code: private void guaranteeHasAllTargets(TrafficSource trafficSource,
                                        TargetGroup targetGroup,
                                        Collection<TargetDescription> targets,
                                        Collection<BaragonAgentMetadata> baragonAgents) {
      Collection<TargetDescription> targetDescriptions = new HashSet<>();
      for (BaragonAgentMetadata agent : baragonAgents) {
        try {
          if ((trafficSource.getRegisterBy() == RegisterBy.INSTANCE_ID && agent.getEc2().getInstanceId().isPresent())
              || (trafficSource.getRegisterBy() == RegisterBy.PRIVATE_IP && agent.getEc2().getPrivateIp().isPresent())) {
            String id = trafficSource.getRegisterBy() == RegisterBy.INSTANCE_ID ? agent.getEc2().getInstanceId().get() : agent.getEc2().getPrivateIp().get();
            if (agentShouldRegisterInTargetGroup(id, targets)) {
              targetDescriptions.add(new TargetDescription()
                  .withId(id));
              LOG.info("Will register agent {} to target in group {}", agent, targetGroup);
            } else {
              LOG.debug("Agent {} is already registered", agent);
            }
          }
        } catch (Exception exn) {
          LOG.error("Could not create request to register agent {} due to error", agent, exn);
          exceptionNotifier.notify(exn, ImmutableMap.of("agent", agent.toString()));
        }
      }
  
      if (targetDescriptions.isEmpty()) {
        LOG.debug("No new instances to register with target group");
      } else {
        try {
          RegisterTargetsRequest registerTargetsRequest = new RegisterTargetsRequest()
              .withTargetGroupArn(targetGroup.getTargetGroupArn())
              .withTargets(targetDescriptions);
          elbClient.registerTargets(registerTargetsRequest);
          LOG.info("Registered targets {} onto target group {}", targetDescriptions, targetGroup);
        } catch (AmazonClientException acexn) {
          LOG.error("Failed to register targets {} onto target group {}", targetDescriptions, targetGroup);
          exceptionNotifier.notify(acexn, ImmutableMap.of(
              "targets", targetDescriptions.toString(),
              "targetGroup", targetGroup.toString()));
        }
      }
    }
docs: After this method completes, every agent in baragonAgents should be associated with
  a target in the given target group.
  
  @param targetGroup group to register in
  @param baragonAgents agents to be registered