Add basic server status page at /status.

Lists versions of various dependencies plus some Postgres and Redis
metrics.

app/controllers/status_controller.rb

@@ -0,0 +1,8 @@
+class StatusController < ApplicationController
+  respond_to :html, :json, :xml
+
+  def show
+    @status = ServerStatus.new
+    respond_with(@status)
+  end
+end

app/logical/server_status.rb

@@ -0,0 +1,109 @@
+class ServerStatus
+  extend Memoist
+  include ActiveModel::Serializers::JSON
+  include ActiveModel::Serializers::Xml
+
+  def serializable_hash(*options)
+    {
+      status: {
+        hostname: hostname,
+        uptime: uptime,
+        loadavg: loadavg,
+        ruby_version: RUBY_VERSION,
+        distro_version: distro_version,
+        kernel_version: kernel_version,
+        libvips_version: libvips_version,
+        ffmpeg_version: ffmpeg_version,
+        mkvmerge_version: mkvmerge_version,
+        redis_version: redis_version,
+        postgres_version: postgres_version,
+      },
+      postgres: {
+        connection_stats: postgres_connection_stats,
+      },
+      redis: {
+        info: redis_info,
+      }
+    }
+  end
+
+  concerning :InfoMethods do
+    def hostname
+      Socket.gethostname
+    end
+
+    def uptime
+      seconds = File.read("/proc/uptime").split[0].to_f
+      "#{seconds.seconds.in_days.round} days"
+    end
+
+    def loadavg
+      File.read("/proc/loadavg").chomp
+    end
+
+    def kernel_version
+      File.read("/proc/version").chomp
+    end
+
+    def distro_version
+      `source /etc/os-release; echo "$NAME $VERSION"`.chomp
+    end
+
+    def libvips_version
+      Vips::LIBRARY_VERSION
+    end
+
+    def ffmpeg_version
+      version = `ffmpeg -version`
+      version[/ffmpeg version ([0-9.]+)/, 1]
+    end
+
+    def mkvmerge_version
+      `mkvmerge --version`.chomp
+    end
+  end
+
+  concerning :RedisMethods do
+    def redis_info
+      return {} if Rails.cache.try(:redis).nil?
+      Rails.cache.redis.info
+    end
+
+    def redis_used_memory
+      redis_info["used_memory_rss_human"]
+    end
+
+    def redis_version
+      redis_info["redis_version"]
+    end
+  end
+
+  concerning :PostgresMethods do
+    def postgres_version
+      ApplicationRecord.connection.select_value("SELECT version()")
+    end
+
+    def postgres_active_connections
+      ApplicationRecord.connection.select_value("SELECT COUNT(*) FROM pg_stat_activity WHERE state = 'active'")
+    end
+
+    def postgres_connection_stats
+      run_query("SELECT pid, state, query_start, state_change, xact_start, backend_start, backend_type FROM pg_stat_activity ORDER BY state, query_start DESC, backend_type")
+    end
+
+    def run_query(query)
+      result = ApplicationRecord.connection.select_all(query)
+      serialize_result(result)
+    end
+
+    def serialize_result(result)
+      result.rows.map do |row|
+        row.each_with_index.map do |col, i|
+          [result.columns[i], col]
+        end.to_h
+      end
+    end
+  end
+
+  memoize :redis_info
+end

app/views/status/show.html.erb

@@ -0,0 +1,32 @@
+<div id="c-status">
+  <div id="a-show" class="fixed-width-container">
+    <h1>Status</h1>
+
+    <details>
+      <summary>
+        Server: <%= @status.hostname %>
+      </summary>
+      <%= render "list", hash: @status.serializable_hash[:status] %>
+    </details>
+
+    <h1>Postgres</h1>
+
+    <details>
+      <summary>
+        <%= pluralize @status.postgres_active_connections, "active connection" %>.
+      </summary>
+
+      <%= render "table", rows: @status.serializable_hash[:postgres][:connection_stats] %>
+    </details>
+
+    <h1>Redis</h1>
+
+    <details>
+      <summary>
+        <%= @status.redis_used_memory %> memory used.
+      </summary>
+
+      <%= render "list", hash: @status.serializable_hash[:redis][:info] %>
+    </details>
+  </div>
+</div>

config/routes.rb

@@ -227,6 +227,7 @@ Rails.application.routes.draw do
     get :sign_out, on: :collection
   end
   resource :source, :only => [:show]
+  resource :status, only: [:show], controller: "status"
   resources :tags do
     collection do
       get :autocomplete

test/functional/status_controller_test.rb

@@ -0,0 +1,20 @@
+require 'test_helper'
+
+class StatusControllerTest < ActionDispatch::IntegrationTest
+  context "The status controller" do
+    should "work for a html response" do
+      get status_path
+      assert_response :success
+    end
+
+    should "work for a json response" do
+      get status_path(format: :json)
+      assert_response :success
+    end
+
+    should "work for an xml response" do
+      get status_path(format: :json)
+      assert_response :success
+    end
+  end
+end