forked from moby/libnetwork
/
consul.go
489 lines (411 loc) · 11.6 KB
/
consul.go
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package consul
import (
"crypto/tls"
"errors"
"net/http"
"strings"
"sync"
"time"
"github.com/docker/libkv"
"github.com/docker/libkv/store"
api "github.com/hashicorp/consul/api"
)
const (
// DefaultWatchWaitTime is how long we block for at a
// time to check if the watched key has changed. This
// affects the minimum time it takes to cancel a watch.
DefaultWatchWaitTime = 15 * time.Second
// RenewSessionRetryMax is the number of time we should try
// to renew the session before giving up and throwing an error
RenewSessionRetryMax = 5
)
var (
// ErrMultipleEndpointsUnsupported is thrown when there are
// multiple endpoints specified for Consul
ErrMultipleEndpointsUnsupported = errors.New("consul does not support multiple endpoints")
// ErrSessionRenew is thrown when the session can't be
// renewed because the Consul version does not support sessions
ErrSessionRenew = errors.New("cannot set or renew session for ttl, unable to operate on sessions")
)
// Consul is the receiver type for the
// Store interface
type Consul struct {
sync.Mutex
config *api.Config
client *api.Client
}
type consulLock struct {
lock *api.Lock
renewCh chan struct{}
}
// Register registers consul to libkv
func Register() {
libkv.AddStore(store.CONSUL, New)
}
// New creates a new Consul client given a list
// of endpoints and optional tls config
func New(endpoints []string, options *store.Config) (store.Store, error) {
if len(endpoints) > 1 {
return nil, ErrMultipleEndpointsUnsupported
}
s := &Consul{}
// Create Consul client
config := api.DefaultConfig()
s.config = config
config.HttpClient = http.DefaultClient
config.Address = endpoints[0]
config.Scheme = "http"
// Set options
if options != nil {
if options.TLS != nil {
s.setTLS(options.TLS)
}
if options.ConnectionTimeout != 0 {
s.setTimeout(options.ConnectionTimeout)
}
}
// Creates a new client
client, err := api.NewClient(config)
if err != nil {
return nil, err
}
s.client = client
return s, nil
}
// SetTLS sets Consul TLS options
func (s *Consul) setTLS(tls *tls.Config) {
s.config.HttpClient.Transport = &http.Transport{
TLSClientConfig: tls,
}
s.config.Scheme = "https"
}
// SetTimeout sets the timeout for connecting to Consul
func (s *Consul) setTimeout(time time.Duration) {
s.config.WaitTime = time
}
// Normalize the key for usage in Consul
func (s *Consul) normalize(key string) string {
key = store.Normalize(key)
return strings.TrimPrefix(key, "/")
}
func (s *Consul) renewSession(pair *api.KVPair, ttl time.Duration) error {
// Check if there is any previous session with an active TTL
session, err := s.getActiveSession(pair.Key)
if err != nil {
return err
}
if session == "" {
entry := &api.SessionEntry{
Behavior: api.SessionBehaviorDelete, // Delete the key when the session expires
TTL: (ttl / 2).String(), // Consul multiplies the TTL by 2x
LockDelay: 1 * time.Millisecond, // Virtually disable lock delay
}
// Create the key session
session, _, err = s.client.Session().Create(entry, nil)
if err != nil {
return err
}
lockOpts := &api.LockOptions{
Key: pair.Key,
Session: session,
}
// Lock and ignore if lock is held
// It's just a placeholder for the
// ephemeral behavior
lock, _ := s.client.LockOpts(lockOpts)
if lock != nil {
lock.Lock(nil)
}
}
_, _, err = s.client.Session().Renew(session, nil)
return err
}
// getActiveSession checks if the key already has
// a session attached
func (s *Consul) getActiveSession(key string) (string, error) {
pair, _, err := s.client.KV().Get(key, nil)
if err != nil {
return "", err
}
if pair != nil && pair.Session != "" {
return pair.Session, nil
}
return "", nil
}
// Get the value at "key", returns the last modified index
// to use in conjunction to CAS calls
func (s *Consul) Get(key string) (*store.KVPair, error) {
options := &api.QueryOptions{
AllowStale: false,
RequireConsistent: true,
}
pair, meta, err := s.client.KV().Get(s.normalize(key), options)
if err != nil {
return nil, err
}
// If pair is nil then the key does not exist
if pair == nil {
return nil, store.ErrKeyNotFound
}
return &store.KVPair{Key: pair.Key, Value: pair.Value, LastIndex: meta.LastIndex}, nil
}
// Put a value at "key"
func (s *Consul) Put(key string, value []byte, opts *store.WriteOptions) error {
key = s.normalize(key)
p := &api.KVPair{
Key: key,
Value: value,
}
if opts != nil && opts.TTL > 0 {
// Create or renew a session holding a TTL. Operations on sessions
// are not deterministic: creating or renewing a session can fail
for retry := 1; retry <= RenewSessionRetryMax; retry++ {
err := s.renewSession(p, opts.TTL)
if err == nil {
break
}
if retry == RenewSessionRetryMax {
return ErrSessionRenew
}
}
}
_, err := s.client.KV().Put(p, nil)
return err
}
// Delete a value at "key"
func (s *Consul) Delete(key string) error {
if _, err := s.Get(key); err != nil {
return err
}
_, err := s.client.KV().Delete(s.normalize(key), nil)
return err
}
// Exists checks that the key exists inside the store
func (s *Consul) Exists(key string) (bool, error) {
_, err := s.Get(key)
if err != nil {
if err == store.ErrKeyNotFound {
return false, nil
}
return false, err
}
return true, nil
}
// List child nodes of a given directory
func (s *Consul) List(directory string) ([]*store.KVPair, error) {
pairs, _, err := s.client.KV().List(s.normalize(directory), nil)
if err != nil {
return nil, err
}
if len(pairs) == 0 {
return nil, store.ErrKeyNotFound
}
kv := []*store.KVPair{}
for _, pair := range pairs {
if pair.Key == directory {
continue
}
kv = append(kv, &store.KVPair{
Key: pair.Key,
Value: pair.Value,
LastIndex: pair.ModifyIndex,
})
}
return kv, nil
}
// DeleteTree deletes a range of keys under a given directory
func (s *Consul) DeleteTree(directory string) error {
if _, err := s.List(directory); err != nil {
return err
}
_, err := s.client.KV().DeleteTree(s.normalize(directory), nil)
return err
}
// Watch for changes on a "key"
// It returns a channel that will receive changes or pass
// on errors. Upon creation, the current value will first
// be sent to the channel. Providing a non-nil stopCh can
// be used to stop watching.
func (s *Consul) Watch(key string, stopCh <-chan struct{}) (<-chan *store.KVPair, error) {
kv := s.client.KV()
watchCh := make(chan *store.KVPair)
go func() {
defer close(watchCh)
// Use a wait time in order to check if we should quit
// from time to time.
opts := &api.QueryOptions{WaitTime: DefaultWatchWaitTime}
for {
// Check if we should quit
select {
case <-stopCh:
return
default:
}
// Get the key
pair, meta, err := kv.Get(key, opts)
if err != nil {
return
}
// If LastIndex didn't change then it means `Get` returned
// because of the WaitTime and the key didn't changed.
if opts.WaitIndex == meta.LastIndex {
continue
}
opts.WaitIndex = meta.LastIndex
// Return the value to the channel
// FIXME: What happens when a key is deleted?
if pair != nil {
watchCh <- &store.KVPair{
Key: pair.Key,
Value: pair.Value,
LastIndex: pair.ModifyIndex,
}
}
}
}()
return watchCh, nil
}
// WatchTree watches for changes on a "directory"
// It returns a channel that will receive changes or pass
// on errors. Upon creating a watch, the current childs values
// will be sent to the channel .Providing a non-nil stopCh can
// be used to stop watching.
func (s *Consul) WatchTree(directory string, stopCh <-chan struct{}) (<-chan []*store.KVPair, error) {
kv := s.client.KV()
watchCh := make(chan []*store.KVPair)
go func() {
defer close(watchCh)
// Use a wait time in order to check if we should quit
// from time to time.
opts := &api.QueryOptions{WaitTime: DefaultWatchWaitTime}
for {
// Check if we should quit
select {
case <-stopCh:
return
default:
}
// Get all the childrens
pairs, meta, err := kv.List(directory, opts)
if err != nil {
return
}
// If LastIndex didn't change then it means `Get` returned
// because of the WaitTime and the child keys didn't change.
if opts.WaitIndex == meta.LastIndex {
continue
}
opts.WaitIndex = meta.LastIndex
// Return children KV pairs to the channel
kvpairs := []*store.KVPair{}
for _, pair := range pairs {
if pair.Key == directory {
continue
}
kvpairs = append(kvpairs, &store.KVPair{
Key: pair.Key,
Value: pair.Value,
LastIndex: pair.ModifyIndex,
})
}
watchCh <- kvpairs
}
}()
return watchCh, nil
}
// NewLock returns a handle to a lock struct which can
// be used to provide mutual exclusion on a key
func (s *Consul) NewLock(key string, options *store.LockOptions) (store.Locker, error) {
lockOpts := &api.LockOptions{
Key: s.normalize(key),
}
lock := &consulLock{}
if options != nil {
// Set optional TTL on Lock
if options.TTL != 0 {
entry := &api.SessionEntry{
Behavior: api.SessionBehaviorRelease, // Release the lock when the session expires
TTL: (options.TTL / 2).String(), // Consul multiplies the TTL by 2x
LockDelay: 1 * time.Millisecond, // Virtually disable lock delay
}
// Create the key session
session, _, err := s.client.Session().Create(entry, nil)
if err != nil {
return nil, err
}
// Place the session on lock
lockOpts.Session = session
// Renew the session ttl lock periodically
go s.client.Session().RenewPeriodic(entry.TTL, session, nil, options.RenewLock)
lock.renewCh = options.RenewLock
}
// Set optional value on Lock
if options.Value != nil {
lockOpts.Value = options.Value
}
}
l, err := s.client.LockOpts(lockOpts)
if err != nil {
return nil, err
}
lock.lock = l
return lock, nil
}
// Lock attempts to acquire the lock and blocks while
// doing so. It returns a channel that is closed if our
// lock is lost or if an error occurs
func (l *consulLock) Lock(stopChan chan struct{}) (<-chan struct{}, error) {
return l.lock.Lock(stopChan)
}
// Unlock the "key". Calling unlock while
// not holding the lock will throw an error
func (l *consulLock) Unlock() error {
if l.renewCh != nil {
close(l.renewCh)
}
return l.lock.Unlock()
}
// AtomicPut put a value at "key" if the key has not been
// modified in the meantime, throws an error if this is the case
func (s *Consul) AtomicPut(key string, value []byte, previous *store.KVPair, options *store.WriteOptions) (bool, *store.KVPair, error) {
p := &api.KVPair{Key: s.normalize(key), Value: value}
if previous == nil {
// Consul interprets ModifyIndex = 0 as new key.
p.ModifyIndex = 0
} else {
p.ModifyIndex = previous.LastIndex
}
if work, _, err := s.client.KV().CAS(p, nil); err != nil {
return false, nil, err
} else if !work {
return false, nil, store.ErrKeyModified
}
pair, err := s.Get(key)
if err != nil {
return false, nil, err
}
return true, pair, nil
}
// AtomicDelete deletes a value at "key" if the key has not
// been modified in the meantime, throws an error if this is the case
func (s *Consul) AtomicDelete(key string, previous *store.KVPair) (bool, error) {
if previous == nil {
return false, store.ErrPreviousNotSpecified
}
p := &api.KVPair{Key: s.normalize(key), ModifyIndex: previous.LastIndex}
// Extra Get operation to check on the key
_, err := s.Get(key)
if err != nil && err == store.ErrKeyNotFound {
return false, err
}
if work, _, err := s.client.KV().DeleteCAS(p, nil); err != nil {
return false, err
} else if !work {
return false, store.ErrKeyModified
}
return true, nil
}
// Close closes the client connection
func (s *Consul) Close() {
return
}