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main.go
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main.go
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package main
import (
"context"
"encoding/json"
"flag"
"io"
"os"
"strings"
etcd "github.com/coreos/etcd/clientv3"
"github.com/coreos/etcd/mvcc/mvccpb"
log "github.com/sirupsen/logrus"
"github.com/moiot/gravity/pkg/utils"
)
// TargetGroup is the target group read by Prometheus.
type TargetGroup struct {
Targets []string `json:"targets,omitempty"`
Labels map[string]string `json:"labels,omitempty"`
}
type (
instances map[string]string
services map[string]instances
)
var (
servicesPrefix = flag.String("prefix", "/services", "etcd path prefix")
etcdServer = flag.String("server", "http://127.0.0.1:2379", "etcd server to connect to")
targetFile = flag.String("target-file", "tgroups.json", "the file that contains the target groups")
)
func main() {
flag.Parse()
client, err := utils.CreateEtcdClient(*etcdServer)
if err != nil {
log.Fatalf("Error on connect etcd: %s", err)
}
var (
srvs = services{}
)
// Perform an initial read of all services.
res, err := client.Get(context.TODO(), *servicesPrefix, etcd.WithPrefix())
if err != nil {
log.Fatalf("Error on initial retrieval: %s", err)
}
for _, kv := range res.Kvs {
srvs.handle(kv, srvs.update)
}
srvs.persist()
updates := client.Watch(context.TODO(), *servicesPrefix, etcd.WithPrefix())
// Apply updates sent on the channel.
for resp := range updates {
for _, res := range resp.Events {
log.Infoln(res.Type, string(res.Kv.Key), string(res.Kv.Value))
h := srvs.update
if res.Type == mvccpb.DELETE {
h = srvs.delete
}
srvs.handle(res.Kv, h)
}
srvs.persist()
}
}
// handle recursively applies the handler h to the nodes in the subtree
// represented by node.
func (srvs services) handle(node *mvccpb.KeyValue, h func(*mvccpb.KeyValue)) {
h(node)
}
// update the services based on the given node.
func (srvs services) update(kv *mvccpb.KeyValue) {
service, instance, url := convert(kv)
insts, ok := srvs[service]
if !ok {
insts = instances{}
}
insts[instance] = url
srvs[service] = insts
}
func convert(kv *mvccpb.KeyValue) (service, instance, url string) {
sp := strings.Split(string(kv.Key), "/")
return sp[2], sp[3], string(kv.Value)
}
// delete services or instances based on the given node.
func (srvs services) delete(kv *mvccpb.KeyValue) {
service, instance, _ := convert(kv)
// Delete the instance from the service.
delete(srvs[service], instance)
if len(srvs[service]) == 0 {
delete(srvs, service)
}
}
// persist writes the current services to disc.
func (srvs services) persist() {
var tgroups []*TargetGroup
// Write files for current services.
for job, instances := range srvs {
var targets []string
for _, addr := range instances {
targets = append(targets, addr)
}
tgroups = append(tgroups, &TargetGroup{
Targets: targets,
Labels: map[string]string{"job": job},
})
}
content, err := json.Marshal(tgroups)
if err != nil {
log.Errorln(err)
return
}
f, err := create(*targetFile)
if err != nil {
log.Errorln(err)
return
}
defer f.Close()
if _, err := f.Write(content); err != nil {
log.Errorln(err)
}
}
type renameFile struct {
*os.File
filename string
}
func (f *renameFile) Close() error {
f.File.Sync()
if err := f.File.Close(); err != nil {
return err
}
return os.Rename(f.File.Name(), f.filename)
}
func create(filename string) (io.WriteCloser, error) {
tmpFilename := filename + ".tmp"
f, err := os.Create(tmpFilename)
if err != nil {
return nil, err
}
rf := &renameFile{
File: f,
filename: filename,
}
return rf, nil
}