feat(datadog): add route-level constant_tags support

`constant_tags` are already supported at the plugin configuration level.
However, sometimes different values may be required for each route, but
this was previously not possible.

For example, if some routes are owned by team A and some routes by team
B, they could add `constant_tags: ["owner:team_a"]` or
`constant_tags: ["owner:team_b"]` to each route, and would then be able
to group metrics by team on Datadog.

Author: deiwin

apisix/plugins/datadog.lua

@@ -39,7 +39,12 @@ local schema = {
     properties = {
         prefer_name = {type = "boolean", default = true},
         include_path = {type = "boolean", default = false},
-        include_method = {type = "boolean", default = false}
+        include_method = {type = "boolean", default = false},
+        constant_tags = {
+            type = "array",
+            items = {type = "string"},
+            default = {}
+        }
     }
 }
 
@@ -82,6 +87,12 @@ local function generate_tag(entry, const_tags)
         tags = {}
     end
 
+    if entry.constant_tags and #entry.constant_tags > 0 then
+        for _, tag in pairs(entry.constant_tags) do
+            core.table.insert(tags, tag)
+        end
+    end
+
     if entry.route_id and entry.route_id ~= "" then
         core.table.insert(tags, "route_name:" .. entry.route_id)
     end
@@ -261,6 +272,10 @@ function _M.log(conf, ctx)
         entry.method = ctx.var.method
     end
 
+    if conf.constant_tags and #conf.constant_tags > 0 then
+        entry.constant_tags = core.table.clone(conf.constant_tags)
+    end
+
     if batch_processor_manager:add_entry(conf, entry) then
         return
     end

docs/en/latest/plugins/datadog.md

@@ -41,11 +41,12 @@ This Plugin provides the ability to push metrics as a batch to the external Data
 
 ## Attributes
 
-| Name           | Type    | Required | Default | Valid values | Description                                                                            |
-| -------------- | ------- | -------- | ------- | ------------ | -------------------------------------------------------------------------------------- |
-| prefer_name    | boolean | False    | true    | [true,false] | When set to `false`, uses Route/Service ID instead of name (default) with metric tags. |
-| include_path   | boolean | False    | false   | [true,false] | When set to `true`, includes the path pattern in metric tags.                          |
-| include_method | boolean | False    | false   | [true,false] | When set to `true`, includes the HTTP method in metric tags.                           |
+| Name           | Type    | Required | Default | Valid values | Description                                                                                                      |
+| -------------- | ------- | -------- | ------- | ------------ | ---------------------------------------------------------------------------------------------------------------- |
+| prefer_name    | boolean | False    | true    | [true,false] | When set to `false`, uses Route/Service ID instead of name (default) with metric tags.                           |
+| include_path   | boolean | False    | false   | [true,false] | When set to `true`, includes the path pattern in metric tags.                                                    |
+| include_method | boolean | False    | false   | [true,false] | When set to `true`, includes the HTTP method in metric tags.                                                     |
+| constant_tags  | array   | False    | []      |              | Static tags to embed into all metrics generated by this route. Useful for grouping metrics over certain signals. |
 
 This Plugin supports using batch processors to aggregate and process entries (logs/data) in a batch. This avoids the need for frequently submitting the data. The batch processor submits data every `5` seconds or when the data in the queue reaches `1000`. See [Batch Processor](../batch-processor.md#configuration) for more information or setting your custom configuration.
 

t/plugin/datadog.t

@@ -538,7 +538,7 @@ message received: apisix\.egress\.size:[\d]+\|ms\|#source:apisix,route_name:data
 
 
 
-=== TEST 11: testing behaviour with include_path and include_method
+=== TEST 11: testing behaviour with include_path, include_method, and route level constant_tags
 --- apisix_yaml
 routes:
   - uri: /articles/*/comments
@@ -552,6 +552,9 @@ routes:
         max_retry_count: 0
         include_path: true
         include_method: true
+        constant_tags:
+          - route_tag1:foo
+          - route_tag2:bar
       proxy-rewrite:
         uri: /opentracing
 #END
@@ -563,10 +566,10 @@ opentracing
 --- grep_error_log eval
 qr/message received: apisix(.+?(?=, ))/
 --- grep_error_log_out eval
-qr/message received: apisix\.request\.counter:1\|c\|#source:apisix,route_name:datadog,path:\/articles\/\*\/comments,method:GET,balancer_ip:[\d.]+,response_status:200,scheme:http
-message received: apisix\.request\.latency:[\d.]+\|h\|#source:apisix,route_name:datadog,path:\/articles\/\*\/comments,method:GET,balancer_ip:[\d.]+,response_status:200,scheme:http
-message received: apisix\.upstream\.latency:[\d.]+\|h\|#source:apisix,route_name:datadog,path:\/articles\/\*\/comments,method:GET,balancer_ip:[\d.]+,response_status:200,scheme:http
-message received: apisix\.apisix\.latency:[\d.]+\|h\|#source:apisix,route_name:datadog,path:\/articles\/\*\/comments,method:GET,balancer_ip:[\d.]+,response_status:200,scheme:http
-message received: apisix\.ingress\.size:[\d]+\|ms\|#source:apisix,route_name:datadog,path:\/articles\/\*\/comments,method:GET,balancer_ip:[\d.]+,response_status:200,scheme:http
-message received: apisix\.egress\.size:[\d]+\|ms\|#source:apisix,route_name:datadog,path:\/articles\/\*\/comments,method:GET,balancer_ip:[\d.]+,response_status:200,scheme:http
+qr/message received: apisix\.request\.counter:1\|c\|#source:apisix,route_tag1:foo,route_tag2:bar,route_name:datadog,path:\/articles\/\*\/comments,method:GET,balancer_ip:[\d.]+,response_status:200,scheme:http
+message received: apisix\.request\.latency:[\d.]+\|h\|#source:apisix,route_tag1:foo,route_tag2:bar,route_name:datadog,path:\/articles\/\*\/comments,method:GET,balancer_ip:[\d.]+,response_status:200,scheme:http
+message received: apisix\.upstream\.latency:[\d.]+\|h\|#source:apisix,route_tag1:foo,route_tag2:bar,route_name:datadog,path:\/articles\/\*\/comments,method:GET,balancer_ip:[\d.]+,response_status:200,scheme:http
+message received: apisix\.apisix\.latency:[\d.]+\|h\|#source:apisix,route_tag1:foo,route_tag2:bar,route_name:datadog,path:\/articles\/\*\/comments,method:GET,balancer_ip:[\d.]+,response_status:200,scheme:http
+message received: apisix\.ingress\.size:[\d]+\|ms\|#source:apisix,route_tag1:foo,route_tag2:bar,route_name:datadog,path:\/articles\/\*\/comments,method:GET,balancer_ip:[\d.]+,response_status:200,scheme:http
+message received: apisix\.egress\.size:[\d]+\|ms\|#source:apisix,route_tag1:foo,route_tag2:bar,route_name:datadog,path:\/articles\/\*\/comments,method:GET,balancer_ip:[\d.]+,response_status:200,scheme:http
 /