From 45ff6535a0a737880e1f199ca87056272e460d14 Mon Sep 17 00:00:00 2001
From: Sam Saffron <sam.saffron@gmail.com>
Date: Fri, 14 Feb 2020 18:01:07 +1100
Subject: [PATCH] FIX: avoid shelling to get hostname

Previously we were using `hostname` to get hostname, this is slow
and risks orphan processes.

This swaps it with Socket.gethostname which is both faster and more
reliable.

We also now cache it on the PrometheusExporter instance
---
 CHANGELOG                                           |  3 ++-
 lib/prometheus_exporter.rb                          | 11 +++++++++++
 .../instrumentation/active_record.rb                | 13 +------------
 lib/prometheus_exporter/instrumentation/process.rb  | 13 +------------
 test/prometheus_exporter_test.rb                    |  4 ++++
 5 files changed, 19 insertions(+), 25 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG
index f850ec94..fb396b0d 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,6 +1,7 @@
-0.5.0 - pending
+0.5.0 - 14-02-2019
 
 - Breaking change: listen only to localhost by default to prevent unintended insecure configuration
+- FIX: Avoid calling `hostname` aggressively, instead cache it on the exporter instance
 
 0.4.17 - 13-01-2019
 
diff --git a/lib/prometheus_exporter.rb b/lib/prometheus_exporter.rb
index ea8b6282..ddcf7eb0 100644
--- a/lib/prometheus_exporter.rb
+++ b/lib/prometheus_exporter.rb
@@ -20,6 +20,17 @@ def self.dump(obj)
     end
   end
 
+  def self.hostname
+    @hostname ||=
+      begin
+        require 'socket'
+        Socket.gethostname
+      rescue => e
+        STDERR.puts "Unable to lookup hostname #{e}"
+        "unknown-host"
+      end
+  end
+
   def self.detect_json_serializer(preferred)
     if preferred.nil?
       preferred = :oj if has_oj?
diff --git a/lib/prometheus_exporter/instrumentation/active_record.rb b/lib/prometheus_exporter/instrumentation/active_record.rb
index de59020c..174f9a3a 100644
--- a/lib/prometheus_exporter/instrumentation/active_record.rb
+++ b/lib/prometheus_exporter/instrumentation/active_record.rb
@@ -51,17 +51,6 @@ def self.stop
     def initialize(metric_labels, config_labels)
       @metric_labels = metric_labels
       @config_labels = config_labels
-      @hostname = nil
-    end
-
-    def hostname
-      @hostname ||=
-        begin
-          `hostname`.strip
-        rescue => e
-          STDERR.puts "Unable to lookup hostname #{e}"
-          "unknown-host"
-        end
     end
 
     def collect
@@ -87,7 +76,7 @@ def collect_active_record_pool_stats(metrics)
         metric = {
           pid: pid,
           type: "active_record",
-          hostname: hostname,
+          hostname: ::PrometheusExporter.hostname,
           metric_labels: labels
         }
         metric.merge!(pool.stat)
diff --git a/lib/prometheus_exporter/instrumentation/process.rb b/lib/prometheus_exporter/instrumentation/process.rb
index 3d79002e..bf891e3a 100644
--- a/lib/prometheus_exporter/instrumentation/process.rb
+++ b/lib/prometheus_exporter/instrumentation/process.rb
@@ -42,24 +42,13 @@ def self.stop
 
     def initialize(metric_labels)
       @metric_labels = metric_labels
-      @hostname = nil
-    end
-
-    def hostname
-      @hostname ||=
-        begin
-          `hostname`.strip
-        rescue => e
-          STDERR.puts "Unable to lookup hostname #{e}"
-          "unknown-host"
-        end
     end
 
     def collect
       metric = {}
       metric[:type] = "process"
       metric[:metric_labels] = @metric_labels
-      metric[:hostname] = hostname
+      metric[:hostname] = ::PrometheusExporter.hostname
       collect_gc_stats(metric)
       collect_v8_stats(metric)
       collect_process_stats(metric)
diff --git a/test/prometheus_exporter_test.rb b/test/prometheus_exporter_test.rb
index f1c42a23..7638b5c8 100644
--- a/test/prometheus_exporter_test.rb
+++ b/test/prometheus_exporter_test.rb
@@ -6,4 +6,8 @@ class PrometheusExporterTest < Minitest::Test
   def test_that_it_has_a_version_number
     refute_nil ::PrometheusExporter::VERSION
   end
+
+  def test_it_can_get_hostname
+    assert_equal `hostname`.strip, ::PrometheusExporter.hostname
+  end
 end