adds specs for ec2tag watch method, and fixes bug where if an exception

was raised the normal sleep got skipped, so it could get stuck calling
the failing discover instances code in a tight loop every few ms

lib/synapse/service_watcher/ec2tag.rb

@@ -63,10 +63,11 @@ def watch
           if set_backends(discover_instances)
             log.info "synapse: ec2tag watcher backends have changed."
           end
-          sleep_until_next_check(start)
         rescue Exception => e
           log.warn "synapse: error in ec2tag watcher thread: #{e.inspect}"
           log.warn e.backtrace
+        ensure
+          sleep_until_next_check(start)
         end
       end
 

spec/lib/synapse/service_watcher_ec2tags_spec.rb

@@ -89,17 +89,17 @@ def munge_haproxy_arg(name, new_value)
     context 'when missing arguments' do
       it 'does not break if aws_region is missing' do
         expect {
-          Synapse::ServiceWatcher::EC2Watcher.new(remove_discovery_arg('aws_region'), mock_synapse)
+          Synapse::ServiceWatcher::Ec2tagWatcher.new(remove_discovery_arg('aws_region'), mock_synapse)
         }.not_to raise_error
       end
       it 'does not break if aws_access_key_id is missing' do
         expect {
-          Synapse::ServiceWatcher::EC2Watcher.new(remove_discovery_arg('aws_access_key_id'), mock_synapse)
+          Synapse::ServiceWatcher::Ec2tagWatcher.new(remove_discovery_arg('aws_access_key_id'), mock_synapse)
         }.not_to raise_error
       end
       it 'does not break if aws_secret_access_key is missing' do
         expect {
-          Synapse::ServiceWatcher::EC2Watcher.new(remove_discovery_arg('aws_secret_access_key'), mock_synapse)
+          Synapse::ServiceWatcher::Ec2tagWatcher.new(remove_discovery_arg('aws_secret_access_key'), mock_synapse)
         }.not_to raise_error
       end
       it 'complains if server_port_override is missing' do
@@ -122,6 +122,27 @@ def munge_haproxy_arg(name, new_value)
     let(:instance1) { FakeAWSInstance.new }
     let(:instance2) { FakeAWSInstance.new }
 
+    context 'watch' do
+
+      it 'discovers instances, configures backends, then sleeps' do
+        fake_backends = [1,2,3]
+        expect(subject).to receive(:discover_instances).and_return(fake_backends)
+        expect(subject).to receive(:set_backends).with(fake_backends) { subject.stop }
+        expect(subject).to receive(:sleep_until_next_check)
+        subject.send(:watch)
+      end
+
+      it 'sleeps until next check if discover_instances fails' do
+        expect(subject).to receive(:discover_instances) do
+          subject.stop
+          raise "discover failed"
+        end
+        expect(subject).to receive(:sleep_until_next_check)
+        subject.send(:watch)
+      end
+
+    end
+
     context 'using the AWS API' do
       let(:ec2_client) { double('AWS::EC2') }
       let(:instance_collection) { double('AWS::EC2::InstanceCollection') }