go.etcd.io/etcd@v3.3.27+incompatible/clientv3/balancer/picker/picker.go (about)

     1  // Copyright 2018 The etcd Authors
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package picker
    16  
    17  import (
    18  	"fmt"
    19  
    20  	"go.uber.org/zap"
    21  	"google.golang.org/grpc/balancer"
    22  	"google.golang.org/grpc/resolver"
    23  )
    24  
    25  // Picker defines balancer Picker methods.
    26  type Picker interface {
    27  	balancer.Picker
    28  	String() string
    29  }
    30  
    31  // Config defines picker configuration.
    32  type Config struct {
    33  	// Policy specifies etcd clientv3's built in balancer policy.
    34  	Policy Policy
    35  
    36  	// Logger defines picker logging object.
    37  	Logger *zap.Logger
    38  
    39  	// SubConnToResolverAddress maps each gRPC sub-connection to an address.
    40  	// Basically, it is a list of addresses that the Picker can pick from.
    41  	SubConnToResolverAddress map[balancer.SubConn]resolver.Address
    42  }
    43  
    44  // Policy defines balancer picker policy.
    45  type Policy uint8
    46  
    47  const (
    48  	// Error is error picker policy.
    49  	Error Policy = iota
    50  
    51  	// RoundrobinBalanced balances loads over multiple endpoints
    52  	// and implements failover in roundrobin fashion.
    53  	RoundrobinBalanced
    54  
    55  	// Custom defines custom balancer picker.
    56  	// TODO: custom picker is not supported yet.
    57  	Custom
    58  )
    59  
    60  func (p Policy) String() string {
    61  	switch p {
    62  	case Error:
    63  		return "picker-error"
    64  
    65  	case RoundrobinBalanced:
    66  		return "picker-roundrobin-balanced"
    67  
    68  	case Custom:
    69  		panic("'custom' picker policy is not supported yet")
    70  
    71  	default:
    72  		panic(fmt.Errorf("invalid balancer picker policy (%d)", p))
    73  	}
    74  }
    75  
    76  // New creates a new Picker.
    77  func New(cfg Config) Picker {
    78  	switch cfg.Policy {
    79  	case Error:
    80  		panic("'error' picker policy is not supported here; use 'picker.NewErr'")
    81  
    82  	case RoundrobinBalanced:
    83  		return newRoundrobinBalanced(cfg)
    84  
    85  	case Custom:
    86  		panic("'custom' picker policy is not supported yet")
    87  
    88  	default:
    89  		panic(fmt.Errorf("invalid balancer picker policy (%d)", cfg.Policy))
    90  	}
    91  }