teleport/lib/srv/server/watcher.go

/*
Copyright 2022 Gravitational, Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package server

import (
	"context"
	"time"

	"github.com/gravitational/trace"
	log "github.com/sirupsen/logrus"
)

// Instances contains information about discovered cloud instances from any provider.
type Instances struct {
	*EC2Instances
	*AzureInstances
}

// Fetcher fetches instances from a particular cloud provider.
type Fetcher interface {
	// GetInstances gets a list of cloud instances.
	GetInstances(context.Context) ([]Instances, error)
}

// Watcher allows callers to discover cloud instances matching specified filters.
type Watcher struct {
	// InstancesC can be used to consume newly discovered instances.
	InstancesC chan Instances

	fetchers      []Fetcher
	fetchInterval time.Duration
	ctx           context.Context
	cancel        context.CancelFunc
}

// Run starts the watcher's main watch loop.
func (w *Watcher) Run() {
	ticker := time.NewTicker(w.fetchInterval)
	defer ticker.Stop()
	for {
		for _, fetcher := range w.fetchers {
			instancesColl, err := fetcher.GetInstances(w.ctx)
			if err != nil {
				if trace.IsNotFound(err) {
					continue
				}
				log.WithError(err).Error("Failed to fetch instances")
				continue
			}
			for _, inst := range instancesColl {
				select {
				case w.InstancesC <- inst:
				case <-w.ctx.Done():
				}
			}
		}
		select {
		case <-ticker.C:
			continue
		case <-w.ctx.Done():
			return
		}
	}
}

// Stop stops the watcher.
func (w *Watcher) Stop() {
	w.cancel()
}