naive nginx backend configurator

lib/synapse.rb

@@ -5,6 +5,7 @@
 require "synapse/log"
 require "synapse/haproxy"
 require "synapse/file_output"
+require "synapse/nginx_config"
 require "synapse/service_watcher"
 
 
@@ -28,6 +29,7 @@ def initialize(opts={})
       # want to communicate via haproxy, e.g. cassandra
       if opts.has_key?('file_output')
         @config_generators << FileOutput.new(opts['file_output'])
+        @config_generators << NginxConfig.new(opts['file_output'])
       end
 
       # configuration is initially enabled to configure on first loop

lib/synapse/nginx_config.rb

@@ -0,0 +1,59 @@
+require 'fileutils'
+require 'tempfile'
+
+module Synapse
+  class NginxConfig
+    include Logging
+    attr_reader :opts, :name
+
+    def initialize(opts)
+      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 = 'nginx_config'
+    end
+
+    def tick(watchers)
+    end
+
+    def update_config(watchers)
+      watchers.each do |watcher|
+        write_backends_to_file(watcher.name, watcher.backends)
+      end
+      clean_old_watchers(watchers)
+    end
+
+    def write_backends_to_file(service_name, new_backends)
+      data_path = File.join(@opts['output_directory'], "#{service_name}.conf")
+        # Atomically write new sevice configuration file
+        content = "upstream #{service_name} {
+  zone #{service_name} 128k;
+          #{new_backends.map{|b| "server #{b["host"]}:#{b["port"]}; "}.join("\n")}
+}"
+        temp_path = File.join(@opts['output_directory'],
+                              ".#{service_name}.conf.tmp")
+        File.open(temp_path, 'w', 0644) {|f| f.write(content)}
+        FileUtils.mv(temp_path, data_path)
+        return true
+    end
+
+    def clean_old_watchers(current_watchers)
+      # Cleanup old services that Synapse no longer manages
+      FileUtils.cd(@opts['output_directory']) do
+        present_files = Dir.glob('*.conf')
+        managed_files = current_watchers.collect {|watcher| "#{watcher.name}.conf"}
+        files_to_purge = present_files.select {|svc| not managed_files.include?(svc)}
+        log.info "synapse: purging unknown service files #{files_to_purge}" if files_to_purge.length > 0
+        FileUtils.rm(files_to_purge)
+      end
+    end
+  end
+end