From 07336b0e146fb451c2f1ebfc11422f48e2d77a7b Mon Sep 17 00:00:00 2001
From: Molham Al Nasr <m.al-nasr@bnotk.de>
Date: Tue, 14 Jan 2025 11:32:32 +0100
Subject: [PATCH 1/2] fix(Containers resolver): properly detect Docker runtime
 in containers (#2781)

Previously, the `Containers` resolver would always return a value from
`read_environ`, preventing `read_cgroup` from being called. As a result,
the `hypervisors` and `virtual` facts were often set incorrectly to
`container_other` and displayed a misleading warning.

Changes in this commit:
- `read_cgroup` now returns early unless Docker or LXC matches are found.
- `read_environ` returns `nil` when encountering an unsupported container.
- If both methods return `nil`, `vm` defaults to `container_other` with a warning.

These updates ensure that Facter correctly detects Docker and properly
reports the `virtual` and `hypervisors` facts when running inside a
Docker container.
---
 lib/facter/resolvers/containers.rb | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/lib/facter/resolvers/containers.rb b/lib/facter/resolvers/containers.rb
index 030d7267a4..7851fc1b87 100644
--- a/lib/facter/resolvers/containers.rb
+++ b/lib/facter/resolvers/containers.rb
@@ -15,7 +15,17 @@ class << self
 
         def post_resolve(fact_name, _options)
           @fact_list.fetch(fact_name) do
-            read_environ(fact_name) || read_cgroup(fact_name)
+            environ_result = read_environ(fact_name)
+            cgroup_result = read_cgroup(fact_name)
+
+            if environ_result.nil? && cgroup_result.nil?
+              @fact_list[:vm] = 'container_other'
+              @fact_list[:hypervisor] = ''
+              log.warn("Container runtime is unsupported, setting to 'container_other'")
+              @fact_list[fact_name]
+            else
+              environ_result || cgroup_result
+            end
           end
         end
 
@@ -24,7 +34,8 @@ def read_cgroup(fact_name)
           return unless output_cgroup
 
           output_docker = %r{docker/(.+)}.match(output_cgroup)
-          output_lxc = %r{^/lxc/([^/]+)}.match(output_cgroup)
+          output_lxc    = %r{^/lxc/([^/]+)}.match(output_cgroup)
+          return if output_docker.nil? && output_lxc.nil?
 
           info, vm = extract_vm_and_info(output_docker, output_lxc)
           @fact_list[:vm] = vm
@@ -57,8 +68,7 @@ def read_environ(fact_name)
             vm = 'systemd_nspawn'
             info = { 'id' => Facter::Util::FileHelper.safe_read('/etc/machine-id', nil).strip }
           else
-            vm = 'container_other'
-            log.warn("Container runtime, '#{container}', is unsupported, setting to '#{vm}'")
+            return nil
           end
           @fact_list[:vm] = vm
           @fact_list[:hypervisor] = { vm.to_sym => info } if vm

From a360b329890de67bcd1ae669af8382b4d779a4e6 Mon Sep 17 00:00:00 2001
From: Molham Al Nasr <m.al-nasr@bnotk.de>
Date: Thu, 13 Feb 2025 13:59:59 +0100
Subject: [PATCH 2/2] fix(Containers resolver): remove dummy value return
 'container_other' to allow VirtualDetector to continue it's checks

---
 lib/facter/resolvers/containers.rb | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/lib/facter/resolvers/containers.rb b/lib/facter/resolvers/containers.rb
index 7851fc1b87..b0acd1ad65 100644
--- a/lib/facter/resolvers/containers.rb
+++ b/lib/facter/resolvers/containers.rb
@@ -1,5 +1,10 @@
 # frozen_string_literal: true
 
+# The Facter::Resolvers::Containers.resolve method must return either a valid container identifier (e.g., "docker", "lxc", etc.)
+# or nil if no container is detected. It should not return a dummy value such as "container_other". This is critical because
+# Facter::Util::Facts::Posix::VirtualDetector relies on a nil return value to continue checking other virtualization methods.
+# Returning a non-nil dummy value would prematurely short-circuit these checks, leading to inaccurate detection results.
+
 module Facter
   module Resolvers
     class Containers < BaseResolver
@@ -15,17 +20,7 @@ class << self
 
         def post_resolve(fact_name, _options)
           @fact_list.fetch(fact_name) do
-            environ_result = read_environ(fact_name)
-            cgroup_result = read_cgroup(fact_name)
-
-            if environ_result.nil? && cgroup_result.nil?
-              @fact_list[:vm] = 'container_other'
-              @fact_list[:hypervisor] = ''
-              log.warn("Container runtime is unsupported, setting to 'container_other'")
-              @fact_list[fact_name]
-            else
-              environ_result || cgroup_result
-            end
+            read_environ(fact_name) || read_cgroup(fact_name)
           end
         end