diff --git a/.env b/.env
index 508087ddc5..51aae70321 100644
--- a/.env
+++ b/.env
@@ -1,6 +1,6 @@
+DD_AGENT_HOST=localhost
+DD_TRACE_AGENT_PORT=8126
 TEST_DDAGENT_API_KEY=invalid_key_but_this_is_fine
-TEST_DDAGENT_HOST=localhost
-TEST_DDAGENT_PORT=8126
 TEST_ELASTICSEARCH_HOST=127.0.0.1
 TEST_ELASTICSEARCH_NATIVE_PORT=9300
 TEST_ELASTICSEARCH_REST_PORT=9200
diff --git a/docker-compose.yml b/docker-compose.yml
index 5215531fe8..99a6319533 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -16,8 +16,8 @@ services:
     env_file: ./.env
     environment:
       - BUNDLE_GEMFILE=/app/Gemfile
+      - DD_AGENT_HOST=ddagent
       - TEST_DATADOG_INTEGRATION=1
-      - TEST_DDAGENT_HOST=ddagent
       - TEST_ELASTICSEARCH_HOST=elasticsearch
       - TEST_MEMCACHED_HOST=memcached
       - TEST_MONGODB_HOST=mongodb
@@ -46,8 +46,8 @@ services:
     env_file: ./.env
     environment:
       - BUNDLE_GEMFILE=/app/Gemfile
+      - DD_AGENT_HOST=ddagent
       - TEST_DATADOG_INTEGRATION=1
-      - TEST_DDAGENT_HOST=ddagent
       - TEST_ELASTICSEARCH_HOST=elasticsearch
       - TEST_MEMCACHED_HOST=memcached
       - TEST_MONGODB_HOST=mongodb
@@ -76,8 +76,8 @@ services:
     env_file: ./.env
     environment:
       - BUNDLE_GEMFILE=/app/Gemfile
+      - DD_AGENT_HOST=ddagent
       - TEST_DATADOG_INTEGRATION=1
-      - TEST_DDAGENT_HOST=ddagent
       - TEST_ELASTICSEARCH_HOST=elasticsearch
       - TEST_MEMCACHED_HOST=memcached
       - TEST_MONGODB_HOST=mongodb
@@ -106,8 +106,8 @@ services:
     env_file: ./.env
     environment:
       - BUNDLE_GEMFILE=/app/Gemfile
+      - DD_AGENT_HOST=ddagent
       - TEST_DATADOG_INTEGRATION=1
-      - TEST_DDAGENT_HOST=ddagent
       - TEST_ELASTICSEARCH_HOST=elasticsearch
       - TEST_MEMCACHED_HOST=memcached
       - TEST_MONGODB_HOST=mongodb
@@ -136,8 +136,8 @@ services:
     env_file: ./.env
     environment:
       - BUNDLE_GEMFILE=/app/Gemfile
+      - DD_AGENT_HOST=ddagent
       - TEST_DATADOG_INTEGRATION=1
-      - TEST_DDAGENT_HOST=ddagent
       - TEST_ELASTICSEARCH_HOST=elasticsearch
       - TEST_MEMCACHED_HOST=memcached
       - TEST_MONGODB_HOST=mongodb
@@ -166,8 +166,8 @@ services:
     env_file: ./.env
     environment:
       - BUNDLE_GEMFILE=/app/Gemfile
+      - DD_AGENT_HOST=ddagent
       - TEST_DATADOG_INTEGRATION=1
-      - TEST_DDAGENT_HOST=ddagent
       - TEST_ELASTICSEARCH_HOST=elasticsearch
       - TEST_MEMCACHED_HOST=memcached
       - TEST_MONGODB_HOST=mongodb
@@ -189,7 +189,7 @@ services:
     expose:
       - "8126"
     ports:
-      - "${TEST_DDAGENT_PORT}:8126"
+      - "${DD_TRACE_AGENT_PORT}:8126"
   elasticsearch:
     # Note: ES 5.0 dies with error:
     # max virtual memory areas vm.max_map_count [65530] is too low, increase to at least [262144]
diff --git a/lib/ddtrace/sync_writer.rb b/lib/ddtrace/sync_writer.rb
index 4742b4ac1f..3c489d60e1 100644
--- a/lib/ddtrace/sync_writer.rb
+++ b/lib/ddtrace/sync_writer.rb
@@ -5,7 +5,8 @@ class SyncWriter
 
     def initialize(options = {})
       @transport = options.fetch(:transport) do
-        HTTPTransport.new(Writer::HOSTNAME, Writer::PORT)
+        transport_options = options.fetch(:transport_options, {})
+        HTTPTransport.new(transport_options)
       end
     end
 
diff --git a/lib/ddtrace/transport.rb b/lib/ddtrace/transport.rb
index 56877f0b1f..6b9e49e29d 100644
--- a/lib/ddtrace/transport.rb
+++ b/lib/ddtrace/transport.rb
@@ -13,6 +13,9 @@ class HTTPTransport
     attr_accessor :hostname, :port
     attr_reader :traces_endpoint, :services_endpoint
 
+    DEFAULT_AGENT_HOST = '127.0.0.1'.freeze
+    DEFAULT_TRACE_AGENT_PORT = '8126'.freeze
+
     # seconds before the transport timeout
     TIMEOUT = 1
 
@@ -45,11 +48,11 @@ class HTTPTransport
 
     private_constant :API
 
-    def initialize(hostname, port, options = {})
+    def initialize(options = {})
       api_version = options.fetch(:api_version, V3)
 
-      @hostname = hostname
-      @port = port
+      @hostname = options[:hostname] || ENV['DD_AGENT_HOST'] || DEFAULT_AGENT_HOST
+      @port = options[:port] || ENV['DD_TRACE_AGENT_PORT'] || DEFAULT_TRACE_AGENT_PORT
       @api = API.fetch(api_version)
       @encoder = options[:encoder] || @api[:encoder]
       @response_callback = options[:response_callback]
diff --git a/lib/ddtrace/writer.rb b/lib/ddtrace/writer.rb
index 416752a807..628e08b34e 100644
--- a/lib/ddtrace/writer.rb
+++ b/lib/ddtrace/writer.rb
@@ -7,9 +7,6 @@ module Datadog
   class Writer
     attr_reader :transport, :worker, :priority_sampler
 
-    HOSTNAME = '127.0.0.1'.freeze
-    PORT = '8126'.freeze
-
     def initialize(options = {})
       # writer and transport parameters
       @buff_size = options.fetch(:buffer_size, 100)
@@ -24,7 +21,7 @@ def initialize(options = {})
 
       # transport and buffers
       @transport = options.fetch(:transport) do
-        HTTPTransport.new(HOSTNAME, PORT, transport_options)
+        HTTPTransport.new(transport_options)
       end
 
       @services = {}
diff --git a/spec/ddtrace/contrib/active_record/multi_db_spec.rb b/spec/ddtrace/contrib/active_record/multi_db_spec.rb
index 58ca696422..18dbf955f7 100644
--- a/spec/ddtrace/contrib/active_record/multi_db_spec.rb
+++ b/spec/ddtrace/contrib/active_record/multi_db_spec.rb
@@ -84,7 +84,6 @@ def mysql_connection_string
     Datadog.registry[:active_record].reset_configuration!
 
     Datadog.configure do |c|
-      c.tracer hostname: ENV.fetch('TEST_DDAGENT_HOST', 'localhost')
       c.use :active_record, configuration_options
     end
   end
diff --git a/spec/ddtrace/contrib/active_record/tracer_spec.rb b/spec/ddtrace/contrib/active_record/tracer_spec.rb
index 95b74c8619..8ea9f47995 100644
--- a/spec/ddtrace/contrib/active_record/tracer_spec.rb
+++ b/spec/ddtrace/contrib/active_record/tracer_spec.rb
@@ -15,7 +15,6 @@
     Datadog.configuration[:active_record].reset_options!
 
     Datadog.configure do |c|
-      c.tracer hostname: ENV.fetch('TEST_DDAGENT_HOST', 'localhost')
       c.use :active_record, configuration_options
     end
   end
diff --git a/spec/ddtrace/contrib/rack/middleware_spec.rb b/spec/ddtrace/contrib/rack/middleware_spec.rb
index df2b0afcd0..887083afa4 100644
--- a/spec/ddtrace/contrib/rack/middleware_spec.rb
+++ b/spec/ddtrace/contrib/rack/middleware_spec.rb
@@ -13,7 +13,6 @@
 
   before(:each) do
     Datadog.configure do |c|
-      c.tracer hostname: ENV.fetch('TEST_DDAGENT_HOST', 'localhost')
       c.use :rack, configuration_options
     end
   end
diff --git a/spec/ddtrace/contrib/rails/railtie_spec.rb b/spec/ddtrace/contrib/rails/railtie_spec.rb
index 60914eaf13..7aaa2825d2 100644
--- a/spec/ddtrace/contrib/rails/railtie_spec.rb
+++ b/spec/ddtrace/contrib/rails/railtie_spec.rb
@@ -32,7 +32,6 @@ def index
 
   before(:each) do
     Datadog.configure do |c|
-      c.tracer hostname: ENV.fetch('TEST_DDAGENT_HOST', 'localhost')
       c.use :rails, rails_options if use_rails
     end
   end
diff --git a/spec/ddtrace/contrib/redis/integration_spec.rb b/spec/ddtrace/contrib/redis/integration_spec.rb
index 162a773402..b3bd3e332d 100644
--- a/spec/ddtrace/contrib/redis/integration_spec.rb
+++ b/spec/ddtrace/contrib/redis/integration_spec.rb
@@ -8,9 +8,7 @@
 RSpec.describe 'Redis integration test' do
   # Use real tracer
   let(:tracer) do
-    Datadog::Tracer.new.tap do |tracer|
-      tracer.configure(hostname: ENV.fetch('TEST_DDAGENT_HOST', 'localhost'))
-    end
+    Datadog::Tracer.new
   end
 
   before(:each) do
diff --git a/spec/ddtrace/contrib/redis/method_replaced_spec.rb b/spec/ddtrace/contrib/redis/method_replaced_spec.rb
index 129698489a..9121861db8 100644
--- a/spec/ddtrace/contrib/redis/method_replaced_spec.rb
+++ b/spec/ddtrace/contrib/redis/method_replaced_spec.rb
@@ -9,7 +9,6 @@
     skip unless ENV['TEST_DATADOG_INTEGRATION']
 
     Datadog.configure do |c|
-      c.tracer hostname: ENV.fetch('TEST_DDAGENT_HOST', 'localhost')
       c.use :redis
     end
   end
diff --git a/spec/ddtrace/integration_spec.rb b/spec/ddtrace/integration_spec.rb
index 08c5ba5bc6..901e874126 100644
--- a/spec/ddtrace/integration_spec.rb
+++ b/spec/ddtrace/integration_spec.rb
@@ -11,9 +11,7 @@
     let(:tracer) do
       Datadog::Tracer.new.tap do |t|
         t.configure(
-          enabled: true,
-          hostname: ENV.fetch('TEST_DDAGENT_HOST', 'localhost'),
-          port: ENV.fetch('TEST_DDAGENT_PORT', 8126)
+          enabled: true
         )
       end
     end
@@ -189,8 +187,6 @@ def agent_receives_span_step3(previous_success)
     before(:each) do
       tracer.configure(
         enabled: true,
-        hostname: ENV.fetch('TEST_DDAGENT_HOST', 'localhost'),
-        port: ENV.fetch('TEST_DDAGENT_PORT', 8126),
         priority_sampling: true
       )
     end
diff --git a/spec/ddtrace/transport_spec.rb b/spec/ddtrace/transport_spec.rb
index d2349472fd..c602ee3686 100644
--- a/spec/ddtrace/transport_spec.rb
+++ b/spec/ddtrace/transport_spec.rb
@@ -3,13 +3,7 @@
 require 'ddtrace'
 
 RSpec.describe Datadog::HTTPTransport do
-  let(:transport) do
-    described_class.new(
-      ENV.fetch('TEST_DDAGENT_HOST', 'localhost'),
-      ENV.fetch('TEST_DDAGENT_PORT', 8126),
-      options
-    )
-  end
+  let(:transport) { described_class.new(options) }
   let(:options) { {} }
 
   before(:each) do
@@ -66,7 +60,7 @@
       end
 
       context 'and a bad transport' do
-        let(:transport) { described_class.new('localhost', '8888') }
+        let(:transport) { described_class.new(hostname: 'localhost', port: '8888') }
         it { expect(transport.server_error?(code)).to be true }
       end
 
diff --git a/spec/ddtrace/workers_integration_spec.rb b/spec/ddtrace/workers_integration_spec.rb
index fe563870c3..c2653accbf 100644
--- a/spec/ddtrace/workers_integration_spec.rb
+++ b/spec/ddtrace/workers_integration_spec.rb
@@ -42,7 +42,7 @@
     end
   end
 
-  let(:transport) { SpyTransport.new(hostname, port) }
+  let(:transport) { SpyTransport.new }
 
   def wait_for_flush(num = 1, period = 0.1)
     (20 * flush_interval).to_i.times do
diff --git a/spec/ddtrace/writer_spec.rb b/spec/ddtrace/writer_spec.rb
index 6efafdd7dd..c03b25ba27 100644
--- a/spec/ddtrace/writer_spec.rb
+++ b/spec/ddtrace/writer_spec.rb
@@ -25,9 +25,7 @@
           context 'and default transport options' do
             it do
               sampling_method = described_class.new.method(:sampling_updater)
-              expect(Datadog::HTTPTransport).to receive(:new) do |hostname, port, options|
-                expect(hostname).to eq(described_class::HOSTNAME)
-                expect(port).to eq(described_class::PORT)
+              expect(Datadog::HTTPTransport).to receive(:new) do |options|
                 expect(options).to be_a_kind_of(Hash)
                 expect(options[:api_version]).to eq(Datadog::HTTPTransport::V4)
                 expect(options[:response_callback].source_location).to eq(sampling_method.source_location)
@@ -43,9 +41,7 @@
             let(:response_callback) { double('response callback') }
 
             it do
-              expect(Datadog::HTTPTransport).to receive(:new) do |hostname, port, options|
-                expect(hostname).to eq(described_class::HOSTNAME)
-                expect(port).to eq(described_class::PORT)
+              expect(Datadog::HTTPTransport).to receive(:new) do |options|
                 expect(options).to include(
                   api_version: api_version,
                   response_callback: response_callback
@@ -70,7 +66,9 @@
             let(:callback) { double('callback method') }
 
             let!(:request) { stub_request(:post, endpoint).to_return(response) }
-            let(:endpoint) { "#{Datadog::Writer::HOSTNAME}:#{Datadog::Writer::PORT}/#{api_version}/traces" }
+            let(:hostname) { ENV.fetch('DD_AGENT_HOST', Datadog::HTTPTransport::DEFAULT_AGENT_HOST) }
+            let(:port) { ENV.fetch('DD_TRACE_AGENT_PORT', Datadog::HTTPTransport::DEFAULT_TRACE_AGENT_PORT) }
+            let(:endpoint) { "#{hostname}:#{port}/#{api_version}/traces" }
             let(:response) { { body: body } }
             let(:body) { 'body' }
 
@@ -96,7 +94,7 @@
                 let(:response) { super().merge!(status: 404) }
                 let!(:fallback_request) { stub_request(:post, fallback_endpoint).to_return(body: body) }
                 let(:fallback_endpoint) do
-                  "#{Datadog::Writer::HOSTNAME}:#{Datadog::Writer::PORT}/#{fallback_version}/traces"
+                  "#{hostname}:#{port}/#{fallback_version}/traces"
                 end
                 let(:body) { 'body' }
 
diff --git a/spec/support/faux_writer.rb b/spec/support/faux_writer.rb
index 2b21da7a13..a034603b5a 100644
--- a/spec/support/faux_writer.rb
+++ b/spec/support/faux_writer.rb
@@ -5,7 +5,7 @@
 # FauxWriter is a dummy writer that buffers spans locally.
 class FauxWriter < Datadog::Writer
   def initialize(options = {})
-    options[:transport] ||= FauxTransport.new(HOSTNAME, PORT)
+    options[:transport] ||= FauxTransport.new
     super
     @mutex = Mutex.new
 
diff --git a/spec/support/spy_transport.rb b/spec/support/spy_transport.rb
index 97fa2bdffd..a17b5c7ce5 100644
--- a/spec/support/spy_transport.rb
+++ b/spec/support/spy_transport.rb
@@ -5,8 +5,8 @@
 class SpyTransport < Datadog::HTTPTransport
   attr_reader :helper_sent
 
-  def initialize(hostname, port)
-    super(hostname, port)
+  def initialize(options = {})
+    super
     @helper_sent = { 200 => {}, 500 => {} }
     @helper_mutex = Mutex.new
     @helper_error_mode = false
diff --git a/test/contrib/rack/helpers.rb b/test/contrib/rack/helpers.rb
index 03db3f2764..7d4f67fbff 100644
--- a/test/contrib/rack/helpers.rb
+++ b/test/contrib/rack/helpers.rb
@@ -122,7 +122,6 @@ def setup
     @tracer = get_test_tracer
 
     Datadog.configure do |c|
-      c.tracer hostname: ENV.fetch('TEST_DDAGENT_HOST', 'localhost')
       c.use :http
       c.use :rack, tracer: @tracer
     end
diff --git a/test/contrib/rails/apps/application.rb b/test/contrib/rails/apps/application.rb
index 41a6f3d184..f2800732eb 100644
--- a/test/contrib/rails/apps/application.rb
+++ b/test/contrib/rails/apps/application.rb
@@ -42,7 +42,6 @@ def config.database_configuration
     def test_config
       # Enables the auto-instrumentation for the testing application
       Datadog.configure do |c|
-        c.tracer hostname: ENV.fetch('TEST_DDAGENT_HOST', 'localhost')
         c.use :rails
         c.use :redis
       end
diff --git a/test/contrib/rails/apps/rails3.rb b/test/contrib/rails/apps/rails3.rb
index f659222e28..0fab71ea43 100644
--- a/test/contrib/rails/apps/rails3.rb
+++ b/test/contrib/rails/apps/rails3.rb
@@ -17,7 +17,6 @@ class Rails3 < Rails::Application
 
 # Enables the auto-instrumentation for the testing application
 Datadog.configure do |c|
-  c.tracer hostname: ENV.fetch('TEST_DDAGENT_HOST', 'localhost')
   c.use :rails
   c.use :redis
 end
diff --git a/test/contrib/sinatra/tracer_activerecord_test.rb b/test/contrib/sinatra/tracer_activerecord_test.rb
index ea540fbe43..930887c3b3 100644
--- a/test/contrib/sinatra/tracer_activerecord_test.rb
+++ b/test/contrib/sinatra/tracer_activerecord_test.rb
@@ -47,7 +47,6 @@ def setup
     app.set :datadog_test_conn, conn
 
     Datadog.configure do |c|
-      c.tracer hostname: ENV.fetch('TEST_DDAGENT_HOST', 'localhost')
       c.use :active_record
     end