xDS Overview

The Linux configuration landscape is very fragmented. What can we learn from the success of Envoy's xDS?

1. xDS Overview Stefano Borrelli @stedvendborrelli Sept 2020: Linux COSI project
2. • High-Performance Load Balancer • Feature-rich: L3-L7 proxying, Pluggable filters, etc. • Dynamic configuration via API: • “The universal data plane”
3. Envoy Ecosystem Multiple Control Planes
4. Linux is Fragmented Traditional Traditional Container
5. Traditional
6. Linux is Fragmented Traditional • No standard API • Cloud-init is a separate system • Diverse Init Systems (Systemd, OpenRC, custom) • Diverse communication: API vs. Shell • Push vs. Pull configuration • Kubelet has many OS responsibilities •
7. What can we learn from xDS?
8. xDS Overview • “…a simple API that abstracts the data plane from the control plane.” — Matt Klein • The data plane is meant to be simple. Opinionated decisions are implemented at the control plane. • This decouples envoy from higher-level orchestration. • Use a generic common bootstrap (file), then can subscribe to any number of control planes. https://blog.envoyproxy.io/the-universal-data-plane-api-d15cec7a
9. xDS Overview • Typed Interfaces in Protocol Buffers v3 • Utilizes gRPC: Bi-directional streaming, etc. Also supports JSON/REST Metadata support • Supports static (file-based) and dynamic (streaming gRPC) configurations • Eventually consistent
10. xDS Overview Traditional https://blog.christianposta.com/envoy/guidance-for-building-a-control-plane-to-manage-envoy-proxy-based-infrastructure/ Endpoint Discovery Service (EDS) Cluster Discovery Service (CDS) Route Discovery Service (RDS) Listener Discovery Service (LDS) Health Discovery Service (HDS) Secret Discovery Service (SDS) Aggregated Discovery Service (ADS)
11. Transport Features xDS supports delta and complete (State of the World) updates, allows multiple subscriptions or connection to an aggregated resource server: • State of the World (Basic xDS): SotW, separate gRPC stream for each resource type (DiscoveryRequest/DiscoveryResponse proto3) • Incremental xDS: incremental, separate gRPC stream for each resource type (DeltaDiscoveryRequest/DeltaDiscoveryResponse proto3) • Aggregated Discovery Service (ADS): SotW, aggregate stream for all resource types • Incremental ADS: incremental, aggregate stream for all resource types
12. Native gRPC support for xDS https://github.com/grpc/proposal/blob/master/A27-xds-global-load- balancing.md Replace grpclb Merged into gRPC 1.6 ADS SotW only for now, no plans for incremental for file config
13. xDS Examples • step-sds (how to craft a raw xDS Discovery Response) • Health Discovery Service Protobuf (Distributed Health check) • go-control-plane (How to build an xDS Control Plane)
14. Summary • xDS is a great example of building out a data-plane API • Opportunity for COSI to define core Linux primitives •