Log an activity event when an Agent connects

Changelog: added

app/models/clusters/agent.rb

@@ -4,6 +4,8 @@ module Clusters
   class Agent < ApplicationRecord
     self.table_name = 'cluster_agents'
 
+    INACTIVE_AFTER = 1.hour.freeze
+
     belongs_to :created_by_user, class_name: 'User', optional: true
     belongs_to :project, class_name: '::Project' # Otherwise, it will load ::Clusters::Project
 
@@ -33,5 +35,9 @@ module Clusters
     def has_access_to?(requested_project)
       requested_project == project
     end
+
+    def active?
+      agent_tokens.where("last_used_at > ?", INACTIVE_AFTER.ago).exists?
+    end
   end
 end

app/models/clusters/agent_token.rb

@@ -28,8 +28,12 @@ module Clusters
 
       cache_attributes(track_values)
 
-      # Use update_column so updated_at is skipped
-      update_columns(track_values) if can_update_track_values?
+      if can_update_track_values?
+        log_activity_event!(track_values[:last_used_at]) unless agent.active?
+
+        # Use update_column so updated_at is skipped
+        update_columns(track_values)
+      end
     end
 
     private
@@ -44,5 +48,14 @@ module Clusters
       real_last_used_at.nil? ||
         (Time.current - real_last_used_at) >= last_used_at_max_age
     end
+
+    def log_activity_event!(recorded_at)
+      agent.activity_events.create!(
+        kind: :agent_connected,
+        level: :info,
+        recorded_at: recorded_at,
+        agent_token: self
+      )
+    end
   end
 end

app/models/clusters/agents/activity_event.rb

@@ -18,7 +18,10 @@ module Clusters
       nullify_if_blank :detail
 
       enum kind: {
-        token_created: 0
+        token_created: 0,
+        token_revoked: 1,
+        agent_connected: 2,
+        agent_disconnected: 3
       }, _prefix: true
 
       enum level: {

spec/models/clusters/agent_spec.rb

@@ -75,4 +75,37 @@ RSpec.describe Clusters::Agent do
       expect(agent.has_access_to?(create(:project))).to be_falsey
     end
   end
+
+  describe '#active?' do
+    let_it_be(:agent) { create(:cluster_agent) }
+
+    let!(:token) { create(:cluster_agent_token, agent: agent, last_used_at: last_used_at) }
+
+    subject { agent.active? }
+
+    context 'agent has never connected' do
+      let(:last_used_at) { nil }
+
+      it { is_expected.to be_falsey }
+    end
+
+    context 'agent has connected, but not recently' do
+      let(:last_used_at) { 2.hours.ago }
+
+      it { is_expected.to be_falsey }
+    end
+
+    context 'agent has connected recently' do
+      let(:last_used_at) { 2.minutes.ago }
+
+      it { is_expected.to be_truthy }
+    end
+
+    context 'agent has multiple tokens' do
+      let!(:inactive_token) { create(:cluster_agent_token, agent: agent, last_used_at: 2.hours.ago) }
+      let(:last_used_at) { 2.minutes.ago }
+
+      it { is_expected.to be_truthy }
+    end
+  end
 end

spec/models/clusters/agent_token_spec.rb

@@ -39,7 +39,9 @@ RSpec.describe Clusters::AgentToken do
   end
 
   describe '#track_usage', :clean_gitlab_redis_cache do
-    let(:agent_token) { create(:cluster_agent_token) }
+    let_it_be(:agent) { create(:cluster_agent) }
+
+    let(:agent_token) { create(:cluster_agent_token, agent: agent) }
 
     subject { agent_token.track_usage }
 
@@ -73,6 +75,34 @@ RSpec.describe Clusters::AgentToken do
           expect_redis_update
         end
       end
+
+      context 'agent is inactive' do
+        before do
+          allow(agent).to receive(:active?).and_return(false)
+        end
+
+        it 'creates an activity event' do
+          expect { subject }.to change { agent.activity_events.count }
+
+          event = agent.activity_events.last
+          expect(event).to have_attributes(
+            kind: 'agent_connected',
+            level: 'info',
+            recorded_at: agent_token.reload.read_attribute(:last_used_at),
+            agent_token: agent_token
+          )
+        end
+      end
+
+      context 'agent is active' do
+        before do
+          allow(agent).to receive(:active?).and_return(true)
+        end
+
+        it 'does not create an activity event' do
+          expect { subject }.not_to change { agent.activity_events.count }
+        end
+      end
     end
 
     def expect_redis_update