Merge pull request #243 from Shopify/mkipper/global-circuit-breaker-simple-integer

Force-enable host-based circuits

Author: Michael Kipper

lib/semian.rb

@@ -296,7 +296,19 @@ def require_keys!(required = [], **options)
   end
 end
 
+def hostname
+  v = %w(KUBE_HOSTNAME KUBE_HOST_NAME KUBE_NODENAME KUBE_NODE_NAME NODENAME NODE_NAME HOSTNAME HOST_NAME)
+  var = v.find { |x| ENV.include?(x) }
+  ENV[var] if var
+end
+
+def force_host_circuits?
+  return false unless ENV.include?('SEMIAN_CIRCUIT_BREAKER_FORCE_HOST')
+  ENV['SEMIAN_CIRCUIT_BREAKER_FORCE_HOST'].split(',').include?(hostname)
+end
+
 if Semian.semaphores_enabled?
+  ENV['SEMIAN_CIRCUIT_BREAKER_IMPL'] = 'host' if force_host_circuits?
   require 'semian/semian'
 else
   Semian::MAX_TICKETS = 0

test/semian_test.rb

@@ -91,4 +91,15 @@ def test_disabled_via_semian_wide_env_var
   ensure
     ENV.delete('SEMIAN_DISABLED')
   end
+
+  def test_force_host_circuits
+    refute force_host_circuits?
+    ENV['SEMIAN_CIRCUIT_BREAKER_FORCE_HOST'] = 'machine-1,machine-2,machine-3'
+    refute force_host_circuits?
+    ENV['KUBE_HOSTNAME'] = 'machine-2'
+    assert force_host_circuits?
+  ensure
+    ENV.delete('SEMIAN_CIRCUIT_BREAKER_FORCE_HOST')
+    ENV.delete('KUBE_HOSTNAME')
+  end
 end