Create an option to stop ignoring weights. By default weights will still

be ignored. This commit is based on:
airbnb#131

but does the following things differently:
1. By default weights are ignored. This is to maintain current behavior
for safety.
2. HAProxy will reconfigure if weights changes.

Author: minkovich

README.md

@@ -261,6 +261,7 @@ This section is its own hash, which should contain the following keys:
 * `listen`: these lines will be parsed and placed in the correct `frontend`/`backend` section as applicable; you can put lines which are the same for the frontend and backend here.
 * `backend_order`: optional: how backends should be ordered in the `backend` stanza. (default is shuffling). Setting to `asc` means sorting backends in ascending alphabetical order before generating stanza. `desc` means descending alphabetical order. `no_shuffle` means no shuffling or sorting.
 * `shared_frontend`: optional: haproxy configuration directives for a shared http frontend (see below)
+* `ignore_weights`: optional: stops haproxy backend 'weight' options being generated, even if the Nerve registrations contain this information. This will cause all backend servers to be treated equally by haproxy. This defaults to true so weights will *NOT* be used by default. 
 
 <a name="haproxy"/>
 ### Configuring HAProxy ###

lib/synapse/haproxy.rb

@@ -535,6 +535,7 @@ def initialize(opts)
       @opts['do_writes'] = true unless @opts.key?('do_writes')
       @opts['do_socket'] = true unless @opts.key?('do_socket')
       @opts['do_reloads'] = true unless @opts.key?('do_reloads')
+      @opts['ignore_weights'] = true unless @opts.key?('ignore_weights')
 
       # how to restart haproxy
       @restart_interval = @opts.fetch('restart_interval', 2).to_i
@@ -741,6 +742,10 @@ def generate_backend_stanza(watcher, config)
           backend = backends[backend_name]
           b = "\tserver #{backend_name} #{backend['host']}:#{backend['port']}"
           b = "#{b} cookie #{backend_name}" unless config.include?('mode tcp')
+          if !@opts['ignore_weights'] && backend.has_key?('weight')
+            weight = backend['weight'].to_i
+            b = "#{b} weight #{weight}"
+          end
           b = "#{b} #{watcher.haproxy['server_options']}" if watcher.haproxy['server_options']
           b = "#{b} #{backend['haproxy_server_options']}" if backend['haproxy_server_options']
           b = "#{b} disabled" unless backend['enabled']

lib/synapse/service_watcher/base.rb

@@ -117,7 +117,7 @@ def set_backends(new_backends)
       # Aggregate and deduplicate all potential backend service instances.
       new_backends = (new_backends + @default_servers) if @keep_default_servers
       new_backends = new_backends.uniq {|b|
-        [b['host'], b['port'], b.fetch('name', '')]
+        [b['host'], b['port'], b.fetch('name', ''), b.fetch('weight', 1)]
       }
 
       if new_backends.to_set == @backends.to_set

spec/lib/synapse/haproxy_spec.rb

@@ -5,15 +5,18 @@ class MockWatcher; end;
 describe Synapse::Haproxy do
   subject { Synapse::Haproxy.new(config['haproxy']) }
 
-  let(:mockwatcher) do
+  def createmockwatcher(backends)
     mockWatcher = double(Synapse::ServiceWatcher)
     allow(mockWatcher).to receive(:name).and_return('example_service')
-    backends = [{ 'host' => 'somehost', 'port' => 5555}]
     allow(mockWatcher).to receive(:backends).and_return(backends)
     allow(mockWatcher).to receive(:haproxy).and_return({'server_options' => "check inter 2000 rise 3 fall 2"})
     mockWatcher
   end
 
+  let(:mockwatcher) do
+    createmockwatcher [{ 'host' => 'somehost', 'port' => '5555'}]
+  end
+
   let(:mockwatcher_with_server_options) do
     mockWatcher = double(Synapse::ServiceWatcher)
     allow(mockWatcher).to receive(:name).and_return('example_service')
@@ -96,4 +99,24 @@ class MockWatcher; end;
     expect(subject.generate_frontend_stanza(mockwatcher_frontend_with_bind_address, mockConfig)).to eql(["\nfrontend example_service", [], "\tbind 127.0.0.3:2200", "\tdefault_backend example_service"])
   end
 
+  it 'generates backend stanza with weight' do
+    mockConfig = []
+    expect(subject.generate_backend_stanza(createmockwatcher([{ 'weight' => 1, 'host' => 'somehost', 'port' => '5555'}]), mockConfig)).to eql(["\nbackend example_service", [], ["\tserver somehost:5555 somehost:5555 cookie somehost:5555 weight 1 check inter 2000 rise 3 fall 2"]])
+  end
+
+  it 'generates backend stanza with bad weight = 0' do
+    mockConfig = []
+    expect(subject.generate_backend_stanza(createmockwatcher([{ 'weight' => 'hi', 'host' => 'somehost', 'port' => '5555'}]), mockConfig)).to eql(["\nbackend example_service", [], ["\tserver somehost:5555 somehost:5555 cookie somehost:5555 weight 0 check inter 2000 rise 3 fall 2"]])
+  end
+
+  it 'generates backend stanza with nil weight = 0' do
+    mockConfig = []
+    expect(subject.generate_backend_stanza(createmockwatcher([{ 'weight' => nil, 'host' => 'somehost', 'port' => '5555'}]), mockConfig)).to eql(["\nbackend example_service", [], ["\tserver somehost:5555 somehost:5555 cookie somehost:5555 weight 0 check inter 2000 rise 3 fall 2"]])
+  end
+
+  it 'generates backend stanza without weight' do
+    mockConfig = []
+    expect(subject.generate_backend_stanza(createmockwatcher([{ 'host' => 'somehost', 'port' => '5555'}]), mockConfig)).to eql(["\nbackend example_service", [], ["\tserver somehost:5555 somehost:5555 cookie somehost:5555 check inter 2000 rise 3 fall 2"]])
+  end
+
 end

spec/lib/synapse/service_watcher_base_spec.rb

@@ -135,5 +135,23 @@ def remove_arg(name)
         expect(subject.backends).to eq(matching_labeled_backends)
       end
     end
+
+    context 'with ignore_weights set to false' do
+      let(:backends)  { [
+        { 'name' => 'server1', 'host' => 'server1', 'port' => 1111, 'weight' => 11 },
+        { 'name' => 'server2', 'host' => 'server2', 'port' => 2222, 'weight' => 22 },
+      ] }
+      let(:non_matching_weight_backends) { [
+        { 'name' => 'server1', 'host' => 'server1', 'port' => 1111, 'weight' => 33 },
+        { 'name' => 'server2', 'host' => 'server2', 'port' => 2222, 'weight' => 22 },
+      ] }
+      it 'updates backends only when weights change' do
+        expect(subject).to receive(:'reconfigure!').exactly(:twice)
+        expect(subject.send(:set_backends, backends)).to equal(true)
+        expect(subject.backends).to eq(backends)
+        expect(subject.send(:set_backends, non_matching_weight_backends)).to equal(true)
+        expect(subject.backends).to eq(non_matching_weight_backends)
+      end
+    end
   end
 end

spec/support/minimum.conf.yaml

@@ -20,6 +20,7 @@ haproxy:
   config_file_path: "/etc/haproxy/haproxy.cfg"
   do_writes: false
   do_reloads: false
+  ignore_weights: false
   global:
     - global_test_option