用etcd做go-micro的服务发现

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来源：池塘边的卡夫卡

https://zhuanlan.zhihu.com/p/79897640

【导读】做微服务架构，微服务的治理统一框架其实非常有必要。本文介绍了如何使用golang和etcd实现服务发现。

在golang的生态中有众多框架，比如go-micro和go-kit还有华为开源的ServiceComb。

go-micro提供了一系列的组件，隐藏了分布式系统的复杂性，并为开发人员提供了很好的理解概念。开发者在开发的时候选择自己的组件就好了，如果系统不能支持，可以很方便的扩展。

在使用go-micro的服务发现组件的时候，由于我个人非常喜欢etcd。并且在一些分布式系统中可能会使用到分布式锁，所以服务发现的驱动我首选etcd。go-micro为etcd提供两组api一组是etcd一组是etcdv3。抱着用新不用久的思想果断选择etcdv3，这时候发现其实有一些坑。

按照官方文档我们的驱动选择etcd。代码如下

registerDrive := etcdv3.NewRegistry(func(op *registry.Options) {
    op.Addrs = []string{
        "http://127.0.0.1:2379",
    }
})

service := micro.NewService(
        micro.Transport(tg.NewTransport()),
        micro.Server(grpc.NewServer()),
        micro.Registry(registerDrive),
        micro.Broker(brokerDrive),
        micro.Name("userSrv"),
        micro.Version("latest"),
)

然后我们启动etcd，启动etcd这时候发现报错。

../../../../github.com/coreos/etcd/clientv3/auth.go:121:72: cannot use auth.callOpts (type []"github.com/coreos/etcd/vendor/google.golang.org/grpc".CallOption) as type []"vendor/google.golang.org/grpc".CallOption in argument to auth.remote.AuthEnable
../../../../github.com/coreos/etcd/clientv3/auth.go:126:74: cannot use auth.callOpts (type []"github.com/coreos/etcd/vendor/google.golang.org/grpc".CallOption) as type []"vendor/google.golang.org/grpc".CallOption in argument to auth.remote.AuthDisable
../../../../github.com/coreos/etcd/clientv3/auth.go:131:152: cannot use auth.callOpts (type []"github.com/coreos/etcd/vendor/google.golang.org/grpc".CallOption) as type []"vendor/google.golang.org/grpc".CallOption in argument to auth.remote.UserAdd
../../../../github.com/coreos/etcd/clientv3/auth.go:136:144: cannot use auth.callOpts (type []"github.com/coreos/etcd/vendor/google.golang.org/grpc".CallOption) as type []"vendor/google.golang.org/grpc".CallOption in argument to auth.remote.UserAdd
../../../../github.com/coreos/etcd/clientv3/auth.go:141:86: cannot use auth.callOpts (type []"github.com/coreos/etcd/vendor/google.golang.org/grpc".CallOption) as type []"vendor/google.golang.org/grpc".CallOption in argument to auth.remote.UserDelete
../../../../github.com/coreos/etcd/clientv3/auth.go:146:122: cannot use auth.callOpts (type []"github.com/coreos/etcd/vendor/google.golang.org/grpc".CallOption) as type []"vendor/google.golang.org/grpc".CallOption in argument to auth.remote.UserChangePassword
../../../../github.com/coreos/etcd/clientv3/auth.go:151:104: cannot use auth.callOpts (type []"github.com/coreos/etcd/vendor/google.golang.org/grpc".CallOption) as type []"vendor/google.golang.org/grpc".CallOption in argument to auth.remote.UserGrantRole
../../../../github.com/coreos/etcd/clientv3/auth.go:156:80: cannot use auth.callOpts (type []"github.com/coreos/etcd/vendor/google.golang.org/grpc".CallOption) as type []"vendor/google.golang.org/grpc".CallOption in argument to auth.remote.UserGet
../../../../github.com/coreos/etcd/clientv3/auth.go:161:72: cannot use auth.callOpts (type []"github.com/coreos/etcd/vendor/google.golang.org/grpc".CallOption) as type []"vendor/google.golang.org/grpc".CallOption in argument to auth.remote.UserList
../../../../github.com/coreos/etcd/clientv3/auth.go:166:106: cannot use auth.callOpts (type []"github.com/coreos/etcd/vendor/google.golang.org/grpc".CallOption) as type []"vendor/google.golang.org/grpc".CallOption in argument to auth.remote.UserRevokeRole
../../../../github.com/coreos/etcd/clientv3/auth.go:166:106: too many errors

这时候我们谷歌一下，查查到底为啥报错。发现在etcd的github里面有一条issues。https://link.zhihu.com/?target=https%3A//github.com/etcd-io/etcd/issues/10051‍

这时候我们就清楚什么原因了，在go-micro里面引用的etcd的包是 github.com/coreos/etcd/而不是go.etcd.io/etcd/clientv这样一来可能就需要改源码了。

找到包github.com/micro/go-plu下发现三个文件一个个改掉就好

//watcher.go
import (
    "context"
    "errors"
    "time"

    //"github.com/coreos/etcd/clientv3"
    
    "go.etcd.io/etcd/clientv3"
    
    "github.com/micro/go-micro/registry"
)

//etcdv3.go
import (
    "context"
    "crypto/tls"
    "encoding/json"
    "errors"
    "path"
    "strings"
    "sync"
    "time"

    //"github.com/coreos/etcd/clientv3"

    "go.etcd.io/etcd/clientv3"  // 新加

    "github.com/micro/go-micro/config/cmd"
    "github.com/micro/go-micro/registry"

    //"github.com/coreos/etcd/etcdserver/api/v3rpc/rpctypes"

    "go.etcd.io/etcd/etcdserver/api/v3rpc/rpctypes"  // 新加

    hash "github.com/mitchellh/hashstructure"
)

改掉这些代码的时候发现etcd存进去的时候前缀我们顺便再机器上面watch一下

var (
    prefix = "/micro-registry"
)

etcdctl watch "/micro-registry" --prefix

运行代码 看看我们watch监控的结果

PUT
/micro-registry/userSrv/userSrv-4dfc1310-ba3e-4f76-a770-74ae5b4c074e
{"name":"userSrv","version":"latest","metadata":null,"endpoints":[{"name":"User.Call","request":{"name":"Request","type":"Request","values":[{"name":"name","type":"string","values":null}]},"response":{"name":"Response","type":"Response","values":[{"name":"msg","type":"string","values":null}]},"metadata":{"stream":"false"}},{"name":"User.PingPong","request":{"name":"Context","type":"Context","values":null},"response":{"name":"Stream","type":"Stream","values":null},"metadata":{"stream":"true"}},{"name":"User.Stream","request":{"name":"Context","type":"Context","values":null},"response":{"name":"Stream","type":"Stream","values":null},"metadata":{"stream":"true"}}],"nodes":[{"id":"userSrv-4dfc1310-ba3e-4f76-a770-74ae5b4c074e","address":"10.0.2.15:38068","metadata":{"broker":"rabbitmq","registry":"etcdv3","server":"grpc","transport":"grpc"}}]}

停止程序

DELETE
/micro-registry/userSrv/userSrv-4dfc1310-ba3e-4f76-a770-74ae5b4c074e

这样一来我们就可以使用etcd做服务发现了，其实关于这一块的代码也很简单，甚至你自己也可以去实现。具体可以参照他的代码，有空甚至你可以使用redis的发布订阅或者写一个基于redis驱动的练练手。

// 需要实现的接口如下
type Registry interface {
    Register(*Service, ...RegisterOption) error
    Deregister(*Service) error
    GetService(string) ([]*Service, error)
    ListServices() ([]*Service, error)
    Watch(...WatchOption) (Watcher, error)
    String() string
    Options() Options
}

另外需要删除etcd包下面的vendor文件，不然也会报错。

其他

1. 上述的容器都不是goroutines 安全的

2. 上面的lr 也不是goroutines 安全的

3. Ring 中不建议在Do 方法中修改Ring 的指针，行为是未定义的

 - EOF -

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