agent: first pass at service maintenance mode

command/agent/agent.go

@@ -29,6 +29,9 @@ const (
 		"If Consul was not shut down properly, the socket file may " +
 		"be left behind. If the path looks correct, remove the file " +
 		"and try again."
+
+	// The ID of the faux health check for maintenance mode
+	maintCheckID = "_maintenance_"
 )
 
 /*
@@ -995,3 +998,66 @@ func (a *Agent) unloadChecks() error {
 
 	return nil
 }
+
+func (a *Agent) EnableServiceMaintenance(serviceID string) error {
+	var service *structs.NodeService
+	for _, svc := range a.state.Services() {
+		if svc.ID == serviceID {
+			service = svc
+		}
+	}
+
+	// Ensure the service exists
+	if service == nil {
+		return fmt.Errorf("No service registered with ID %q", serviceID)
+	}
+
+	// Ensure maintenance mode is not already enabled
+	for _, check := range a.state.Checks() {
+		if check.CheckID == maintCheckID {
+			return fmt.Errorf("Maintenance mode already enabled for service %q", serviceID)
+		}
+	}
+
+	// Create and register the critical health check
+	check := &structs.HealthCheck{
+		Node:        a.config.NodeName,
+		CheckID:     maintCheckID,
+		Name:        "Service Maintenance Mode",
+		Notes:       "Maintenance mode is enabled for this service",
+		ServiceID:   service.ID,
+		ServiceName: service.Service,
+		Status:      structs.HealthCritical,
+	}
+	a.state.AddCheck(check)
+
+	return nil
+}
+
+func (a *Agent) DisableServiceMaintenance(serviceID string) error {
+	var service *structs.NodeService
+	for _, svc := range a.state.Services() {
+		if svc.ID == serviceID {
+			service = svc
+		}
+	}
+
+	// Ensure the service exists
+	if service == nil {
+		return fmt.Errorf("No service registered with ID %q", serviceID)
+	}
+
+	// Ensure maintenance mode is enabled
+	for _, check := range a.state.Checks() {
+		if check.CheckID == maintCheckID {
+			goto DEREGISTER
+		}
+	}
+	return fmt.Errorf("Maintenance mode not enabled for service %q", serviceID)
+
+DEREGISTER:
+	// Deregister the maintenance check
+	a.state.RemoveCheck(maintCheckID)
+
+	return nil
+}

command/agent/agent_endpoint.go

@@ -176,3 +176,40 @@ func (s *HTTPServer) AgentDeregisterService(resp http.ResponseWriter, req *http.
 	serviceID := strings.TrimPrefix(req.URL.Path, "/v1/agent/service/deregister/")
 	return nil, s.agent.RemoveService(serviceID, true)
 }
+
+func (s *HTTPServer) AgentServiceMaintenance(resp http.ResponseWriter, req *http.Request) (interface{}, error) {
+	// Ensure we have a service ID
+	serviceID := strings.TrimPrefix(req.URL.Path, "/v1/agent/service/maintenance/")
+	if serviceID == "" {
+		resp.WriteHeader(400)
+		resp.Write([]byte("Missing service ID"))
+		return nil, nil
+	}
+
+	// Ensure we have some action
+	params := req.URL.Query()
+	if _, ok := params["enable"]; !ok {
+		resp.WriteHeader(400)
+		resp.Write([]byte("Missing value for enable"))
+		return nil, nil
+	}
+
+	var enable bool
+	raw := params.Get("enable")
+	switch raw {
+	case "true":
+		enable = true
+	case "false":
+		enable = false
+	default:
+		resp.WriteHeader(400)
+		resp.Write([]byte(fmt.Sprintf("Invalid value for enable: %q", raw)))
+		return nil, nil
+	}
+
+	if enable {
+		return nil, s.agent.EnableServiceMaintenance(serviceID)
+	} else {
+		return nil, s.agent.DisableServiceMaintenance(serviceID)
+	}
+}

command/agent/http.go

@@ -195,6 +195,7 @@ func (s *HTTPServer) registerHandlers(enableDebug bool) {
 
 	s.mux.HandleFunc("/v1/agent/service/register", s.wrap(s.AgentRegisterService))
 	s.mux.HandleFunc("/v1/agent/service/deregister/", s.wrap(s.AgentDeregisterService))
+	s.mux.HandleFunc("/v1/agent/service/maintenance/", s.wrap(s.AgentServiceMaintenance))
 
 	s.mux.HandleFunc("/v1/event/fire/", s.wrap(s.EventFire))
 	s.mux.HandleFunc("/v1/event/list", s.wrap(s.EventList))