diff --git a/logstash-core/lib/logstash/agent.rb b/logstash-core/lib/logstash/agent.rb
index 32ad2ba8b..0a42eeae9 100644
--- a/logstash-core/lib/logstash/agent.rb
+++ b/logstash-core/lib/logstash/agent.rb
@@ -88,9 +88,9 @@ class LogStash::Agent
   # @param pipeline_id [String] pipeline string identifier
   # @param settings [Hash] settings that will be passed when creating the pipeline.
   #   keys should be symbols such as :pipeline_workers and :pipeline_batch_delay
-  def register_pipeline(pipeline_id, settings = @settings)
+  def register_pipeline(settings)
     pipeline_settings = settings.clone
-    pipeline_settings.set("pipeline.id", pipeline_id)
+    pipeline_id = pipeline_settings.get("pipeline.id")
 
     pipeline = create_pipeline(pipeline_settings)
     return unless pipeline.is_a?(LogStash::Pipeline)
diff --git a/logstash-core/lib/logstash/runner.rb b/logstash-core/lib/logstash/runner.rb
index 78d291829..924d42a8f 100644
--- a/logstash-core/lib/logstash/runner.rb
+++ b/logstash-core/lib/logstash/runner.rb
@@ -261,7 +261,7 @@ class LogStash::Runner < Clamp::StrictCommand
 
     @agent = create_agent(@settings)
 
-    @agent.register_pipeline("main", @settings)
+    @agent.register_pipeline(@settings)
 
     # enable sigint/sigterm before starting the agent
     # to properly handle a stalled agent
diff --git a/logstash-core/spec/api/spec_helper.rb b/logstash-core/spec/api/spec_helper.rb
index bcb37ecfc..a984f13cd 100644
--- a/logstash-core/spec/api/spec_helper.rb
+++ b/logstash-core/spec/api/spec_helper.rb
@@ -59,7 +59,7 @@ class LogStashRunner
   def start
     # We start a pipeline that will generate a finite number of events
     # before starting the expectations
-    agent.register_pipeline("main", @settings)
+    agent.register_pipeline(@settings)
     @agent_task = Stud::Task.new { agent.execute }
     @agent_task.wait
   end
diff --git a/logstash-core/spec/logstash/agent_spec.rb b/logstash-core/spec/logstash/agent_spec.rb
index 699eecd9d..27be48cd7 100644
--- a/logstash-core/spec/logstash/agent_spec.rb
+++ b/logstash-core/spec/logstash/agent_spec.rb
@@ -9,6 +9,7 @@ require_relative "../support/helpers"
 describe LogStash::Agent do
 
   let(:agent_settings) { LogStash::SETTINGS }
+  let(:default_pipeline_id) { LogStash::SETTINGS.get("pipeline.id") }
   let(:agent_args) { {} }
   let(:pipeline_settings) { agent_settings.clone }
   let(:pipeline_args) { {} }
@@ -41,7 +42,6 @@ describe LogStash::Agent do
   end
 
   describe "register_pipeline" do
-    let(:pipeline_id) { "main" }
     let(:config_string) { "input { } filter { } output { }" }
     let(:agent_args) do
       {
@@ -57,7 +57,7 @@ describe LogStash::Agent do
         expect(arg1).to eq(config_string)
         expect(arg2.to_hash).to include(agent_args)
       end
-      subject.register_pipeline(pipeline_id, agent_settings)
+      subject.register_pipeline(agent_settings)
     end
   end
 
@@ -90,10 +90,9 @@ describe LogStash::Agent do
           "path.config" => config_file
         }
       end
-      let(:pipeline_id) { "main" }
 
       before(:each) do
-        subject.register_pipeline(pipeline_id, pipeline_settings)
+        subject.register_pipeline(pipeline_settings)
       end
 
       context "if state is clean" do
@@ -195,10 +194,9 @@ describe LogStash::Agent do
           "path.config" => config_file,
         }
       end
-      let(:pipeline_id) { "main" }
 
       before(:each) do
-        subject.register_pipeline(pipeline_id, pipeline_settings)
+        subject.register_pipeline(pipeline_settings)
       end
 
       context "if state is clean" do
@@ -249,7 +247,6 @@ describe LogStash::Agent do
   end
 
   describe "#reload_state!" do
-    let(:pipeline_id) { "main" }
     let(:first_pipeline_config) { "input { } filter { } output { }" }
     let(:second_pipeline_config) { "input { generator {} } filter { } output { }" }
     let(:pipeline_args) { {
@@ -259,13 +256,13 @@ describe LogStash::Agent do
     } }
 
     before(:each) do
-      subject.register_pipeline(pipeline_id, pipeline_settings)
+      subject.register_pipeline(pipeline_settings)
     end
 
     context "when fetching a new state" do
       it "upgrades the state" do
         expect(subject).to receive(:fetch_config).and_return(second_pipeline_config)
-        expect(subject).to receive(:upgrade_pipeline).with(pipeline_id, kind_of(LogStash::Pipeline))
+        expect(subject).to receive(:upgrade_pipeline).with(default_pipeline_id, kind_of(LogStash::Pipeline))
         subject.reload_state!
       end
     end
@@ -285,7 +282,6 @@ describe LogStash::Agent do
       "config.reload.interval" => 0.01,
       "config.string" => pipeline_config
     } }
-    let(:pipeline_id) { "main" }
 
     context "environment variable templating" do
       before :each do
@@ -299,14 +295,13 @@ describe LogStash::Agent do
 
       it "doesn't upgrade the state" do
         allow(subject).to receive(:fetch_config).and_return(pipeline_config)
-        subject.register_pipeline(pipeline_id, pipeline_settings)
-        expect(subject.pipelines[pipeline_id].inputs.first.message).to eq("foo-bar")
+        subject.register_pipeline(pipeline_settings)
+        expect(subject.pipelines[default_pipeline_id].inputs.first.message).to eq("foo-bar")
       end
     end
   end
 
   describe "#upgrade_pipeline" do
-    let(:pipeline_id) { "main" }
     let(:pipeline_config) { "input { } filter { } output { }" }
     let(:pipeline_args) { {
       "config.string" => pipeline_config,
@@ -315,7 +310,7 @@ describe LogStash::Agent do
     let(:new_pipeline_config) { "input { generator {} } output { }" }
 
     before(:each) do
-      subject.register_pipeline(pipeline_id, pipeline_settings)
+      subject.register_pipeline(pipeline_settings)
     end
 
     after(:each) do
@@ -330,14 +325,14 @@ describe LogStash::Agent do
       end
 
       it "leaves the state untouched" do
-        subject.send(:"reload_pipeline!", pipeline_id)
-        expect(subject.pipelines[pipeline_id].config_str).to eq(pipeline_config)
+        subject.send(:"reload_pipeline!", default_pipeline_id)
+        expect(subject.pipelines[default_pipeline_id].config_str).to eq(pipeline_config)
       end
 
       context "and current state is empty" do
         it "should not start a pipeline" do
           expect(subject).to_not receive(:start_pipeline)
-          subject.send(:"reload_pipeline!", pipeline_id)
+          subject.send(:"reload_pipeline!", default_pipeline_id)
         end
       end
     end
@@ -350,13 +345,13 @@ describe LogStash::Agent do
         allow(subject).to receive(:start_pipeline)
       end
       it "updates the state" do
-        subject.send(:"reload_pipeline!", pipeline_id)
-        expect(subject.pipelines[pipeline_id].config_str).to eq(new_config)
+        subject.send(:"reload_pipeline!", default_pipeline_id)
+        expect(subject.pipelines[default_pipeline_id].config_str).to eq(new_config)
       end
       it "starts the pipeline" do
         expect(subject).to receive(:stop_pipeline)
         expect(subject).to receive(:start_pipeline)
-        subject.send(:"reload_pipeline!", pipeline_id)
+        subject.send(:"reload_pipeline!", default_pipeline_id)
       end
     end
   end
@@ -430,7 +425,7 @@ describe LogStash::Agent do
       Thread.abort_on_exception = true
 
       @t = Thread.new do
-        subject.register_pipeline("main",  pipeline_settings)
+        subject.register_pipeline(pipeline_settings)
         subject.execute
       end