Multi-host compatible etcd service watcher

Dockerfile

@@ -0,0 +1,5 @@
+FROM phusion/baseimage:0.9.10
+ENV HOME /root
+CMD ["/sbin/my_init"]
+RUN apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
+

Gemfile.lock

@@ -4,6 +4,7 @@ PATH
     synapse (0.11.1)
       aws-sdk (~> 1.39)
       docker-api (~> 1.7.2)
+      etcd (~> 0.2.3)
       zk (~> 1.9.4)
 
 GEM
@@ -21,6 +22,8 @@ GEM
       json
     excon (0.38.0)
     ffi (1.9.3-java)
+    etcd (0.2.3)
+      mixlib-log
     json (1.8.1)
     json (1.8.1-java)
     little-plugger (1.1.3)
@@ -33,27 +36,27 @@ GEM
     nokogiri (1.6.2.1)
       mini_portile (= 0.6.0)
     nokogiri (1.6.2.1-java)
-    pry (0.9.12.2)
+    pry (0.9.12.6)
       coderay (~> 1.0.5)
+    mixlib-log (1.6.0)
       method_source (~> 0.8)
       slop (~> 3.4)
-    pry (0.9.12.2-java)
-      coderay (~> 1.0.5)
-      method_source (~> 0.8)
-      slop (~> 3.4)
-      spoon (~> 0.0)
     pry-nav (0.2.3)
       pry (~> 0.9.10)
-    rake (10.1.1)
-    rspec (2.14.1)
-      rspec-core (~> 2.14.0)
-      rspec-expectations (~> 2.14.0)
-      rspec-mocks (~> 2.14.0)
-    rspec-core (2.14.5)
-    rspec-expectations (2.14.2)
-      diff-lcs (>= 1.1.3, < 2.0)
-    rspec-mocks (2.14.3)
-    slop (3.4.6)
+    rake (10.3.2)
+    rspec (3.0.0)
+      rspec-core (~> 3.0.0)
+      rspec-expectations (~> 3.0.0)
+      rspec-mocks (~> 3.0.0)
+    rspec-core (3.0.2)
+      rspec-support (~> 3.0.0)
+    rspec-expectations (3.0.2)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.0.0)
+    rspec-mocks (3.0.2)
+      rspec-support (~> 3.0.0)
+    rspec-support (3.0.2)
+    slop (3.5.0)
     slyphon-log4j (1.2.15)
     slyphon-zookeeper_jar (3.3.5-java)
     spoon (0.0.4)
@@ -67,7 +70,6 @@ GEM
       slyphon-zookeeper_jar (= 3.3.5)
 
 PLATFORMS
-  java
   ruby
 
 DEPENDENCIES

lib/synapse/service_watcher.rb

@@ -4,6 +4,7 @@
 require "synapse/service_watcher/dns"
 require "synapse/service_watcher/docker"
 require "synapse/service_watcher/zookeeper_dns"
+require "synapse/service_watcher/etcd"
 
 module Synapse
   class ServiceWatcher
@@ -15,6 +16,7 @@ class ServiceWatcher
       'dns' => DnsWatcher,
       'docker' => DockerWatcher,
       'zookeeper_dns' => ZookeeperDnsWatcher,
+      'etcd' => EtcdWatcher
     }
 
     # the method which actually dispatches watcher creation requests
@@ -32,3 +34,4 @@ def self.create(name, opts, synapse)
     end
   end
 end
+

lib/synapse/service_watcher/etcd.rb

@@ -0,0 +1,187 @@
+require "synapse/service_watcher/base"
+
+require 'etcd'
+
+# Monkeypatch till 91f9e72d6d57ae3760e9266835f404d986072590 gets to rubygems..
+module Etcd
+  module Keys
+    def watch(key, opts = {})
+      params = { wait: true }
+      fail ArgumentError, 'Second argument must be a hash' unless opts.is_a?(Hash)
+      timeout = opts[:timeout] || @read_timeout
+      index = opts[:waitIndex] || opts[:index]
+      params[:waitIndex] = index unless index.nil?
+      params[:consistent] = opts[:consistent] if opts.key?(:consistent)
+      params[:recursive] = opts[:recursive] if opts.key?(:recursive)
+
+      response = api_execute(key_endpoint + key, :get,
+                             timeout: timeout, params: params)
+      Response.from_http_response(response)
+    end
+  end
+end
+
+module Synapse
+  class EtcdWatcher < BaseWatcher
+    NUMBERS_RE = /^\d+$/
+
+    def start
+      @etcd_hosts = @discovery['hosts'].shuffle
+
+      log.info "synapse: starting etcd watcher #{@name} @ host: #{@discovery['host']}, path: #{@discovery['path']}"
+      @should_exit = false
+
+      @etcd_hosts.each do |h|
+        host, port = h.split(':')
+        port = port || 4003
+        @etcd = ::Etcd.client(:host => host, :port => port)
+
+        connected =
+          begin
+            @etcd.leader
+          rescue
+            false
+          end
+
+        break if connected
+      end
+
+      # call the callback to bootstrap the process
+      discover
+      @synapse.reconfigure!
+      @watcher = Thread.new do
+        watch
+      end
+    end
+
+    def stop
+      log.warn "synapse: etcd watcher exiting"
+
+      @should_exit = true
+      @etcd = nil
+
+      log.info "synapse: etcd watcher cleaned up successfully"
+    end
+
+    def ping?
+      @etcd.leader
+    end
+
+    private
+    def validate_discovery_opts
+      raise ArgumentError, "invalid discovery method #{@discovery['method']}" \
+        unless @discovery['method'] == 'etcd'
+      raise ArgumentError, "missing or invalid etcd host for service #{@name}" \
+        unless @discovery['host']
+      raise ArgumentError, "missing or invalid etcd port for service #{@name}" \
+        unless @discovery['port']
+      raise ArgumentError, "invalid etcd path for service #{@name}" \
+        unless @discovery['path']
+    end
+
+    # helper method that ensures that the discovery path exists
+    def create(path)
+      log.debug "synapse: creating etcd path: #{path}"
+      @etcd.create(path, dir: true)
+    end
+
+    def each_node(node)
+      begin
+        host, port, name = deserialize_service_instance(node.value)
+      rescue StandardError => e
+        log.error "synapse: invalid data in etcd node #{node.inspect} at #{@discovery['path']}: #{e} DATA #{node.value}"
+        nil 
+     else
+        server_port = @server_port_override ? @server_port_override : port
+
+        # find the numberic id in the node name; used for leader elections if enabled
+        numeric_id = node.key.split('/').last
+        numeric_id = NUMBERS_RE =~ numeric_id ? numeric_id.to_i : nil
+
+        log.warn "synapse: discovered backend #{name} at #{host}:#{server_port} for service #{@name}"
+        { 'name' => name, 'host' => host, 'port' => server_port, 'id' => numeric_id}
+      end
+    end
+
+    def each_dir(d)
+      new_backends = []
+      d.children.each do |node|
+        if node.directory?
+          new_backends << each_dir(@etcd.get(node.key))
+        else
+          backend = each_node(node)
+          if backend
+            new_backends << backend
+          end
+        end
+      end
+      new_backends.flatten
+    end
+
+    # find the current backends at the discovery path; sets @backends
+    def discover
+      log.info "synapse: discovering backends for service #{@name}"
+
+      d = nil
+      begin
+        d = @etcd.get(@discovery['path'])
+      rescue Etcd::KeyNotFound
+        create(@discovery['path'])
+        d = @etcd.get(@discovery['path'])
+      end
+
+      new_backends = []
+      if d.directory?
+        new_backends = each_dir(d)
+      else
+        log.warn "synapse: path #{@discovery['path']} is not a directory"
+      end
+
+      if new_backends.empty?
+        if @default_servers.empty?
+          log.warn "synapse: no backends and no default servers for service #{@name}; using previous backends: #{@backends.inspect}"
+          false
+        else
+          log.warn "synapse: no backends for service #{@name}; using default servers: #{@default_servers.inspect}"
+          @backends = @default_servers
+          true
+        end
+      else
+        if @backends != new_backends
+          log.info "synapse: discovered #{new_backends.length} backends (including new) for service #{@name}"
+          @backends = new_backends
+          true
+        else
+          log.info "synapse: discovered #{new_backends.length} backends for service #{@name}"
+          false
+        end
+      end
+    end
+
+    def watch
+      while !@should_exit
+        begin
+          @etcd.watch(@discovery['path'], :timeout => 60, :recursive => true)
+        rescue Timeout::Error
+        else
+          if discover
+            @synapse.reconfigure!
+          end
+        end
+      end
+    end
+
+    # decode the data at a zookeeper endpoint
+    def deserialize_service_instance(data)
+      log.debug "synapse: deserializing process data"
+      decoded = JSON.parse(data)
+
+      host = decoded['host'] || (raise ValueError, 'instance json data does not have host key')
+      port = decoded['port'] || (raise ValueError, 'instance json data does not have port key')
+      name = decoded['name'] || nil
+
+      return host, port, name
+    end
+  end
+end
+

synapse.gemspec

@@ -19,6 +19,7 @@ Gem::Specification.new do |gem|
   gem.add_runtime_dependency "aws-sdk", "~> 1.39"
   gem.add_runtime_dependency "docker-api", "~> 1.7.2"
   gem.add_runtime_dependency "zk", "~> 1.9.4"
+  gem.add_runtime_dependency "etcd", "~> 0.2.3"
 
   gem.add_development_dependency "rake"
   gem.add_development_dependency "rspec"