certificates
  • Provide clients implementing in different languages, like go, python (not determined). [Note: Although the Xline is etcd-compatible, we provide an Xline specific client SDK to users for better performance. Currently this SDK is only in Rust lang, and we plan to extend it to other languages]

• v1.0 ~

  • Enable chaos engineering to validate the system's stability
  • Integration with other CNCF components