doc: add yaml design doc (#5)

* doc: add yaml design doc

* doc: add EOL

* doc: change baidu -> foo

* doc: add EOL for doc/yaml_struct.md

* doc: fix md style

README.md

@@ -11,4 +11,5 @@ We can use `yaml` to define the proxy behavior of APISIX
 
 ## DISCUSS
 Here are some examples of `yaml` and we can add comments here.
-https://github.com/apache/apisix-control-plane/issues/3
+https://github.com/apache/apisix-control-plane/issues/3
+We can also submit a PR to modify this [document](doc/yaml_struct.md).

doc/yaml_struct.md

@@ -0,0 +1,234 @@
+## Currently, 4 types are defined, namely
+
+1.Gateway
+2.Traffic distribution rules
+3.Define the target service
+4.Plug-in extension
+
+### Gateway
+
+For edge traffic, extract the host separately and define a Gateway type
+
+```yaml
+kind:Gateway
+name: foo-gw
+servers:
+ - port:
+     number: 80
+     name: http
+     protocol: HTTP
+   hosts:
+   - "a.foo.com"
+   - "b.foo.com"
+```
+
+|  object/field   | describition |
+|  ----  | ----  |
+| Gateway  | the type for Edge traffic  |
+| Gateway.servers  | Define edge traffic service list  |
+| Gateway.servers.port  | the port for service  |
+| Gateway.servers.port.protocol  | Specify protocol  |
+| Gateway.servers.hosts  | List of domain names that a certain service can accept  |
+
+### Define traffic distribution rules
+
+```yaml
+kind: Rule
+name: xxx-rules
+hosts:
+- "a.foo.com"
+gateways:
+- foo-gw
+http:
+- route:
+ - destination:
+     port: 28002
+     host: foo-server
+     subset: foo-v1
+     weight: 10
+ label：
+    app: foo
+    version: v1
+  match:
+  - headers:
+     product_id:
+       exact: v1
+- route:
+  - destination:
+       port: 28002
+       host: foo-server
+       subset: v2
+  label:
+    app: foo
+    version: v2
+
+```
+
+|  object/field   | describition |
+|  ----  | ----  |
+|  Rule  | the rule type for traffic |
+|  Rule.hosts  | Specify the list of accepted hosts |
+|  Rule.gateways  | Specify which gateway it belongs to, receive traffic from the edge gateway |
+|  Rule.http  | Specify the HTTP protocol (similar to other protocols) |
+|  Rule.http.route  | define route|
+|  Rule.http.match  | Conditions for hitting the route|
+|  Rule.http.route.destination  | Target service definition|
+
+### Define the target service
+
+```yaml
+kind: destinations
+name: foo-dest
+host: foo-server
+subsets:
+- name: foo-v1
+  ips：
+  - 127.0.0.1
+  - 127.0.0.2
+- name: v2
+  selector:
+    labels:
+      tag: v2
+
+```
+
+|  object/field   | describition |
+|  ----  | ----  |
+|  destinations  | Target service |
+| destinations.host | Target service internal host |
+| destinations.subsets | Target service collection |
+
+### Plug-in extension
+
+The logic of the plugin itself is not defined here, only known plugins will be referenced here
+
+```yaml
+kind：Plugin
+selector：
+  labels：
+     app: foo
+sort:
+- name: limit-count
+  conf:
+      max：100
+- name: prometheus
+  conf:
+     ...schema..
+
+```
+
+### A complete demo
+
+1. Use APISIX Admin API
+
+```shell
+curl -XPUT http://127.0.0.1:9080/apisix/admin/routes/1 -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -d '
+{
+    "desc": "test_route",
+    "uris": [
+        "/*"
+    ],
+    vars:[
+        ["arg_name", "==", "json"],
+        ["arg_age", ">", "18"]
+    ],
+    "hosts": [
+        "foo.com"
+    ],
+    "upstream": {
+        "type": "roundrobin",
+        "nodes": {
+            "127.0.0.1:8080": 10
+        },
+        "timeout": {
+            "connect": 6000,
+            "send": 6000,
+            "read": 6000
+        },
+        "enable_websocket": false
+    },
+    "plugins":{
+    	"prometheus":{},
+    	"proxy-rewrite":{
+    		"uri": "/test/home.html",
+            "scheme": "http",
+            "host": "foo.com",
+            "headers": {
+                "X-Api-Version": "v1",
+                "X-Api-Engine": "apisix",
+                "X-Api-useless": ""
+            }
+    	}
+    }
+}'
+
+```
+
+2. Use YAML
+
+```yaml
+kind:Gateway
+name: foo-gw
+servers:
+ - port:
+     number: 80
+     name: http
+     protocol: HTTP
+   hosts:
+   - "foo.com"
+
+-----------------
+
+kind: Rule
+name: foo-rules
+hosts:
+- "foo.com"
+gateways:
+- foo-gw
+http:
+- route:
+  - destination:
+       port: 8080
+       host: foo-server
+       subset: foo-v1
+    label：
+      app: foo
+      version: v1
+  match:
+  - args:
+     name:
+       exact: "json"
+     age:
+       Greater: 18
+  - uri:
+      prefix: "/"
+-------------------
+
+kind: destinations
+name: foo-dest
+host: foo-server
+subsets:
+- name: foo-v1
+  ips：
+  - 127.0.0.1
+
+-------------------
+
+kind：Plugin
+selector：
+  labels：
+     app: foo
+sort:
+- name: proxy-rewrite
+  conf:
+    uri: "/test/home.html"
+    scheme: "http"
+    host: "foo.com"
+    headers:
+      X-Api-Version: "v1"
+      X-Api-Engine: "apisix"
+      X-Api-useless: ""
+- name: prometheus
+
+```
+