Document zuul filters for developers

[spencergibb]

@markfisher please add any specifics you'd like (like the lack of constants that are documented for map keys that you mentioned.)

[markfisher]

I think a detailed description of the RequestContext would be very useful. That should include any map keys that contribute to pre-established behavior as well as a thorough explanation of the way various methods on the context can influence response generation (for example, I seem to notice different behavior based on whether ctx.setResponseBody(..) has been called even if ctx.setResponseStatusCode(..) has been called with a status code that doesn't typically accompany a response body).

[spencergibb]

Mark Fisher [1:20 PM]
I think the most important thing would be to understand exactly what influences the request/response as well as the actual routing.... e.g. the "forward.to" key in the RequestContext and how that path resolves within the context of the current request

Mark Fisher [1:34 PM]
also would be good to have an overview of what's provided by ZuulProxyConfiguration which I believe is what determines most of the details I just mentioned in the last comment

[spencergibb]

Document different clients (OkHttp3, apache http client and ribbon rest client). Note which ribbon properties are only for ribbon restclient. SSL examples as well. See #1446

[spencergibb]

Here is my outline that I'm working on now:

• See https://github.com/Netflix/zuul/wiki/How-it-Works for a general zuul overview
• Describe how installed
  • Controller
  • Plain Servlet (for large files)
• Describe different ribbon http clients
• howto disable filters
• Describe RequestContext
  • link to https://github.com/spring-cloud/spring-cloud-netflix/blob/master/spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/zuul/filters/support/FilterConstants.java[FilterConstants]
• Describe difference between @EnableZuulProxy and @EnableZuulServer
  • Describe installed filters
  • Proxy
  • DiscoveryClient + Properties route locator
    • Refreshed routes
  • PreDecorationFilter
  • RibbonRoutingFilter
  • SimpleHostRoutingFilter
  • Server (no routing)
  • Properties route locator
  • ServletDetectionFilter
  • FormBodyWrapperFilter
  • DebugFilter
  • SendResponseFilter
  • SendForwardFilter
  • SendErrorFilter
• Describe howto write a general pre route determining filter
• Describe howto write a general routing filter
• Describe howto write a general post response manipulation filter
• Describe how errors work

[spencergibb]

Closed via d21d03b7387cdf481304806dd32927ac0b9cc4b1 and 675e4c1031b275af877938c02d5950c91f7fe660