Allow registrations to be manifested on the file system and add 'use_previous_backends' option

Gemfile.lock

@@ -62,11 +62,11 @@ GEM
     slyphon-zookeeper_jar (3.3.5-java)
     spoon (0.0.4)
       ffi
-    zk (1.9.4)
+    zk (1.9.5)
       logging (~> 1.8.2)
       zookeeper (~> 1.4.0)
-    zookeeper (1.4.8)
-    zookeeper (1.4.8-java)
+    zookeeper (1.4.10)
+    zookeeper (1.4.10-java)
       slyphon-log4j (= 1.2.15)
       slyphon-zookeeper_jar (= 3.3.5)
 

README.md

@@ -198,6 +198,10 @@ If you do not list any default servers, no proxy will be created.  The
 `default_servers` will also be used in addition to discovered servers if the
 `keep_default_servers` option is set.
 
+If you do not list any `default_servers`, and all backends for a service
+disappear then the previous known backends will be used.  Disable this behavior
+by unsetting `use_previous_backends`.
+
 #### The `haproxy` Section ####
 
 This section is its own hash, which should contain the following keys:
@@ -218,6 +222,7 @@ The `haproxy` section of the config file has the following options:
 * `config_file_path`: where Synapse will write the HAProxy config file
 * `do_writes`: whether or not the config file will be written (default to `true`)
 * `do_reloads`: whether or not Synapse will reload HAProxy (default to `true`)
+* `do_socket`: whether or not Synapse will use the HAProxy socket commands to prevent reloads (default to `true`)
 * `global`: options listed here will be written into the `global` section of the HAProxy config
 * `defaults`: options listed here will be written into the `defaults` section of the HAProxy config
 * `extra_sections`: additional, manually-configured `frontend`, `backend`, or `listen` stanzas
@@ -335,5 +340,5 @@ end
 3. Implement the `start` and `validate_discovery_opts` methods
 4. Implement whatever additional methods your discovery requires
 
-When your watcher detects a list of new backends, they should be written to `@backends`.
-You should then call `@synapse.configure` to force synapse to update the HAProxy config.
+When your watcher detects a list of new backends, you should call `set_backends` to
+store the new backends and update the HAProxy config.

lib/synapse.rb

@@ -1,6 +1,7 @@
 require "synapse/version"
 require "synapse/service_watcher/base"
 require "synapse/haproxy"
+require "synapse/file_output"
 require "synapse/service_watcher"
 require "synapse/log"
 
@@ -17,9 +18,17 @@ def initialize(opts={})
       raise "specify a list of services to connect in the config" unless opts.has_key?('services')
       @service_watchers = create_service_watchers(opts['services'])
 
-      # create the haproxy object
+      # create objects that need to be notified of service changes
+      @config_generators = []
+      # create the haproxy config generator, this is mandatory
       raise "haproxy config section is missing" unless opts.has_key?('haproxy')
-      @haproxy = Haproxy.new(opts['haproxy'])
+      @config_generators << Haproxy.new(opts['haproxy'])
+
+      # possibly create a file manifestation for services that do not
+      # want to communicate via haproxy, e.g. cassandra
+      if opts.has_key?('file_output')
+        @config_generators << FileOutput.new(opts['file_output'])
+      end
 
       # configuration is initially enabled to configure on first loop
       @config_updated = true
@@ -47,10 +56,15 @@ def run
 
         if @config_updated
           @config_updated = false
-          log.info "synapse: regenerating haproxy config"
-          @haproxy.update_config(@service_watchers)
-        else
-          sleep 1
+          @config_generators.each do |config_generator|
+            log.info "synapse: configuring #{config_generator.name}"
+            config_generator.update_config(@service_watchers)
+          end
+        end
+
+        sleep 1
+        @config_generators.each do |config_generator|
+          config_generator.tick(@service_watchers)
         end
 
         loops += 1

lib/synapse/file_output.rb

@@ -0,0 +1,56 @@
+require 'synapse/log'
+require 'fileutils'
+require 'tempfile'
+
+module Synapse
+  class FileOutput
+    include Logging
+    attr_reader :opts, :name
+
+    def initialize(opts)
+      super()
+
+      unless opts.has_key?("output_directory")
+        raise ArgumentError, "flat file generation requires an output_directory key"
+      end
+
+      begin
+        FileUtils.mkdir_p(opts['output_directory'])
+      rescue SystemCallError => err
+        raise ArgumentError, "provided output directory #{opts['output_directory']} is not present or creatable"
+      end
+
+      @opts = opts
+      @name = 'file_output'
+    end
+
+    def tick(watchers)
+    end
+
+    def update_config(watchers)
+      watchers.each do |watcher|
+        write_backends_to_file(watcher.name, watcher.backends)
+      end
+    end
+
+    def write_backends_to_file(service_name, new_backends)
+      data_path = File.join(@opts['output_directory'], "#{service_name}.json")
+      begin
+        old_backends = JSON.load(File.read(data_path))
+      rescue Errno::ENOENT
+        old_backends = nil
+      end
+
+      if old_backends == new_backends
+        return false
+      else
+        # Atomically write new sevice configuration file
+        temp_path = File.join(@opts['output_directory'],
+                              ".#{service_name}.json.tmp")
+        File.open(temp_path, 'w', 0644) {|f| f.write(new_backends.to_json)}
+        FileUtils.mv(temp_path, data_path)
+        return true
+      end
+    end
+  end
+end