Transform Graphite tags into Prometheus labels

diff --git a/modules/http/prometheus.lua b/modules/http/prometheus.lua
index 68b491da5cb1efe6254d313b0a87b5dd46241807..094c5f4edd9e320148568fbedfc76b2114538403 100644 (file)
--- a/modules/http/prometheus.lua
+++ b/modules/http/prometheus.lua
@@ -102,7 +102,29 @@ local function serve_prometheus()
        local latency = {}
        local counter = '# TYPE %s counter\n%s %f'
        for k,v in pairs(slist) do
-               k = select(1, k:gsub('%.', '_'))
+               -- Transform Graphite tags into Prometheus labels
+               -- See: https://gitlab.nic.cz/knot/knot-resolver/-/issues/650
+               local k_index, k_len, k_tag = 0, #k, 0
+               k = select(1, k:gsub('.', function (c)
+                       k_index = k_index + 1
+                       if k_tag == 0 then
+                               if c == '.' then return '_' end
+                               if c == ';' then k_tag = 1; return '{' end
+                       elseif k_tag == 1 then
+                               if k_index == k_len then
+                                       if c == '=' then return '=""}'
+                                       else return c .. '"}' end
+                               end
+                               if c == '=' then k_tag = 2; return '="' end
+                       elseif k_tag == 2 then
+                               if k_index == k_len then
+                                       if c == ';' then return '"}'
+                                       else return c .. '"}' end
+                               end
+                               if c == ';' then k_tag = 1; return '",' end
+                       end
+                       return nil
+               end))
                -- Aggregate histograms
                local band = k:match('answer_([%d]+)ms')
                if band then
@@ -112,7 +134,8 @@ local function serve_prometheus()
                -- Counter as a fallback
                else
                        local key = M.namespace .. k
-                       table.insert(render, string.format(counter, key, key, v))
+                       local metric, label = key:match('^([^{]+)(.*)$')
+                       table.insert(render, string.format(counter, metric, metric .. label, v))
                end
        end
        -- Fill in latency histogram