diff --git a/README.md b/README.md
index 82476e1..3aa824d 100644
--- a/README.md
+++ b/README.md
@@ -193,6 +193,54 @@ will result in lookups through the following paths in vault:
     secret/common
 
 
+## Flagged usage - optional
+By default all hiera lookups are done through all backends.
+In case of vault, it might be desirable to skip vault in normal
+hiera lookups, while you already know up front that the key is not present
+in vault.
+Lookups in vault are relatively expensive, since for each key a connection to vault
+is made as many times as there are mounts and even a multiple of that when using the
+`:hierarchy` list.
+Additionally it might also be desirable to lookup keys in vault only.
+
+To accomplish this, the vault backend can be configured with the following:
+
+    :vault:
+        :override_behavior: 'flag'
+        :flag_default: 'vault_only'
+
+To make this work, this gem comes with three specific functions named `hiera_vault`,
+`hiera_vault_array`, and `hiera_vault_hash`, which should be used instead of the
+corresponding normal hiera lookup functions, to get data out of vault.
+Without the `:flag_default` option, or when set to 'vault_first', lookups will be done in vault first, and then in
+the other backends. If `:flag_default` is set to 'vault_only', the `hiera_vault*` functions
+will only use the vault backend.
+With `:override_behavior` set to 'flag', the vault backend will skip looking in vault when
+lookups are done with the normal hiera lookup functions.
+
+When using any of the specific functions, a puppet run will fail with an error stating:
+
+    [hiera-vault] Cannot skip, because vault is unavailable and vault must be read, while override_behavior is 'flag'
+
+
+### Auto-generating and writing secrets with `hiera_vault()` - `:default_field` required
+This works only when `:default_field` has been configured and `:override_behavior: 'flag'` is in
+effect.
+
+When using the following call with `hiera_vault` in your puppet code, a password will be generated
+automatically and stored at the `override` or highest level hierarchy path, in case no `override`
+has been specified:
+
+    $some_password = hiera_vault('some_key', {'generate' => 20}, 'some_override_path')
+
+In case the `key` does not exist at any path in the mounts/hierarchy lists, a password string will
+be generated with the given length, using alphanumeric characters only. Then it will be stored in
+vault at the first path that was examined. As such it is highly recommended to use an override path
+to ensure using the same value on different nodes, in case that's desired.
+In some cases it might be desired to have a different password on each node. In such a case,
+`$::fqdn` can be used as the override parameter.
+
+
 ## SSL
 
 SSL can be configured with the following config variables:
diff --git a/lib/hiera/backend/vault_backend.rb b/lib/hiera/backend/vault_backend.rb
index 902c371..ff1c9f0 100644
--- a/lib/hiera/backend/vault_backend.rb
+++ b/lib/hiera/backend/vault_backend.rb
@@ -6,12 +6,45 @@ class Vault_backend
       def initialize()
         require 'json'
         require 'vault'
+        Hiera.debug("Hiera VAULT backend starting")
 
         @config = Config[:vault]
         @config[:mounts] ||= {}
         @config[:mounts][:generic] ||= ['secret']
         @config[:default_field_parse] ||= 'string' # valid values: 'string', 'json'
 
+        # :override_behavior:
+        # Valid values: 'normal', 'flag'
+        # Default: 'normal'
+        # If set to 'flag' a read from vault will only be done if the override parameter
+        # is a hash, and it contains the 'flag', it will behave like this:
+        # - when the value of the 'flag' key is 'vault', it will look in vault
+        # - when the value is 'vault_only', it will return the default or raise an exception
+        #   if the lookup key is not found in vault
+        # If the 'flag' key does not exist, or if the override parameter is not a hash,
+        # nil will be returned to signal that the next backend should be searched.
+        # If the hash contains the 'override' key, its value will be used as the actual
+        # override.
+        # To support the 'flag' behavior, the `hiera_vault`, `hiera_vault_array`, and
+        # `hiera_vault_hash` functions need to be used, since they will make sure the
+        # override parameter is checked and changed where needed
+        # Additionally, when 'vault_only' is used, it will only work properly using the
+        # special hiera_vault* functions
+        #
+        # The 'flag_default' setting can be used to set the default for the 'flag' element
+        # to 'vault_only'. This is handled by the hiera_vault* parser functions.
+        #
+        @config[:override_behavior] ||= 'normal'
+        if not ['normal','flag'].include?(@config[:override_behavior])
+          raise Exception, "[hiera-vault] invalid value for :override_behavior: '#{@config[:override_behavior]}', should be one of 'normal','flag'"
+        end
+
+        @config[:flag_default] ||= 'vault_first'
+        if not ['vault_first','vault_only'].include?(@config[:flag_default])
+          raise Exception, "hiera_vault: invalid value '#{@config[:flag_default]}' for :flag_default in hiera config, one of 'vault_first', 'vault_only' expected"
+        end
+
+        @config[:default_field_parse] ||= 'string' # valid values: 'string', 'json'
         if not ['string','json'].include?(@config[:default_field_parse])
           raise Exception, "[hiera-vault] invalid value for :default_field_parse: '#{@config[:default_field_behavior]}', should be one of 'string','json'"
         end
@@ -20,75 +53,163 @@ def initialize()
         #   'ignore' => ignore additional fields, if the field is not present return nil
         #   'only'   => only return value of default_field when it is present and the only field, otherwise return hash as normal
         @config[:default_field_behavior] ||= 'ignore'
-
         if not ['ignore','only'].include?(@config[:default_field_behavior])
           raise Exception, "[hiera-vault] invalid value for :default_field_behavior: '#{@config[:default_field_behavior]}', should be one of 'ignore','only'"
         end
 
+        vault_connect
+      end
+
+      def lookup(key, scope, order_override, resolution_type)
         begin
-          @vault = Vault::Client.new
-          @vault.configure do |config|
-            config.address = @config[:addr] if @config[:addr]
-            config.token = @config[:token] if @config[:token]
-            config.ssl_pem_file = @config[:ssl_pem_file] if @config[:ssl_pem_file]
-            config.ssl_verify = @config[:ssl_verify] if @config[:ssl_verify]
-            config.ssl_ca_cert = @config[:ssl_ca_cert] if config.respond_to? :ssl_ca_cert
-            config.ssl_ca_path = @config[:ssl_ca_path] if config.respond_to? :ssl_ca_path
-            config.ssl_ciphers = @config[:ssl_ciphers] if config.respond_to? :ssl_ciphers
+          vault_connect
+
+          read_vault = false
+          genpw = false
+          otp = nil
+
+          if @config[:override_behavior] == 'flag'
+            if order_override.kind_of? Hash
+              if order_override.has_key?('flag')
+                if ['vault_default','vault_first','vault_only'].include?(order_override['flag'])
+                  read_vault = true
+                  if order_override['flag'] == 'vault_default'
+                    # since variables are passed by reference, the caller will know afterwards, which flag was actually used
+                    order_override['flag'] = @config[:flag_default]
+                  end
+                  if order_override.has_key?('generate')
+                    pwlen = order_override['generate'].to_i
+                    if pwlen > 8 # TODO: make configurable
+                      genpw = true
+                    end
+                  end
+                  if order_override.has_key?('vault_otp')
+                    otp = order_override['vault_otp']
+                  end
+                  if order_override.has_key?('resolution_type')
+                    resolution_type = order_override['resolution_type']
+                  end
+                  # this one must be last, because order_override gets a new value!:
+                  if order_override.has_key?('override')
+                    order_override = order_override['override']
+                  else
+                    order_override = nil
+                  end
+                else
+                  raise Exception, "[hiera-vault] Invalid value '#{order_override['flag']}' for 'flag' element in override parameter, expected one of ['vault_default', 'vault_first', 'vault_only'], while override_behavior is 'flag'"
+                end
+                if @vault.nil?
+                  raise Exception, "[hiera-vault] Cannot skip, because vault is unavailable and vault must be read, while override_behavior is 'flag'"
+                end
+              else
+                Hiera.debug("[hiera-vault] Not reading from vault, because 'flag' element does not exist in override parameter, while override_behavior is 'flag'")
+              end
+            else
+              Hiera.debug("[hiera-vault] Not reading from vault, because override parameter is not a hash, while override_behavior is 'flag'")
+            end
+          else
+            # normal behavior
+            return nil if @vault.nil?
+            read_vault = true
           end
 
-          fail if @vault.sys.seal_status.sealed?
-          Hiera.debug("[hiera-vault] Client configured to connect to #{@vault.address}")
+          answer = nil
+
+          if read_vault
+            Hiera.debug("[hiera-vault] Looking up #{key} in vault backend")
+
+            found = false
+
+            # Only generic mounts supported so far
+            @config[:mounts][:generic].each do |mount|
+              path = Backend.parse_string(mount, scope, { 'key' => key })
+              Backend.datasources(scope, order_override) do |source|
+                Hiera.debug("Looking in path #{path}/#{source}/")
+                new_answer = lookup_generic("#{path}/#{source}/#{key}", scope)
+                #Hiera.debug("[hiera-vault] Answer: #{new_answer}:#{new_answer.class}")
+                next if new_answer.nil?
+                case resolution_type
+                when :array
+                  raise Exception, "Hiera type mismatch: expected Array and got #{new_answer.class}" unless new_answer.kind_of? Array or new_answer.kind_of? String
+                  answer ||= []
+                  answer << new_answer
+                when :hash
+                  raise Exception, "Hiera type mismatch: expected Hash and got #{new_answer.class}" unless new_answer.kind_of? Hash
+                  answer ||= {}
+                  answer = Backend.merge_answer(new_answer,answer)
+                else
+                  answer = new_answer
+                  found = true
+                  break
+                end
+              end
+
+              break if found
+            end
+          end
+
+          if answer.nil? and @config[:default_field] and genpw
+            new_answer = generate(pwlen)
+
+            @config[:mounts][:generic].each do |mount|
+              path = Backend.parse_string(mount, scope, { 'key' => key })
+              Backend.datasources(scope, order_override) do |source|
+                # Storing the generated secret in the override path or the highest path in the hierarchy
+                # make sure to use a proper override or an appropriate hierarchy if the secret is to be used
+                # on different nodes, otherwise the same key might be written with a different value at different
+                # paths
+                Hiera.debug("Storing generated secret in vault at path #{path}/#{source}/#{key}")
+                answer = new_answer if store("#{path}/#{source}/#{key}", { @config[:default_field].to_sym => new_answer })
+                break
+              end
+              break
+            end
+          end
+          if answer.nil? and not otp.nil?
+            answer = otp
+          end
+          return answer
         rescue Exception => e
-          @vault = nil
-          Hiera.warn("[hiera-vault] Skipping backend. Configuration error: #{e}")
+          raise Exception, "#{e.message} in #{e.backtrace[0]}"
         end
       end
 
-      def lookup(key, scope, order_override, resolution_type)
-        return nil if @vault.nil?
-
-        Hiera.debug("[hiera-vault] Looking up #{key} in vault backend")
-
-        answer = nil
-        found = false
-
-        # Only generic mounts supported so far
-        @config[:mounts][:generic].each do |mount|
-          path = Backend.parse_string(mount, scope, { 'key' => key })
-          Backend.datasources(scope, order_override) do |source|
-            Hiera.debug("Looking in path #{path}/#{source}/")
-            new_answer = lookup_generic("#{path}/#{source}/#{key}", scope)
-            #Hiera.debug("[hiera-vault] Answer: #{new_answer}:#{new_answer.class}")
-            next if new_answer.nil?
-            case resolution_type
-            when :array
-              raise Exception, "Hiera type mismatch: expected Array and got #{new_answer.class}" unless new_answer.kind_of? Array or new_answer.kind_of? String
-              answer ||= []
-              answer << new_answer
-            when :hash
-              raise Exception, "Hiera type mismatch: expected Hash and got #{new_answer.class}" unless new_answer.kind_of? Hash
-              answer ||= {}
-              answer = Backend.merge_answer(new_answer,answer)
-            else
-              answer = new_answer
-              found = true
-              break
+      def vault_connect
+        if @vault.nil?
+          begin
+            @vault = Vault::Client.new
+            @vault.configure do |config|
+              config.address = @config[:addr] if @config[:addr]
+              config.token = @config[:token] if @config[:token]
+              config.ssl_pem_file = @config[:ssl_pem_file] if @config[:ssl_pem_file]
+              config.ssl_verify = @config[:ssl_verify] if @config[:ssl_verify]
+              config.ssl_ca_cert = @config[:ssl_ca_cert] if config.respond_to? :ssl_ca_cert
+              config.ssl_ca_path = @config[:ssl_ca_path] if config.respond_to? :ssl_ca_path
+              config.ssl_ciphers = @config[:ssl_ciphers] if config.respond_to? :ssl_ciphers
             end
+
+            fail if @vault.sys.seal_status.sealed?
+            Hiera.debug("[hiera-vault] Client configured to connect to #{@vault.address}")
+          rescue Exception => e
+            @vault = nil
+            Hiera.warn("[hiera-vault] Skipping backend. Configuration error: #{e}")
+          end
+        end
+        if @vault
+          begin
+            fail if @vault.sys.seal_status.sealed?
+          rescue Exception => e
+            @vault = nil
+            Hiera.warn("[hiera-vault] Vault is unavailable or configuration error: #{e}")
           end
-          break if found
         end
-
-        return answer
       end
 
       def lookup_generic(key, scope)
           begin
             secret = @vault.logical.read(key)
-          rescue Vault::HTTPConnectionError
-            Hiera.debug("[hiera-vault] Could not connect to read secret: #{key}")
-          rescue Vault::HTTPError => e
-            Hiera.warn("[hiera-vault] Could not read secret #{key}: #{e.errors.join("\n").rstrip}")
+          rescue Exception => e
+            raise Exception, "[hiera-vault] Could not read secret #{key}, #{e.class}: #{e.errors.join("\n").rstrip}"
           end
 
           return nil if secret.nil?
@@ -101,8 +222,8 @@ def lookup_generic(key, scope)
             if @config[:default_field_parse] == 'json'
               begin
                 data = JSON.parse(data)
-              rescue JSON::ParserError => e
-                Hiera.debug("[hiera-vault] Could not parse string as json: #{e}")
+              rescue JSON::ParserError
+                Hiera.debug("[hiera-vault] Could not parse string as JSON")
               end
             end
           else
@@ -114,6 +235,33 @@ def lookup_generic(key, scope)
           return Backend.parse_answer(data, scope)
       end
 
+      def generate(password_size)
+        pass = ""
+        (1..password_size).each do
+          pass += (("a".."z").to_a+("A".."Z").to_a+("0".."9").to_a)[rand(62).to_int]
+        end
+
+        pass
+      end
+
+      def store(key, secret_hash)
+          begin
+            write_result = @vault.logical.write(key, secret_hash)
+          rescue Vault::HTTPConnectionError
+            Hiera.debug("[hiera-vault] Could not connect to write secret: #{key}")
+          rescue Vault::HTTPError => e
+            Hiera.warn("[hiera-vault] Could not write secret #{key}: #{e.errors.join("\n").rstrip}")
+          end
+
+          if write_result == true
+            Hiera.debug("[hiera-vault] Successfully written secret: #{key}")
+            return true
+          else
+            Hiera.warn("[hiera-vault] Could not write secret #{key}: #{write_result}")
+            return false
+          end
+      end
+
     end
   end
 end
diff --git a/lib/hiera_vault.rb b/lib/hiera_vault.rb
new file mode 100644
index 0000000..d3875bd
--- /dev/null
+++ b/lib/hiera_vault.rb
@@ -0,0 +1,122 @@
+require 'hiera_puppet'
+
+module HieraVault
+
+  module_function
+  def lookup(key, default, scope, override, resolution_type)
+    begin
+      flag_default = 'vault_default'
+      override ||= {'flag' => flag_default}
+      case override.class.to_s
+      when 'String'
+        override = {'flag' => flag_default, 'override' => override}
+      when 'Hash'
+        if not override.has_key?('flag')
+          override['flag'] = flag_default
+        end
+      else
+        raise(Puppet::ParseError, "hiera_vault: invalid 'override' parameter supplied: '#{override}':#{override.class}")
+      end
+
+      if resolution_type == :priority
+        if default.kind_of? Hash
+          if default.has_key?('generate')
+            override['generate'] = default['generate'].to_i
+            default = nil
+          end
+        end
+      end
+
+      r = rand(2147483647).to_s
+      otp = "vault_otp_#{r}"
+      case resolution_type
+      when :array
+        otp = [otp]
+      when :hash
+        otp = {'otp' => otp}
+      end
+      override['vault_otp'] = otp
+
+      # this is for vault_backend so that it will use the actual resolution type internally
+      override['resolution_type'] = resolution_type
+
+      new_answer = HieraPuppet.lookup(key, nil, scope, override, :priority)
+      if new_answer == otp
+        # this means that vault_backend could not find anything, so it returned the value of vault_otp
+        new_answer = nil
+      end
+
+      if new_answer.nil?
+        answer = nil
+      else
+        case resolution_type
+        when :array
+          raise Puppet::ParseError, "hiera_vault: after vault_backend.lookup: type mismatch: expected Array and got #{new_answer.class}" unless new_answer.kind_of? Array or new_answer.kind_of? String
+          answer ||= []
+          answer << new_answer
+        when :hash
+          raise Puppet::ParseError, "hiera_vault: after vault_backend.lookup: type mismatch: expected Hash and got #{new_answer.class}" unless new_answer.kind_of? Hash
+          answer ||= {}
+          answer = Hiera::Backend.merge_answer(new_answer,answer)
+        else
+          answer = new_answer
+        end
+      end
+
+      hiera_scope = Hiera::Scope.new(scope)
+      if override['flag'] == 'vault_only'
+        if not (default.nil? or default.empty?)
+          answer = Hiera::Backend.resolve_answer(answer, resolution_type) unless answer.nil?
+          answer = Hiera::Backend.parse_string(default, hiera_scope) if answer.nil? and default.is_a?(String)
+          answer = default if answer.nil?
+        end
+        if answer.nil?
+          raise(Puppet::ParseError, "hiera_vault: Could not find data item #{key} in vault, while vault_only was requested, and empty default supplied")
+        end
+        return answer
+      end
+
+      if answer.nil? or resolution_type != :priority
+        # continue with normal hiera lookup, while vault_backend will skip automatically
+        if override.has_key?('override')
+          override = override['override']
+        else
+          override = nil
+        end
+
+        begin
+          new_answer = HieraPuppet.lookup(key, nil, scope, override, resolution_type)
+        rescue Puppet::ParseError
+          if answer.nil?
+            if default.nil? or default.empty?
+              raise(Puppet::ParseError, "Could not find data item #{key} in vault and in any Hiera data file and no or empty default supplied")
+            end
+            answer = Hiera::Backend.parse_string(default, hiera_scope) if default.is_a?(String)
+            answer = default if answer.nil?
+            return answer
+          end
+        end
+      end
+      if not new_answer.nil?
+        case resolution_type
+        when :array
+          raise Puppet::ParseError, "hiera_vault: after normal Hiera lookup: type mismatch: expected Array and got #{new_answer.class}" unless new_answer.nil? or new_answer.kind_of? Array or new_answer.kind_of? String
+          answer ||= []
+          answer << new_answer
+        when :hash
+          raise Puppet::ParseError, "hiera_vault: after normal Hiera lookup: type mismatch: expected Hash and got #{new_answer.class}" unless new_answer.kind_of? Hash
+          answer ||= {}
+          answer = Hiera::Backend.merge_answer(new_answer,answer)
+        else
+          answer = new_answer
+        end
+      end
+      answer = Hiera::Backend.resolve_answer(answer, resolution_type)
+      return answer
+    rescue Exception => e
+      raise(Puppet::ParseError, "#{e.message} in #{e.backtrace[0]}")
+    end
+  end
+
+end
+
diff --git a/lib/puppet/parser/functions/hiera_vault.rb b/lib/puppet/parser/functions/hiera_vault.rb
new file mode 100644
index 0000000..ce3920f
--- /dev/null
+++ b/lib/puppet/parser/functions/hiera_vault.rb
@@ -0,0 +1,17 @@
+require 'hiera_puppet'
+require 'hiera_vault'
+
+module Puppet::Parser::Functions
+  newfunction(:hiera_vault, :type => :rvalue, :arity => -2, :doc => "Performs a
+  hiera lookup, first and optionally only in the 'vault' backend.
+
+  The behavior depends on the 'override' parameter.
+
+  NOTICE: For this function to work properly, set :override_behavior: 'flag' in the
+  :vault: config part in the hiera config.
+  ") do |*args|
+    key, default, override = HieraPuppet.parse_args(args)
+    HieraVault.lookup(key, default, self, override, :priority)
+  end
+end
+
diff --git a/lib/puppet/parser/functions/hiera_vault_array.rb b/lib/puppet/parser/functions/hiera_vault_array.rb
new file mode 100644
index 0000000..a281246
--- /dev/null
+++ b/lib/puppet/parser/functions/hiera_vault_array.rb
@@ -0,0 +1,17 @@
+require 'hiera_puppet'
+require 'hiera_vault'
+
+module Puppet::Parser::Functions
+  newfunction(:hiera_vault_array, :type => :rvalue, :arity => -2, :doc => "Performs a
+  hiera_array lookup, first and optionally only in the 'vault' backend.
+
+  The behavior depends on the 'override' parameter.
+
+  NOTICE: For this function to work properly, set :override_behavior: 'flag' in the
+  :vault: config part in the hiera config.
+  ") do |*args|
+    key, default, override = HieraPuppet.parse_args(args)
+    HieraVault.lookup(key, default, self, override, :array)
+  end
+end
+
diff --git a/lib/puppet/parser/functions/hiera_vault_hash.rb b/lib/puppet/parser/functions/hiera_vault_hash.rb
new file mode 100644
index 0000000..e2c85bb
--- /dev/null
+++ b/lib/puppet/parser/functions/hiera_vault_hash.rb
@@ -0,0 +1,17 @@
+require 'hiera_puppet'
+require 'hiera_vault'
+
+module Puppet::Parser::Functions
+  newfunction(:hiera_vault_hash, :type => :rvalue, :arity => -2, :doc => "Performs a
+  hiera_hash lookup, first and optionally only in the 'vault' backend.
+
+  The behavior depends on the 'override' parameter.
+
+  NOTICE: For this function to work properly, set :override_behavior: 'flag' in the
+  :vault: config part in the hiera config.
+  ") do |*args|
+    key, default, override = HieraPuppet.parse_args(args)
+    HieraVault.lookup(key, default, self, override, :hash)
+  end
+end
+