Support cgroups v1 and v2 for Docker containers

CHANGELOG.md

@@ -1,5 +1,13 @@
 # New Relic Ruby Agent Release Notes
 
+## dev
+
+Version <dev> brings support for gleaning a Docker container id from cgroups v2 based containers.
+
+- **Feature: Enhance Docker container id reporting**
+
+  Previously, the agent was only capable of determining a host Docker container's ID if the container was based on cgroups v1. Now, containers based on cgroups v2 will also have their container IDs reported to New Relic. [PR#2229](https://github.com/newrelic/newrelic-ruby-agent/issues/2229).
+
 ## v9.5.0
 
 Version 9.5.0 introduces Stripe instrumentation, allows the agent to record additional response information on a transaction when middleware instrumentation is disabled, introduces new `:'sidekiq.args.include'` and `:'sidekiq.args.exclude:` configuration options to permit capturing only certain Sidekiq job arguments, updates Elasticsearch datastore instance metrics, and fixes a bug in `NewRelic::Rack::AgentHooks.needed?`.

lib/new_relic/agent/system_info.rb

@@ -172,15 +172,39 @@ def self.os_version
         proc_try_read('/proc/version')
       end
 
+      # When operating within a Docker container, attempt to obtain the
+      # container id.
+      #
+      # First look for `/proc/self/mountinfo` to exist on disk to signify
+      # cgroups v2. If that file exists, read it and expect it to contain one
+      # or more "/docker/containers/<container_id>/" lines from which the
+      # container id can be gleaned.
+      #
+      # Next look for `/proc/self/cgroup` to exist on disk to signify cgroup v1.
+      # If that file exists, read it and parse the "cpu" group info in the hope
+      # of finding a 64 character container id value.
+      #
+      # For non-cgroups based containers, use a `nil` value for the container
+      # id without generating any warnings or errors.
       def self.docker_container_id
         return unless ruby_os_identifier.include?('linux')
 
+        cgroupsv2_based_id = docker_container_id_for_cgroupsv2
+        return cgroupsv2_based_id if cgroupsv2_based_id
+
         cgroup_info = proc_try_read('/proc/self/cgroup')
         return unless cgroup_info
 
         parse_docker_container_id(cgroup_info)
       end
 
+      def self.docker_container_id_for_cgroupsv2
+        mountinfo = proc_try_read('/proc/self/mountinfo')
+        return unless mountinfo
+
+        Regexp.last_match(1) if mountinfo =~ %r{/docker/containers/([^/]+)/}
+      end
+
       def self.parse_docker_container_id(cgroup_info)
         cpu_cgroup = parse_cgroup_ids(cgroup_info)['cpu']
         return unless cpu_cgroup

test/new_relic/agent/system_info_test.rb

@@ -60,6 +60,7 @@ def setup
     end
   end
 
+  # BEGIN cgroups v1
   container_id_test_dir = File.join(cross_agent_tests_dir, 'docker_container_id')
   container_id_test_cases = load_cross_agent_test(File.join('docker_container_id', 'cases'))
 
@@ -86,6 +87,21 @@ def setup
       end
     end
   end
+  # END cgroups v1
+
+  # BEGIN cgroups v2
+  def test_docker_container_id_is_gleaned_from_mountinfo_for_cgroups_v2
+    skip_unless_minitest5_or_above
+
+    container_id = "And Autumn leaves lie thick and still o'er land that is lost now"
+    mountinfo = "line1\nline2\n/docker/containers/#{container_id}/other/content\nline4\nline5"
+    NewRelic::Agent::SystemInfo.stub :ruby_os_identifier, 'linux' do
+      NewRelic::Agent::SystemInfo.stub :proc_try_read, mountinfo, %w[/proc/self/mountinfo] do
+        assert_equal container_id, NewRelic::Agent::SystemInfo.docker_container_id
+      end
+    end
+  end
+  # END cgroups v2
 
   each_cross_agent_test :dir => 'proc_meminfo', :pattern => '*.txt' do |file|
     if File.basename(file) =~ /^meminfo_(\d+)MB.txt$/
@@ -297,6 +313,7 @@ def test_system_info_bsd_predicate
   def test_supportability_metric_recorded_when_docker_id_unavailable
     NewRelic::Agent::SystemInfo.stubs(:ruby_os_identifier).returns('linux')
     cgroup_info = File.read(File.join(cross_agent_tests_dir, 'docker_container_id', 'invalid-length.txt'))
+    NewRelic::Agent::SystemInfo.expects(:proc_try_read).with('/proc/self/mountinfo').returns(cgroup_info)
     NewRelic::Agent::SystemInfo.expects(:proc_try_read).with('/proc/self/cgroup').returns(cgroup_info)
 
     in_transaction('txn') do