summaryrefslogtreecommitdiff
path: root/vendor/google.golang.org/grpc/balancer/balancer.go
blob: 178de0898aa4a4a76450e313e5647762ad8c48a4 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
/*
 *
 * Copyright 2017 gRPC authors.
 *
 * 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 balancer defines APIs for load balancing in gRPC.
// All APIs in this package are experimental.
package balancer

import (
	"context"
	"encoding/json"
	"errors"
	"net"
	"strings"

	"google.golang.org/grpc/connectivity"
	"google.golang.org/grpc/credentials"
	"google.golang.org/grpc/internal"
	"google.golang.org/grpc/metadata"
	"google.golang.org/grpc/resolver"
	"google.golang.org/grpc/serviceconfig"
)

var (
	// m is a map from name to balancer builder.
	m = make(map[string]Builder)
)

// Register registers the balancer builder to the balancer map. b.Name
// (lowercased) will be used as the name registered with this builder.  If the
// Builder implements ConfigParser, ParseConfig will be called when new service
// configs are received by the resolver, and the result will be provided to the
// Balancer in UpdateClientConnState.
//
// NOTE: this function must only be called during initialization time (i.e. in
// an init() function), and is not thread-safe. If multiple Balancers are
// registered with the same name, the one registered last will take effect.
func Register(b Builder) {
	m[strings.ToLower(b.Name())] = b
}

// unregisterForTesting deletes the balancer with the given name from the
// balancer map.
//
// This function is not thread-safe.
func unregisterForTesting(name string) {
	delete(m, name)
}

func init() {
	internal.BalancerUnregister = unregisterForTesting
}

// Get returns the resolver builder registered with the given name.
// Note that the compare is done in a case-insensitive fashion.
// If no builder is register with the name, nil will be returned.
func Get(name string) Builder {
	if b, ok := m[strings.ToLower(name)]; ok {
		return b
	}
	return nil
}

// A SubConn represents a single connection to a gRPC backend service.
//
// Each SubConn contains a list of addresses.
//
// All SubConns start in IDLE, and will not try to connect. To trigger the
// connecting, Balancers must call Connect.  If a connection re-enters IDLE,
// Balancers must call Connect again to trigger a new connection attempt.
//
// gRPC will try to connect to the addresses in sequence, and stop trying the
// remainder once the first connection is successful. If an attempt to connect
// to all addresses encounters an error, the SubConn will enter
// TRANSIENT_FAILURE for a backoff period, and then transition to IDLE.
//
// Once established, if a connection is lost, the SubConn will transition
// directly to IDLE.
//
// This interface is to be implemented by gRPC. Users should not need their own
// implementation of this interface. For situations like testing, any
// implementations should embed this interface. This allows gRPC to add new
// methods to this interface.
type SubConn interface {
	// UpdateAddresses updates the addresses used in this SubConn.
	// gRPC checks if currently-connected address is still in the new list.
	// If it's in the list, the connection will be kept.
	// If it's not in the list, the connection will gracefully closed, and
	// a new connection will be created.
	//
	// This will trigger a state transition for the SubConn.
	//
	// Deprecated: This method is now part of the ClientConn interface and will
	// eventually be removed from here.
	UpdateAddresses([]resolver.Address)
	// Connect starts the connecting for this SubConn.
	Connect()
}

// NewSubConnOptions contains options to create new SubConn.
type NewSubConnOptions struct {
	// CredsBundle is the credentials bundle that will be used in the created
	// SubConn. If it's nil, the original creds from grpc DialOptions will be
	// used.
	//
	// Deprecated: Use the Attributes field in resolver.Address to pass
	// arbitrary data to the credential handshaker.
	CredsBundle credentials.Bundle
	// HealthCheckEnabled indicates whether health check service should be
	// enabled on this SubConn
	HealthCheckEnabled bool
}

// State contains the balancer's state relevant to the gRPC ClientConn.
type State struct {
	// State contains the connectivity state of the balancer, which is used to
	// determine the state of the ClientConn.
	ConnectivityState connectivity.State
	// Picker is used to choose connections (SubConns) for RPCs.
	Picker Picker
}

// ClientConn represents a gRPC ClientConn.
//
// This interface is to be implemented by gRPC. Users should not need a
// brand new implementation of this interface. For the situations like
// testing, the new implementation should embed this interface. This allows
// gRPC to add new methods to this interface.
type ClientConn interface {
	// NewSubConn is called by balancer to create a new SubConn.
	// It doesn't block and wait for the connections to be established.
	// Behaviors of the SubConn can be controlled by options.
	NewSubConn([]resolver.Address, NewSubConnOptions) (SubConn, error)
	// RemoveSubConn removes the SubConn from ClientConn.
	// The SubConn will be shutdown.
	RemoveSubConn(SubConn)
	// UpdateAddresses updates the addresses used in the passed in SubConn.
	// gRPC checks if the currently connected address is still in the new list.
	// If so, the connection will be kept. Else, the connection will be
	// gracefully closed, and a new connection will be created.
	//
	// This will trigger a state transition for the SubConn.
	UpdateAddresses(SubConn, []resolver.Address)

	// UpdateState notifies gRPC that the balancer's internal state has
	// changed.
	//
	// gRPC will update the connectivity state of the ClientConn, and will call
	// Pick on the new Picker to pick new SubConns.
	UpdateState(State)

	// ResolveNow is called by balancer to notify gRPC to do a name resolving.
	ResolveNow(resolver.ResolveNowOptions)

	// Target returns the dial target for this ClientConn.
	//
	// Deprecated: Use the Target field in the BuildOptions instead.
	Target() string
}

// BuildOptions contains additional information for Build.
type BuildOptions struct {
	// DialCreds is the transport credential the Balancer implementation can
	// use to dial to a remote load balancer server. The Balancer implementations
	// can ignore this if it does not need to talk to another party securely.
	DialCreds credentials.TransportCredentials
	// CredsBundle is the credentials bundle that the Balancer can use.
	CredsBundle credentials.Bundle
	// Dialer is the custom dialer the Balancer implementation can use to dial
	// to a remote load balancer server. The Balancer implementations
	// can ignore this if it doesn't need to talk to remote balancer.
	Dialer func(context.Context, string) (net.Conn, error)
	// ChannelzParentID is the entity parent's channelz unique identification number.
	ChannelzParentID int64
	// CustomUserAgent is the custom user agent set on the parent ClientConn.
	// The balancer should set the same custom user agent if it creates a
	// ClientConn.
	CustomUserAgent string
	// Target contains the parsed address info of the dial target. It is the same resolver.Target as
	// passed to the resolver.
	// See the documentation for the resolver.Target type for details about what it contains.
	Target resolver.Target
}

// Builder creates a balancer.
type Builder interface {
	// Build creates a new balancer with the ClientConn.
	Build(cc ClientConn, opts BuildOptions) Balancer
	// Name returns the name of balancers built by this builder.
	// It will be used to pick balancers (for example in service config).
	Name() string
}

// ConfigParser parses load balancer configs.
type ConfigParser interface {
	// ParseConfig parses the JSON load balancer config provided into an
	// internal form or returns an error if the config is invalid.  For future
	// compatibility reasons, unknown fields in the config should be ignored.
	ParseConfig(LoadBalancingConfigJSON json.RawMessage) (serviceconfig.LoadBalancingConfig, error)
}

// PickInfo contains additional information for the Pick operation.
type PickInfo struct {
	// FullMethodName is the method name that NewClientStream() is called
	// with. The canonical format is /service/Method.
	FullMethodName string
	// Ctx is the RPC's context, and may contain relevant RPC-level information
	// like the outgoing header metadata.
	Ctx context.Context
}

// DoneInfo contains additional information for done.
type DoneInfo struct {
	// Err is the rpc error the RPC finished with. It could be nil.
	Err error
	// Trailer contains the metadata from the RPC's trailer, if present.
	Trailer metadata.MD
	// BytesSent indicates if any bytes have been sent to the server.
	BytesSent bool
	// BytesReceived indicates if any byte has been received from the server.
	BytesReceived bool
	// ServerLoad is the load received from server. It's usually sent as part of
	// trailing metadata.
	//
	// The only supported type now is *orca_v1.LoadReport.
	ServerLoad interface{}
}

var (
	// ErrNoSubConnAvailable indicates no SubConn is available for pick().
	// gRPC will block the RPC until a new picker is available via UpdateState().
	ErrNoSubConnAvailable = errors.New("no SubConn is available")
	// ErrTransientFailure indicates all SubConns are in TransientFailure.
	// WaitForReady RPCs will block, non-WaitForReady RPCs will fail.
	//
	// Deprecated: return an appropriate error based on the last resolution or
	// connection attempt instead.  The behavior is the same for any non-gRPC
	// status error.
	ErrTransientFailure = errors.New("all SubConns are in TransientFailure")
)

// PickResult contains information related to a connection chosen for an RPC.
type PickResult struct {
	// SubConn is the connection to use for this pick, if its state is Ready.
	// If the state is not Ready, gRPC will block the RPC until a new Picker is
	// provided by the balancer (using ClientConn.UpdateState).  The SubConn
	// must be one returned by ClientConn.NewSubConn.
	SubConn SubConn

	// Done is called when the RPC is completed.  If the SubConn is not ready,
	// this will be called with a nil parameter.  If the SubConn is not a valid
	// type, Done may not be called.  May be nil if the balancer does not wish
	// to be notified when the RPC completes.
	Done func(DoneInfo)
}

// TransientFailureError returns e.  It exists for backward compatibility and
// will be deleted soon.
//
// Deprecated: no longer necessary, picker errors are treated this way by
// default.
func TransientFailureError(e error) error { return e }

// Picker is used by gRPC to pick a SubConn to send an RPC.
// Balancer is expected to generate a new picker from its snapshot every time its
// internal state has changed.
//
// The pickers used by gRPC can be updated by ClientConn.UpdateState().
type Picker interface {
	// Pick returns the connection to use for this RPC and related information.
	//
	// Pick should not block.  If the balancer needs to do I/O or any blocking
	// or time-consuming work to service this call, it should return
	// ErrNoSubConnAvailable, and the Pick call will be repeated by gRPC when
	// the Picker is updated (using ClientConn.UpdateState).
	//
	// If an error is returned:
	//
	// - If the error is ErrNoSubConnAvailable, gRPC will block until a new
	//   Picker is provided by the balancer (using ClientConn.UpdateState).
	//
	// - If the error is a status error (implemented by the grpc/status
	//   package), gRPC will terminate the RPC with the code and message
	//   provided.
	//
	// - For all other errors, wait for ready RPCs will wait, but non-wait for
	//   ready RPCs will be terminated with this error's Error() string and
	//   status code Unavailable.
	Pick(info PickInfo) (PickResult, error)
}

// Balancer takes input from gRPC, manages SubConns, and collects and aggregates
// the connectivity states.
//
// It also generates and updates the Picker used by gRPC to pick SubConns for RPCs.
//
// UpdateClientConnState, ResolverError, UpdateSubConnState, and Close are
// guaranteed to be called synchronously from the same goroutine.  There's no
// guarantee on picker.Pick, it may be called anytime.
type Balancer interface {
	// UpdateClientConnState is called by gRPC when the state of the ClientConn
	// changes.  If the error returned is ErrBadResolverState, the ClientConn
	// will begin calling ResolveNow on the active name resolver with
	// exponential backoff until a subsequent call to UpdateClientConnState
	// returns a nil error.  Any other errors are currently ignored.
	UpdateClientConnState(ClientConnState) error
	// ResolverError is called by gRPC when the name resolver reports an error.
	ResolverError(error)
	// UpdateSubConnState is called by gRPC when the state of a SubConn
	// changes.
	UpdateSubConnState(SubConn, SubConnState)
	// Close closes the balancer. The balancer is not required to call
	// ClientConn.RemoveSubConn for its existing SubConns.
	Close()
}

// ExitIdler is an optional interface for balancers to implement.  If
// implemented, ExitIdle will be called when ClientConn.Connect is called, if
// the ClientConn is idle.  If unimplemented, ClientConn.Connect will cause
// all SubConns to connect.
//
// Notice: it will be required for all balancers to implement this in a future
// release.
type ExitIdler interface {
	// ExitIdle instructs the LB policy to reconnect to backends / exit the
	// IDLE state, if appropriate and possible.  Note that SubConns that enter
	// the IDLE state will not reconnect until SubConn.Connect is called.
	ExitIdle()
}

// SubConnState describes the state of a SubConn.
type SubConnState struct {
	// ConnectivityState is the connectivity state of the SubConn.
	ConnectivityState connectivity.State
	// ConnectionError is set if the ConnectivityState is TransientFailure,
	// describing the reason the SubConn failed.  Otherwise, it is nil.
	ConnectionError error
}

// ClientConnState describes the state of a ClientConn relevant to the
// balancer.
type ClientConnState struct {
	ResolverState resolver.State
	// The parsed load balancing configuration returned by the builder's
	// ParseConfig method, if implemented.
	BalancerConfig serviceconfig.LoadBalancingConfig
}

// ErrBadResolverState may be returned by UpdateClientConnState to indicate a
// problem with the provided name resolver data.
var ErrBadResolverState = errors.New("bad resolver state")

// ConnectivityStateEvaluator takes the connectivity states of multiple SubConns
// and returns one aggregated connectivity state.
//
// It's not thread safe.
type ConnectivityStateEvaluator struct {
	numReady            uint64 // Number of addrConns in ready state.
	numConnecting       uint64 // Number of addrConns in connecting state.
	numTransientFailure uint64 // Number of addrConns in transient failure state.
	numIdle             uint64 // Number of addrConns in idle state.
}

// RecordTransition records state change happening in subConn and based on that
// it evaluates what aggregated state should be.
//
//  - If at least one SubConn in Ready, the aggregated state is Ready;
//  - Else if at least one SubConn in Connecting, the aggregated state is Connecting;
//  - Else if at least one SubConn is TransientFailure, the aggregated state is Transient Failure;
//  - Else if at least one SubConn is Idle, the aggregated state is Idle;
//  - Else there are no subconns and the aggregated state is Transient Failure
//
// Shutdown is not considered.
func (cse *ConnectivityStateEvaluator) RecordTransition(oldState, newState connectivity.State) connectivity.State {
	// Update counters.
	for idx, state := range []connectivity.State{oldState, newState} {
		updateVal := 2*uint64(idx) - 1 // -1 for oldState and +1 for new.
		switch state {
		case connectivity.Ready:
			cse.numReady += updateVal
		case connectivity.Connecting:
			cse.numConnecting += updateVal
		case connectivity.TransientFailure:
			cse.numTransientFailure += updateVal
		case connectivity.Idle:
			cse.numIdle += updateVal
		}
	}

	// Evaluate.
	if cse.numReady > 0 {
		return connectivity.Ready
	}
	if cse.numConnecting > 0 {
		return connectivity.Connecting
	}
	if cse.numTransientFailure > 0 {
		return connectivity.TransientFailure
	}
	if cse.numIdle > 0 {
		return connectivity.Idle
	}
	return connectivity.TransientFailure
}