diff --git a/lib/synapse/service_watcher/ec2tag.rb b/lib/synapse/service_watcher/ec2tag.rb
index 43f3e192..9df77490 100644
--- a/lib/synapse/service_watcher/ec2tag.rb
+++ b/lib/synapse/service_watcher/ec2tag.rb
@@ -41,15 +41,18 @@ def validate_discovery_opts
           "Missing server_port_override for service #{@name} - which port are backends listening on?"
       end
 
-      unless @haproxy['server_port_override'].match(/^\d+$/)
+      unless @haproxy['server_port_override'].to_s.match(/^\d+$/)
         raise ArgumentError, "Invalid server_port_override value"
       end
 
-      # Required, but can use well-known environment variables.
-      %w[aws_access_key_id aws_secret_access_key aws_region].each do |attr|
-        unless (@discovery[attr] || ENV[attr.upcase])
-          raise ArgumentError, "Missing #{attr} option or #{attr.upcase} environment variable"
-        end
+      # aws region is optional in the SDK, aws will use a default value if not provided
+      unless @discovery['aws_region'] || ENV['AWS_REGION']
+        log.info "aws region is missing, will use default"
+      end
+      # access key id & secret are optional, might be using IAM instance profile for credentials
+      unless ((@discovery['aws_access_key_id'] || ENV['aws_access_key_id']) \
+              && (@discovery['aws_secret_access_key'] || ENV['aws_secret_access_key'] ))
+        log.info "aws access key id & secret not set in config or env variables for service #{name}, will attempt to use IAM instance profile"
       end
     end
 
@@ -60,10 +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
 
diff --git a/spec/lib/synapse/service_watcher_ec2tags_spec.rb b/spec/lib/synapse/service_watcher_ec2tags_spec.rb
index 30aeab37..bbcf15bd 100644
--- a/spec/lib/synapse/service_watcher_ec2tags_spec.rb
+++ b/spec/lib/synapse/service_watcher_ec2tags_spec.rb
@@ -87,20 +87,20 @@ def munge_haproxy_arg(name, new_value)
     end
 
     context 'when missing arguments' do
-      it 'complains if aws_region is missing' do
+      it 'does not break if aws_region is missing' do
         expect {
           Synapse::ServiceWatcher::Ec2tagWatcher.new(remove_discovery_arg('aws_region'), mock_synapse)
-        }.to raise_error(ArgumentError, /Missing aws_region/)
+        }.not_to raise_error
       end
-      it 'complains if aws_access_key_id is missing' do
+      it 'does not break if aws_access_key_id is missing' do
         expect {
           Synapse::ServiceWatcher::Ec2tagWatcher.new(remove_discovery_arg('aws_access_key_id'), mock_synapse)
-        }.to raise_error(ArgumentError, /Missing aws_access_key_id/)
+        }.not_to raise_error
       end
-      it 'complains if aws_secret_access_key is missing' do
+      it 'does not break if aws_secret_access_key is missing' do
         expect {
           Synapse::ServiceWatcher::Ec2tagWatcher.new(remove_discovery_arg('aws_secret_access_key'), mock_synapse)
-        }.to raise_error(ArgumentError, /Missing aws_secret_access_key/)
+        }.not_to raise_error
       end
       it 'complains if server_port_override is missing' do
         expect {
@@ -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') }