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WebSocket

Background

  • Reverse proxy is one of most popular features of Easegress and it's suitable for many production and development scenarios.

  • In reversed proxy use cases, WebSocket is a widely used protocol for a full-duplex communication solution between client and server. WebSocket relies on TCP.[1]

  • Many reverse proxy support WebSocket,e.g., NGINX[2], Traefik, and so on.

Design

  • The WebSocketProxy is a filter of Easegress, and can be put into a pipeline.
  • Easegress uses github.com/golang/x/net/websocket to implement WebSocketProxy filter.
  1. Spec
  • Pipeline with a WebSocketProxy filter:
name: websocket-pipeline
kind: Pipeline

flow:
- filter: wsproxy

filters:
- kind: WebSocketProxy
  name: wsproxy
  defaultOrigin: https://127.0.0.1/hello
  pools:
  - servers:
    - url: ws:https://127.0.0.1:12345
  • HTTPServer to route traffic to the websocket-pipeline:
name: demo-server
kind: HTTPServer
port: 8080
rules:
- paths:
  - path: /ws
    clientMaxBodySize: -1          # REQUIRED!
    backend: websocket-pipeline

Note: clientMaxBodySize must be -1.

  1. Request sequence

    +--------------+                +--------------+                +--------------+  
|              |  1             |              |   2            |              | 
|   client     +--------------->|  Easegress   +--------------->|  websocket   |
|              |<---------------+              |<---------------+  backend     | 
|              |  4             |              |   3            |              |
+--------------+                +--------------+                +--------------+

  2. Headers

We copy all headers from your HTTP request to websocket backend, except ones used by websocket package to build connection. Based on [3], we also add X-Forwarded-For, X-Forwarded-Host, X-Forwarded-Proto to http headers that send to websocket backend.

note: websocket use Upgrade, Connection, Sec-Websocket-Key, Sec-Websocket-Version, Sec-Websocket-Extensions and Sec-Websocket-Protocol in http headers to set connection.

Example

  1. Send request

    curl --include \
    --no-buffer \
    --header "Connection: Upgrade" \
    --header "Upgrade: websocket" \
    --header "Host: 127.0.0.1:10020" \
    --header "Sec-WebSocket-Key: your-key-here" \
    --header "Sec-WebSocket-Version: 13" \
    https://127.0.0.1:8080/

  2. This request to Easegress will be forwarded to websocket backend ws:https://127.0.0.1:12345.

References

  1. https://datatracker.ietf.org/doc/html/rfc6455
  2. https://www.nginx.com/blog/websocket-nginx/
  3. https://docs.oracle.com/en-us/iaas/Content/Balance/Reference/httpheaders.htm