agent: remove an N^2 check. See #1265

[armon]

In #1265, the theory we have is that there is some O(N^2) stuff happening. This was at least one obvious case of that, might be a partial fix.

[slackpad]

This change LGTM but in the thread and in the HC conversation he said there are no checks registered. I was expecting an n^2 services reconciliation here but I'm not seeing it.

[spheromak]

Just to clarify the code I saw the slowdown on was registering a TTL check.

Here is the method I have been using to register a service:

func (b *Binding) Register(client *discovery.ConsulClient) error {
    log.Println("registering binding ", b.UUID)
    siteServiceName := fmt.Sprintf("%s-%s-%s", b.Metadata.Site, b.Metadata.Type, b.Metadata.Environment)

    siteService := &api.AgentServiceRegistration{
      Name: siteServiceName,
      ID:   b.Metadata.Site,
      Tags: []string{b.UUID, b.Metadata.Environment},
      Port: b.Metadata.Port,

      Address: config.Opts.Bind,
    }

    siteCheck := &api.AgentCheckRegistration{
      ID:        b.UUID,
      Name:      fmt.Sprintf("%s-%s", b.Metadata.Type, b.UUID),
      ServiceID: b.Metadata.Site,
    }
    siteCheck.TTL = "15s"

    if err := client.Agent.ServiceRegister(siteService); err != nil {
      return err
    }

    if err := client.RegisterCheck(siteCheck); err != nil {
      return err
    }

    return nil
  }

and the generator:

  //Inject a boatload of bindings up front
  for i := 0; i < 100000; i++ {
    m := binding.Metadata{
      Site:        uniuri.New(),
      Type:        uniuri.New(),
      Environment: uniuri.New(),
      Port:        config.Opts.Port,
      Endpoint:    config.Opts.Bind,
    }

    bindings = append(bindings, binding.Binding{UUID: uuid.New(), Metadata: m})
  }

  for _, b := range bindings {
    if err := b.Register(&c); err != nil {
      log.Fatal(err)
    }
  }