feat: add opt-in dynamic ILM resolution for sprintf-based alias and policy

lib/logstash/outputs/elasticsearch.rb

@@ -450,6 +450,8 @@ def stop_after_successful_connection_thread
 
   # Convert the event into a 3-tuple of action, params and event hash
   def event_action_tuple(event)
+    ensure_dynamic_ilm_resources!(event) if ilm_in_use? && ilm_has_sprintf?
+
     params = common_event_params(event)
     params[:_type] = get_event_type(event) if use_event_type?(nil)
 
@@ -566,6 +568,12 @@ def resolve_document_id(event, event_id)
   private :resolve_document_id
 
   def resolve_index!(event, event_index)
+    if ilm_in_use? && ilm_has_sprintf?
+      dynamic_alias = resolve_dynamic_ilm_rollover_alias!(event)
+      raise IndexInterpolationError, dynamic_alias if dynamic_alias.match(/%{.*?}/) && dlq_on_failed_indexname_interpolation
+      return dynamic_alias
+    end
+
     sprintf_index = @event_target.call(event)
     raise IndexInterpolationError, sprintf_index if sprintf_index.match(/%{.*?}/) && dlq_on_failed_indexname_interpolation
     # if it's not a data stream, sprintf_index is the @index with resolved placeholders.

lib/logstash/outputs/elasticsearch/ilm.rb

@@ -4,12 +4,55 @@ module Ilm
     ILM_POLICY_PATH = "default-ilm-policy.json"
 
     def setup_ilm
+      return if ilm_has_sprintf?
+
       logger.warn("Overwriting supplied index #{@index} with rollover alias #{@ilm_rollover_alias}") unless default_index?(@index)
       @index = @ilm_rollover_alias
       maybe_create_rollover_alias
       maybe_create_ilm_policy
     end
 
+    def ilm_has_sprintf?
+      (@ilm_rollover_alias && @ilm_rollover_alias.match(/%{.*?}/)) ||
+        (@ilm_policy && @ilm_policy.match(/%{.*?}/))
+    end
+
+    def resolve_dynamic_ilm_rollover_alias!(event)
+      resolve_dynamic_ilm_value!(event, @ilm_rollover_alias, "ilm_rollover_alias")
+    end
+
+    def resolve_dynamic_ilm_policy!(event)
+      resolve_dynamic_ilm_value!(event, @ilm_policy, "ilm_policy")
+    end
+
+    def ensure_dynamic_ilm_resources!(event)
+      return unless ilm_in_use? && ilm_has_sprintf?
+
+      resolved_alias = resolve_dynamic_ilm_rollover_alias!(event)
+      resolved_policy = resolve_dynamic_ilm_policy!(event)
+
+      @dynamic_ilm_validation_lock ||= Mutex.new
+      @dynamic_ilm_validated_keys ||= {}
+      validation_key = "#{resolved_alias}|#{resolved_policy}"
+      return if @dynamic_ilm_validated_keys[validation_key]
+
+      @dynamic_ilm_validation_lock.synchronize do
+        return if @dynamic_ilm_validated_keys[validation_key]
+
+        unless client.ilm_policy_exists?(resolved_policy)
+          raise EventMappingError, "Dynamic ILM policy '#{resolved_policy}' does not exist. " \
+            "Pre-create policy, template, and rollover alias resources before using dynamic ILM."
+        end
+
+        unless client.rollover_alias_exists?(resolved_alias)
+          raise EventMappingError, "Dynamic ILM rollover alias '#{resolved_alias}' does not exist. " \
+            "Pre-create policy, template, and rollover alias resources before using dynamic ILM."
+        end
+
+        @dynamic_ilm_validated_keys[validation_key] = true
+      end
+    end
+
     def ilm_in_use?
       return @ilm_actually_enabled if defined?(@ilm_actually_enabled)
       @ilm_actually_enabled =
@@ -32,6 +75,20 @@ def ilm_in_use?
 
     private
 
+    def resolve_dynamic_ilm_value!(event, pattern, setting_name)
+      resolved = event.sprintf(pattern)
+
+      if resolved.nil? || resolved.empty?
+        raise EventMappingError, "#{setting_name} resolved to empty value from pattern: #{pattern}"
+      end
+
+      if resolved.match(/%{.*?}/)
+        raise EventMappingError, "#{setting_name} contains unresolved placeholders: #{resolved}"
+      end
+
+      resolved
+    end
+
     def ilm_alias_set?
       default_index?(@index) || !default_rollover_alias?(@ilm_rollover_alias)
     end

spec/unit/outputs/elasticsearch_spec.rb

@@ -264,6 +264,58 @@
       end
     end
 
+    describe "dynamic ILM resolution" do
+      let(:options) do
+        super().merge(
+          "ilm_enabled" => true,
+          "ilm_rollover_alias" => "%{[service]}",
+          "ilm_policy" => "%{[service]}-policy"
+        )
+      end
+
+      let(:event) { LogStash::Event.new("service" => "checkout") }
+
+      before do
+        allow(subject).to receive(:ilm_in_use?).and_return(true)
+      end
+
+      it "uses resolved rollover alias as the target index" do
+        allow(subject.client).to receive(:ilm_policy_exists?).with("checkout-policy").and_return(true)
+        allow(subject.client).to receive(:rollover_alias_exists?).with("checkout").and_return(true)
+
+        expect(subject.send(:event_action_tuple, event)[1]).to include(:_index => "checkout")
+      end
+
+      it "validates dynamic policy and alias once per resolved combination" do
+        expect(subject.client).to receive(:ilm_policy_exists?).with("checkout-policy").once.and_return(true)
+        expect(subject.client).to receive(:rollover_alias_exists?).with("checkout").once.and_return(true)
+
+        subject.send(:event_action_tuple, event)
+        subject.send(:event_action_tuple, event)
+      end
+
+      it "raises an event mapping error when policy is missing" do
+        allow(subject.client).to receive(:ilm_policy_exists?).with("checkout-policy").and_return(false)
+
+        expect { subject.send(:event_action_tuple, event) }
+          .to raise_error(LogStash::Outputs::ElasticSearch::EventMappingError, /Dynamic ILM policy 'checkout-policy' does not exist/)
+      end
+
+      it "raises an event mapping error when placeholders are unresolved" do
+        unresolved_event = LogStash::Event.new({})
+
+        expect { subject.send(:event_action_tuple, unresolved_event) }
+          .to raise_error(LogStash::Outputs::ElasticSearch::EventMappingError, /contains unresolved placeholders/)
+      end
+
+      it "skips startup ILM bootstrap in dynamic mode" do
+        expect(subject).not_to receive(:maybe_create_rollover_alias)
+        expect(subject).not_to receive(:maybe_create_ilm_policy)
+
+        subject.send(:setup_ilm)
+      end
+    end
+
     describe "with event integration metadata" do
       let(:event_fields) {{}}
       let(:event) { LogStash::Event.new(event_fields)}