diff --git a/README.md b/README.md
index 1923b31d..77722ab0 100644
--- a/README.md
+++ b/README.md
@@ -44,9 +44,9 @@ It is **required** to configure:
 
 Please substitute the example `'https://unleash.herokuapp.com/api'` for the url of your own instance.
 
-### instance_id
+It is **highly recommended** to configure:
+- `instance_id` parameter with a unique identifier for the running instance.
 
-As of version 5.0.3, `instance_id` is now an automatically generated read-only property.
 
 ```ruby
 Unleash.configure do |config|
@@ -84,6 +84,7 @@ Argument | Description | Required? |  Type |  Default Value|
 ---------|-------------|-----------|-------|---------------|
 `url`      | Unleash server URL. | Y | String | N/A |
 `app_name` | Name of your program. | Y | String | N/A |
+`instance_id` | Identifier for the running instance of program. Important so you can trace back to where metrics are being collected from. **Highly recommended be be set.** | N | String | random UUID |
 `environment` | Unleash context option. Could be for example `prod` or `dev`. Not yet in use. **Not** the same as the SDK's [Unleash environment](https://docs.getunleash.io/reference/environments). | N | String | `default` |
 `project_name` | Name of the project to retrieve features from. If not set, all feature flags will be retrieved. | N | String | nil |
 `refresh_interval` | How often the unleash client should check with the server for configuration changes. | N | Integer |  15 |
@@ -141,6 +142,7 @@ Put in `config/initializers/unleash.rb`:
 Unleash.configure do |config|
   config.app_name = Rails.application.class.parent.to_s
   config.url      = 'https://unleash.herokuapp.com/api'
+  # config.instance_id = "#{Socket.gethostname}"
   config.logger   = Rails.logger
 end
 
@@ -149,6 +151,10 @@ UNLEASH = Unleash::Client.new
 # Or if preferred:
 # Rails.configuration.unleash = Unleash::Client.new
 ```
+For `config.instance_id` use a string with a unique identification for the running instance.
+For example: it could be the hostname, if you only run one App per host.
+Or the docker container id, if you are running in docker.
+If it is not set the client will generate an unique UUID for each execution.
 
 To have it available in the `rails console` command as well, also add to the file above:
 ```ruby
@@ -242,6 +248,7 @@ PhusionPassenger.on_event(:starting_worker_process) do |forked|
   if forked
     Unleash.configure do |config|
       config.app_name    = Rails.application.class.parent.to_s
+      # config.instance_id = "#{Socket.gethostname}"
       config.logger      = Rails.logger
       config.url                 = 'https://unleash.herokuapp.com/api'
       config.custom_http_headers = {'Authorization': '<API token>'}
diff --git a/examples/bootstrap.rb b/examples/bootstrap.rb
index 5a775b15..b72c94dc 100755
--- a/examples/bootstrap.rb
+++ b/examples/bootstrap.rb
@@ -10,6 +10,7 @@
   url: 'https://unleash.herokuapp.com/api',
   custom_http_headers: { 'Authorization': '943ca9171e2c884c545c5d82417a655fb77cec970cc3b78a8ff87f4406b495d0' },
   app_name: 'bootstrap-test',
+  instance_id: 'local-test-cli',
   refresh_interval: 2,
   disable_client: true,
   disable_metrics: true,
diff --git a/examples/simple.rb b/examples/simple.rb
index f8995f61..4d74d0d6 100755
--- a/examples/simple.rb
+++ b/examples/simple.rb
@@ -21,6 +21,7 @@
   url: 'https://unleash.herokuapp.com/api',
   custom_http_headers: { 'Authorization': '943ca9171e2c884c545c5d82417a655fb77cec970cc3b78a8ff87f4406b495d0' },
   app_name: 'simple-test',
+  instance_id: 'local-test-cli',
   refresh_interval: 2,
   metrics_interval: 2,
   retry_limit: 2
diff --git a/lib/unleash/configuration.rb b/lib/unleash/configuration.rb
index d1afdec9..fb3dd382 100644
--- a/lib/unleash/configuration.rb
+++ b/lib/unleash/configuration.rb
@@ -8,6 +8,7 @@ class Configuration
       :url,
       :app_name,
       :environment,
+      :instance_id,
       :project_name,
       :custom_http_headers,
       :disable_client,
@@ -22,15 +23,10 @@ class Configuration
       :bootstrap_config,
       :strategies
 
-    attr_reader \
-      :instance_id
-
     def initialize(opts = {})
       validate_custom_http_headers!(opts[:custom_http_headers]) if opts.has_key?(:custom_http_headers)
       set_defaults
 
-      @instance_id = SecureRandom.uuid
-
       initialize_default_logger if opts[:logger].nil?
 
       merge(opts)
@@ -90,6 +86,7 @@ def set_defaults
       self.app_name         = nil
       self.environment      = 'default'
       self.url              = nil
+      self.instance_id      = SecureRandom.uuid
       self.project_name     = nil
       self.disable_client   = false
       self.disable_metrics  = false
diff --git a/spec/unleash/bootstrap/handler_spec.rb b/spec/unleash/bootstrap/handler_spec.rb
index 01d691da..4e31d184 100644
--- a/spec/unleash/bootstrap/handler_spec.rb
+++ b/spec/unleash/bootstrap/handler_spec.rb
@@ -5,6 +5,7 @@
   Unleash.configure do |config|
     config.url      = 'http://unleash-url/'
     config.app_name = 'my-test-app'
+    config.instance_id = 'rspec/test'
     config.custom_http_headers = { 'X-API-KEY' => '123' }
   end
 
diff --git a/spec/unleash/client_spec.rb b/spec/unleash/client_spec.rb
index 9b9c074e..814efbe1 100644
--- a/spec/unleash/client_spec.rb
+++ b/spec/unleash/client_spec.rb
@@ -45,6 +45,7 @@
           'Accept-Encoding' => 'gzip;q=1.0,deflate;q=0.6,identity;q=0.3',
           'Content-Type' => 'application/json',
           'Unleash-Appname' => 'my-test-app',
+          'Unleash-Instanceid' => 'rspec/test',
           'User-Agent' => "UnleashClientRuby/#{Unleash::VERSION} #{RUBY_ENGINE}/#{RUBY_VERSION} [#{RUBY_PLATFORM}]",
           'X-Api-Key' => '123'
         }
@@ -54,12 +55,14 @@
     Unleash.configure do |config|
       config.url      = 'http://test-url/'
       config.app_name = 'my-test-app'
+      config.instance_id = 'rspec/test'
       config.custom_http_headers = { 'X-API-KEY' => '123' }
     end
 
     unleash_client = Unleash::Client.new(
       url: 'http://test-url/',
       app_name: 'my-test-app',
+      instance_id: 'rspec/test',
       custom_http_headers: { 'X-API-KEY' => '123' }
     )
 
@@ -70,14 +73,14 @@
       .with(headers: { 'Content-Type': 'application/json' })
       .with(headers: { 'X-API-KEY': '123', 'Content-Type': 'application/json' })
       .with(headers: { 'UNLEASH-APPNAME': 'my-test-app' })
-      .with(headers: { 'UNLEASH-INSTANCEID': Unleash.configuration.instance_id })
+      .with(headers: { 'UNLEASH-INSTANCEID': 'rspec/test' })
     ).to have_been_made.once
 
     expect(
       a_request(:get, "http://test-url/client/features")
       .with(headers: { 'X-API-KEY': '123' })
       .with(headers: { 'UNLEASH-APPNAME': 'my-test-app' })
-      .with(headers: { 'UNLEASH-INSTANCEID': Unleash.configuration.instance_id })
+      .with(headers: { 'UNLEASH-INSTANCEID': 'rspec/test' })
     ).to have_been_made.once
 
     # Test now sending of metrics
@@ -88,7 +91,7 @@
         .with(headers: { 'Content-Type': 'application/json' })
         .with(headers: { 'X-API-KEY': '123', 'Content-Type': 'application/json' })
         .with(headers: { 'UNLEASH-APPNAME': 'my-test-app' })
-        .with(headers: { 'UNLEASH-INSTANCEID': Unleash.configuration.instance_id })
+        .with(headers: { 'UNLEASH-INSTANCEID': 'rspec/test' })
     ).not_to have_been_made
 
     # Sending metrics, if they have been evaluated:
@@ -100,7 +103,7 @@
       .with(headers: { 'Content-Type': 'application/json' })
       .with(headers: { 'X-API-KEY': '123', 'Content-Type': 'application/json' })
       .with(headers: { 'UNLEASH-APPNAME': 'my-test-app' })
-      .with(headers: { 'UNLEASH-INSTANCEID': Unleash.configuration.instance_id })
+      .with(headers: { 'UNLEASH-INSTANCEID': 'rspec/test' })
       .with{ |request| JSON.parse(request.body)['bucket']['toggles']['Feature.A']['yes'] == 2 }
     ).to have_been_made.once
   end
@@ -113,7 +116,7 @@
           'Content-Type' => 'application/json',
           'Accept-Encoding' => 'gzip;q=1.0,deflate;q=0.6,identity;q=0.3',
           'Unleash-Appname' => 'my-test-app',
-          'Unleash-Instanceid' => Unleash.configuration.instance_id,
+          'Unleash-Instanceid' => 'rspec/test',
           'User-Agent' => "UnleashClientRuby/#{Unleash::VERSION} #{RUBY_ENGINE}/#{RUBY_VERSION} [#{RUBY_PLATFORM}]",
           'X-Api-Key' => '123'
         }
@@ -154,7 +157,7 @@
           'Content-Type' => 'application/json',
           'Accept-Encoding' => 'gzip;q=1.0,deflate;q=0.6,identity;q=0.3',
           'Unleash-Appname' => 'my-test-app',
-          'Unleash-Instanceid' => Unleash.configuration.instance_id,
+          'Unleash-Instanceid' => 'rspec/test',
           'User-Agent' => "UnleashClientRuby/#{Unleash::VERSION} #{RUBY_ENGINE}/#{RUBY_VERSION} [#{RUBY_PLATFORM}]",
           'X-Api-Key' => '123'
         }
@@ -164,6 +167,7 @@
     Unleash.configure do |config|
       config.url      = 'http://test-url/'
       config.app_name = 'my-test-app'
+      config.instance_id = 'rspec/test'
       config.disable_metrics = true
       config.custom_http_headers = { 'X-API-KEY' => '123' }
       config.log_level = Logger::DEBUG
@@ -212,6 +216,7 @@
     Unleash.configure do |config|
       config.url      = 'http://test-url/'
       config.app_name = 'my-test-app'
+      config.instance_id = 'rspec/test'
       config.disable_client = true
       config.disable_metrics = true
       config.custom_http_headers = { 'X-API-KEY' => '123' }
@@ -264,7 +269,7 @@
           'Accept-Encoding' => 'gzip;q=1.0,deflate;q=0.6,identity;q=0.3',
           'Content-Type' => 'application/json',
           'Unleash-Appname' => 'my-test-app',
-          'Unleash-Instanceid' => Unleash.configuration.instance_id,
+          'Unleash-Instanceid' => 'rspec/test',
           'User-Agent' => "UnleashClientRuby/#{Unleash::VERSION} #{RUBY_ENGINE}/#{RUBY_VERSION} [#{RUBY_PLATFORM}]",
           'X-Api-Key' => '123'
         }
@@ -274,6 +279,7 @@
     Unleash.configure do |config|
       config.url      = 'http://test-url/'
       config.app_name = 'my-test-app'
+      config.instance_id = 'rspec/test'
       config.disable_client = false
       config.disable_metrics = true
       config.custom_http_headers = { 'X-API-KEY' => '123' }
@@ -321,7 +327,7 @@
           'Accept-Encoding' => 'gzip;q=1.0,deflate;q=0.6,identity;q=0.3',
           'Content-Type' => 'application/json',
           'Unleash-Appname' => 'my-test-app',
-          'Unleash-Instanceid' => Unleash.configuration.instance_id,
+          'Unleash-Instanceid' => 'rspec/test',
           'User-Agent' => "UnleashClientRuby/#{Unleash::VERSION} #{RUBY_ENGINE}/#{RUBY_VERSION} [#{RUBY_PLATFORM}]",
           'X-Api-Key' => '123'
         }
@@ -331,6 +337,7 @@
     Unleash.configure do |config|
       config.url      = 'http://test-url/'
       config.app_name = 'my-test-app'
+      config.instance_id = 'rspec/test'
       config.disable_client = false
       config.disable_metrics = true
       config.custom_http_headers = { 'X-API-KEY' => '123' }
@@ -350,6 +357,7 @@
     Unleash.configure do |config|
       config.url      = 'http://test-url/'
       config.app_name = 'my-test-app'
+      config.instance_id = 'rspec/test'
       config.disable_client = true
       config.disable_metrics = false
       config.custom_http_headers = { 'X-API-KEY' => '123' }
@@ -597,7 +605,7 @@
             'Accept-Encoding' => 'gzip;q=1.0,deflate;q=0.6,identity;q=0.3',
             'Content-Type' => 'application/json',
             'Unleash-Appname' => 'my-test-app',
-            'Unleash-Instanceid' => Unleash.configuration.instance_id,
+            'Unleash-Instanceid' => 'rspec/test',
             'User-Agent' => "UnleashClientRuby/#{Unleash::VERSION} #{RUBY_ENGINE}/#{RUBY_VERSION} [#{RUBY_PLATFORM}]",
             'X-Api-Key' => '123'
           }
@@ -611,7 +619,7 @@
             'Accept-Encoding' => 'gzip;q=1.0,deflate;q=0.6,identity;q=0.3',
             'Content-Type' => 'application/json',
             'Unleash-Appname' => 'my-test-app',
-            'Unleash-Instanceid' => Unleash.configuration.instance_id,
+            'Unleash-Instanceid' => 'rspec/test',
             'User-Agent' => "UnleashClientRuby/#{Unleash::VERSION} #{RUBY_ENGINE}/#{RUBY_VERSION} [#{RUBY_PLATFORM}]",
             'X-Api-Key' => '123'
           }
diff --git a/spec/unleash/metrics_reporter_spec.rb b/spec/unleash/metrics_reporter_spec.rb
index 2fb95cf2..b8aed969 100644
--- a/spec/unleash/metrics_reporter_spec.rb
+++ b/spec/unleash/metrics_reporter_spec.rb
@@ -13,6 +13,7 @@
 
     Unleash.configuration.url         = 'http://test-url/'
     Unleash.configuration.app_name    = 'my-test-app'
+    Unleash.configuration.instance_id = 'rspec/test'
 
     # Do not test the scheduled calls from client/metrics:
     Unleash.configuration.disable_client = true
@@ -23,6 +24,7 @@
     Unleash.configure do |config|
       config.url      = 'http://test-url/'
       config.app_name = 'my-test-app'
+      config.instance_id = 'rspec/test'
       config.disable_client = true
     end
     Unleash.toggle_metrics = Unleash::Metrics.new
@@ -66,7 +68,7 @@
           'Accept-Encoding' => 'gzip;q=1.0,deflate;q=0.6,identity;q=0.3',
           'Content-Type' => 'application/json',
           'Unleash-Appname' => 'my-test-app',
-          'Unleash-Instanceid' => Unleash.configuration.instance_id,
+          'Unleash-Instanceid' => 'rspec/test',
           'User-Agent' => "UnleashClientRuby/#{Unleash::VERSION} #{RUBY_ENGINE}/#{RUBY_VERSION} [#{RUBY_PLATFORM}]"
         }
       )
@@ -97,7 +99,7 @@
       .with(
         body: hash_including(
           appName: "my-test-app",
-          instanceId: Unleash.configuration.instance_id
+          instanceId: "rspec/test"
         )
       )
   end
diff --git a/spec/unleash/scheduled_executor_spec.rb b/spec/unleash/scheduled_executor_spec.rb
index b11828f7..4337581f 100644
--- a/spec/unleash/scheduled_executor_spec.rb
+++ b/spec/unleash/scheduled_executor_spec.rb
@@ -35,18 +35,18 @@
     max_exceptions = 1
 
     scheduled_executor = Unleash::ScheduledExecutor.new('TesterLoop', 0, max_exceptions)
-    new_app_name = SecureRandom.uuid
-    original_app_name = Unleash.configuration.app_name
+    new_instance_id = SecureRandom.uuid
+    original_instance_id = Unleash.configuration.instance_id
 
     scheduled_executor.run do
-      Unleash.configuration.app_name = new_app_name
+      Unleash.configuration.instance_id = new_instance_id
       raise StopIteration
     end
 
     scheduled_executor.thread.join
-    expect(Unleash.configuration.app_name).to eq(new_app_name)
+    expect(Unleash.configuration.instance_id).to eq(new_instance_id)
 
-    Unleash.configuration.app_name = original_app_name
+    Unleash.configuration.instance_id = original_instance_id
   end
 
   # These two tests are super flaky because they're checking if threading works
@@ -55,39 +55,39 @@
     max_exceptions = 1
 
     scheduled_executor = Unleash::ScheduledExecutor.new('TesterLoop', 0.02, max_exceptions, true)
-    new_app_name = SecureRandom.uuid
-    original_app_name = Unleash.configuration.app_name
+    new_instance_id = SecureRandom.uuid
+    original_instance_id = Unleash.configuration.instance_id
 
     scheduled_executor.run do
-      Unleash.configuration.app_name = new_app_name
+      Unleash.configuration.instance_id = new_instance_id
       raise StopIteration
     end
 
     sleep 0.01
 
-    expect(Unleash.configuration.app_name).to eq(new_app_name)
+    expect(Unleash.configuration.instance_id).to eq(new_instance_id)
     scheduled_executor.thread.join
 
-    Unleash.configuration.app_name = original_app_name
+    Unleash.configuration.instance_id = original_instance_id
   end
 
   xit "will not trigger immediate exection when not set" do
     max_exceptions = 1
 
     scheduled_executor = Unleash::ScheduledExecutor.new('TesterLoop', 0.02, max_exceptions, false)
-    new_app_name = SecureRandom.uuid
-    original_app_name = Unleash.configuration.app_name
+    new_instance_id = SecureRandom.uuid
+    original_instance_id = Unleash.configuration.instance_id
 
     scheduled_executor.run do
-      Unleash.configuration.app_name = new_app_name
+      Unleash.configuration.instance_id = new_instance_id
       raise StopIteration
     end
 
     sleep 0.01
 
-    expect(Unleash.configuration.app_name).to eq(original_app_name)
+    expect(Unleash.configuration.instance_id).to eq(original_instance_id)
     scheduled_executor.thread.join
 
-    Unleash.configuration.app_name = original_app_name
+    Unleash.configuration.instance_id = original_instance_id
   end
 end