fix: add tests for agent re-discovery mechanism

Signed-off-by: Arjun Rajappa <arjun.rajappa@ibm.com>

Author: arjun-rajappa

test/backend/host_agent_lookup_test.rb

@@ -75,4 +75,19 @@ def test_lookup_with_gateway_no_destination
 
     assert_nil client
   end
+
+  def test_lookup_handles_connection_errors
+    # Test that various connection errors result in nil client
+    stub_request(:get, "http://10.10.10.10:42699/")
+      .to_raise(Errno::ECONNREFUSED)
+
+    subject = Instana::Backend::HostAgentLookup.new('10.10.10.10', 42699)
+
+    client = FakeFS.with_fresh do
+      FakeFS::FileSystem.clone('test/support/ecs', '/proc')
+      subject.call
+    end
+
+    assert_nil client
+  end
 end

test/backend/host_agent_reporting_observer_test.rb

@@ -41,6 +41,12 @@ def test_report_fail
       .to_return(status: 200)
     stub_request(:post, "http://10.10.10.10:9292/com.instana.plugin.ruby.0")
       .to_return(status: 500)
+    stub_request(:get, "http://127.0.0.1:42699/")
+      .to_return(status: 200)
+    stub_request(:put, "http://127.0.0.1:42699/com.instana.plugin.ruby.discovery")
+      .to_return(status: 200, body: '{"pid": 0}')
+    stub_request(:head, "http://127.0.0.1:42699/com.instana.plugin.ruby.0")
+      .to_return(status: 200)
 
     client = Instana::Backend::RequestClient.new('10.10.10.10', 9292)
     discovery = Concurrent::Atom.new({'pid' => 0})
@@ -240,6 +246,13 @@ def test_report_traces_error
     stub_request(:post, "http://10.10.10.10:9292/com.instana.plugin.ruby/traces.1234")
       .to_return(status: 500)
 
+    stub_request(:get, "http://127.0.0.1:42699/")
+      .to_return(status: 200)
+    stub_request(:put, "http://127.0.0.1:42699/com.instana.plugin.ruby.discovery")
+      .to_return(status: 200, body: '{"pid": 1234}')
+    stub_request(:head, "http://127.0.0.1:42699/com.instana.plugin.ruby.1234")
+      .to_return(status: 200)
+
     client = Instana::Backend::RequestClient.new('10.10.10.10', 9292)
     discovery = Concurrent::Atom.new({'pid' => 1234})
 

test/backend/host_agent_test.rb

@@ -86,4 +86,55 @@ def test_after_fork
     subject = Instana::Backend::HostAgent.new
     assert subject.respond_to? :after_fork
   end
+
+  def test_announce_retries_on_connection_failure
+    agent_host = '10.10.10.10'
+    ::Instana.config[:agent_host] = agent_host
+
+    # Simulate connection failures followed by success
+    stub_request(:get, "http://#{agent_host}:42699/")
+      .to_raise(Errno::ECONNREFUSED).times(3).then
+      .to_return(status: 200, body: "", headers: {})
+
+    discovery = Minitest::Mock.new
+    discovery.expect(:delete_observers, discovery, [])
+    discovery.expect(:observers, discovery, [])
+    discovery.expect(:notify_and_delete_observers, discovery, [Object, nil, nil])
+    discovery.expect(:with_observer, discovery, [Instana::Backend::HostAgentActivationObserver])
+    discovery.expect(:with_observer, discovery, [Instana::Backend::HostAgentReportingObserver])
+    discovery.expect(:swap, discovery, [])
+
+    subject = Instana::Backend::HostAgent.new(discovery: discovery)
+
+    FakeFS.with_fresh do
+      FakeFS::FileSystem.clone('test/support/ecs', '/proc')
+      client = subject.announce
+      assert client
+      assert_instance_of Instana::Backend::RequestClient, client
+    end
+
+    discovery.verify
+  ensure
+    ::Instana.config[:agent_host] = '127.0.0.1'
+  end
+
+  def test_announce_returns_nil_after_max_retries
+    agent_host = '10.10.10.10'
+    ::Instana.config[:agent_host] = agent_host
+
+    # Simulate persistent connection failures
+    stub_request(:get, "http://#{agent_host}:42699/")
+      .to_raise(Errno::ECONNREFUSED).times(15)
+
+    discovery = Concurrent::Atom.new(nil)
+    subject = Instana::Backend::HostAgent.new(discovery: discovery)
+
+    FakeFS.with_fresh do
+      FakeFS::FileSystem.clone('test/support/ecs', '/proc')
+      client = subject.announce
+      assert_nil client
+    end
+  ensure
+    ::Instana.config[:agent_host] = '127.0.0.1'
+  end
 end

test/backend/request_client_test.rb

@@ -36,4 +36,48 @@ def test_send_request_failure
 
     refute response.ok?
   end
+
+  def test_connection_errors_return_error_responses
+    subject = Instana::Backend::RequestClient.new('example.com', 9292)
+
+    # Test ECONNREFUSED
+    stub_request(:get, 'http://example.com:9292/refused')
+      .to_raise(Errno::ECONNREFUSED)
+    response = subject.send_request('GET', '/refused')
+    refute response.ok?
+    assert_equal '503', response.code
+    assert_includes response.body, 'Connection refused'
+
+    # Test EHOSTUNREACH
+    stub_request(:get, 'http://example.com:9292/unreachable')
+      .to_raise(Errno::EHOSTUNREACH)
+    response = subject.send_request('GET', '/unreachable')
+    refute response.ok?
+    assert_equal '503', response.code
+    assert_includes response.body, 'Host unreachable'
+
+    # Test Timeout
+    stub_request(:get, 'http://example.com:9292/timeout')
+      .to_timeout
+    response = subject.send_request('GET', '/timeout')
+    refute response.ok?
+    assert_equal '408', response.code
+    assert_includes response.body, 'Timeout'
+
+    # Test SocketError
+    stub_request(:get, 'http://example.com:9292/socket')
+      .to_raise(SocketError.new('Name or service not known'))
+    response = subject.send_request('GET', '/socket')
+    refute response.ok?
+    assert_equal '502', response.code
+    assert_includes response.body, 'Socket error'
+
+    # Test StandardError
+    stub_request(:get, 'http://example.com:9292/error')
+      .to_raise(StandardError.new('Unexpected error'))
+    response = subject.send_request('GET', '/error')
+    refute response.ok?
+    assert_equal '500', response.code
+    assert_includes response.body, 'StandardError'
+  end
 end