[prometheus] create prometheus exporter skeleton

gateway/Roverfile.lock

@@ -18,6 +18,7 @@ luassert 1.7.10-0||testing
 luasystem 0.2.1-0||testing
 markdown 0.33-1||development
 mediator_lua 1.1.2-0||testing
+nginx-lua-prometheus 0.20171117-4||production
 penlight 1.5.4-1||production,development,testing
 router 2.1-0||production
 say 1.3-1||testing

gateway/apicast-scm-1.rockspec

@@ -20,6 +20,7 @@ dependencies = {
    'liquid',
    'argparse',
    'penlight',
+   'nginx-lua-prometheus',
 }
 build = {
    type = "make",

gateway/conf/nginx.conf.liquid

@@ -106,6 +106,19 @@ http {
     {% include "conf.d/apicast.conf" %}
   }
 
+  {% if port.metrics %}
+    lua_shared_dict prometheus_metrics 16M;
+    server {
+      access_log off;
+      listen {{ port.metrics }} default_server;
+      server_name _;
+
+      location /metrics {
+        content_by_lua_block { require('apicast.executor'):metrics() }
+      }
+    }
+  {% endif %}
+
   {% for file in "sites.d/*.conf" | filesystem %}
     {% include file %}
   {% endfor %}

gateway/config/development.lua

@@ -28,5 +28,6 @@ return {
     lua_code_cache = 'on',
     configuration_loader = 'lazy',
     configuration_cache = 0,
-    configuration = data_url('application/json', configuration)
+    configuration = data_url('application/json', configuration),
+    port = { metrics = 9100 },
 }

gateway/src/apicast/executor.lua

@@ -9,6 +9,7 @@ require('apicast.loader') -- to load code from deprecated paths
 local PolicyChain = require('apicast.policy_chain')
 local policy = require('apicast.policy')
 local linked_list = require('apicast.linked_list')
+local prometheus = require('apicast.prometheus')
 
 local setmetatable = setmetatable
 
@@ -58,4 +59,11 @@ function _M:context(phase)
     return shared_build_context(self)
 end
 
+local metrics = _M.metrics
+--- Render metrics from all policies.
+function _M:metrics(...)
+    metrics(self, ...)
+    return prometheus:collect()
+end
+
 return _M.new(PolicyChain.default())

gateway/src/apicast/policy.lua

@@ -13,7 +13,7 @@ local PHASES = {
     'rewrite', 'access',
     'content', 'balancer',
     'header_filter', 'body_filter',
-    'post_action',  'log'
+    'post_action',  'log', 'metrics',
 }
 
 local setmetatable = setmetatable

gateway/src/apicast/prometheus.lua

@@ -0,0 +1,20 @@
+local prometheus = require('nginx.prometheus')
+
+local dict = 'prometheus_metrics'
+
+if ngx.shared[dict] then
+  local init = prometheus.init(dict)
+
+  local metrics = { }
+  local __call = function(_, type, name, ...)
+    if not metrics[name] then
+      metrics[name] = init[type](init, name, ...)
+    end
+
+    return metrics[name]
+  end
+
+  return setmetatable({ }, { __call = __call, __index = init })
+else
+  return function() end
+end