Etcd service watcher

Gemfile

@@ -1,4 +1,6 @@
 source 'https://rubygems.org'
 
+gem 'docker-api', :require => 'docker'
+
 # Specify your gem's dependencies in synapse.gemspec
 gemspec

Gemfile.lock

@@ -4,6 +4,7 @@ PATH
     synapse (0.12.1)
       aws-sdk (~> 1.39)
       docker-api (~> 1.7.2)
+      etcd (~> 0.2.4)
       zk (~> 1.9.4)
 
 GEM
@@ -21,6 +22,8 @@ GEM
       archive-tar-minitar
       excon (>= 0.28)
       json
+    etcd (0.2.4)
+      mixlib-log
     excon (0.45.4)
     ffi (1.9.3-java)
     json (1.8.3)
@@ -30,6 +33,7 @@ GEM
       multi_json (>= 1.8.4)
     method_source (0.8.2)
     mini_portile (0.6.2)
+    mixlib-log (1.6.0)
     multi_json (1.11.2)
     nokogiri (1.6.6.2)
       mini_portile (~> 0.6.0)
@@ -70,11 +74,9 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
+  docker-api
   pry
   pry-nav
   rake
   rspec (~> 3.1.0)
   synapse!
-
-BUNDLED WITH
-   1.10.5

README.md

@@ -186,6 +186,16 @@ be used in preference to the `AWS_` environment variables.
 * `aws_secret_access_key`: AWS secret key or set `AWS_SECRET_ACCESS_KEY` in the environment.
 * `aws_region`: AWS region (i.e. `us-east-1`) or set `AWS_REGION` in the environment.
 
+##### etcd #####
+
+This watcher retrieves a list from etcd, similarly to the zookeeper watcher
+
+It takes the following options:
+
+* `method`: etcd
+* `hosts`: A list of etcd hosts to connect to, in the format "host" or "host:port"
+* `path`: The path to create in etcd where ephemeral nodes will be created for each available service server
+
 #### Listing Default Servers ####
 
 You may list a number of default servers providing a service.

lib/synapse/service_watcher.rb

@@ -3,6 +3,7 @@
 
 module Synapse
   class ServiceWatcher
+
     # the method which actually dispatches watcher creation requests
     def self.create(name, opts, synapse)
       opts['name'] = name
@@ -24,3 +25,4 @@ def self.create(name, opts, synapse)
     end
   end
 end
+

lib/synapse/service_watcher/etcd.rb

@@ -0,0 +1,166 @@
+require "synapse/service_watcher/base"
+
+require 'etcd'
+
+module Synapse
+  class EtcdWatcher < BaseWatcher
+    NUMBERS_RE = /^\d+$/
+
+    def start
+      @etcd_hosts = @discovery['hosts'].shuffle
+
+      log.info "synapse: starting etcd watcher #{@name} @ hosts: #{@discovery['hosts']}, 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 hosts for service #{@name}" \
+        unless @discovery['hosts']
+      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 an etcd 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

@@ -17,8 +17,9 @@ Gem::Specification.new do |gem|
   gem.test_files    = gem.files.grep(%r{^(test|spec|features)/})
 
   gem.add_runtime_dependency "aws-sdk", "~> 1.39"
-  gem.add_runtime_dependency "docker-api", "~> 1.7.2"
+  gem.add_runtime_dependency 'docker-api', "~> 1.7.2"
   gem.add_runtime_dependency "zk", "~> 1.9.4"
+  gem.add_runtime_dependency "etcd", "~> 0.2.4"
 
   gem.add_development_dependency "rake"
   gem.add_development_dependency "rspec", "~> 3.1.0"