postgres_exporter: Build from source for per-index stats.

This builds prometheus-community/postgres_exporter#843 to track
per-index statistics.

puppet/zulip/manifests/common.pp

@@ -121,6 +121,12 @@ class zulip::common {
       },
     },
 
+    # https://github.com/prometheus-community/postgres_exporter/pull/843
+    'postgres_exporter-src' => {
+      'version' => '4881e566207b1675f8b2ceae9bcd71f61800ccd1',
+      'sha256'  => '1b0aaf32e3834f02e5448fb21c0de114a4e42cc0937300e307899efb8438bf16',
+    },
+
     # https://github.com/ncabatoff/process-exporter/releases
     'process_exporter' => {
       'version' => '0.7.10',

puppet/zulip_ops/manifests/prometheus/postgresql.pp

@@ -3,15 +3,48 @@
 class zulip_ops::prometheus::postgresql {
   include zulip_ops::prometheus::base
   include zulip::supervisor
+  include zulip::golang
 
-  $version = $zulip::common::versions['postgres_exporter']['version']
-  $dir = "/srv/zulip-postgres_exporter-${version}"
-  $bin = "${dir}/postgres_exporter"
+  $version = $zulip::common::versions['postgres_exporter-src']['version']
+  $dir = "/srv/zulip-postgres_exporter-src-${version}"
+  $bin = "/usr/local/bin/postgres_exporter-${version}-go-${zulip::golang::version}"
 
-  zulip::external_dep { 'postgres_exporter':
+  # Binary builds: https://github.com/prometheus-community/postgres_exporter/releases/download/v${version}/postgres_exporter-${version}.linux-${zulip::common::goarch}.tar.gz
+
+  zulip::external_dep { 'postgres_exporter-src':
     version        => $version,
-    url            => "https://github.com/prometheus-community/postgres_exporter/releases/download/v${version}/postgres_exporter-${version}.linux-${zulip::common::goarch}.tar.gz",
-    tarball_prefix => "postgres_exporter-${version}.linux-${zulip::common::goarch}",
+    url            => "https://github.com/Sticksman/postgres_exporter/archive/${version}.tar.gz",
+    tarball_prefix => "postgres_exporter-${version}",
+  }
+
+  exec { 'compile postgres_exporter':
+    command     => "make build && cp ./postgres_exporter ${bin}",
+    cwd         => $dir,
+    # GOCACHE is required; nothing is written to GOPATH, but it is required to be set
+    environment => ['GOCACHE=/tmp/gocache', 'GOPATH=/root/go'],
+    path        => [
+      "${zulip::golang::dir}/bin",
+      '/usr/local/bin',
+      '/usr/bin',
+      '/bin',
+    ],
+    creates     => $bin,
+    require     => [
+      Zulip::External_Dep['golang'],
+      Zulip::External_Dep['postgres_exporter-src'],
+    ]
+  }
+  # This resource exists purely so it doesn't get tidied; it is
+  # created by the 'compile postgres_exporter' step.
+  file { $bin:
+    ensure  => file,
+    require => Exec['compile postgres_exporter'],
+  }
+  tidy { '/usr/local/bin/postgres_exporter-*':
+    path    => '/usr/local/bin',
+    recurse => 1,
+    matches => 'postgres_exporter-*',
+    require => Exec['compile postgres_exporter'],
   }
 
   exec { 'create prometheus postgres user':
@@ -27,7 +60,7 @@ class zulip_ops::prometheus::postgresql {
       Exec['create prometheus postgres user'],
       User[prometheus],
       Package[supervisor],
-      Zulip::External_Dep['postgres_exporter'],
+      File[$bin],
     ],
     owner   => 'root',
     group   => 'root',

puppet/zulip_ops/templates/supervisor/conf.d/prometheus_postgres_exporter.conf.template.erb

@@ -1,5 +1,5 @@
 [program:prometheus_postgres_exporter]
-command=<%= @bin %>
+command=<%= @bin %> --collector.stat_user_indexes
 environment=DATA_SOURCE_NAME="postgresql://prometheus@:5432/zulip?host=/var/run/postgresql"
 priority=10
 autostart=true