open-consul/agent/grpc/resolver/resolver.go

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package resolver
import (
"fmt"
"math/rand"
"strings"
"sync"
"time"
"google.golang.org/grpc/resolver"
"github.com/hashicorp/consul/agent/metadata"
)
// ServerResolverBuilder tracks the current server list and keeps any
// ServerResolvers updated when changes occur.
type ServerResolverBuilder struct {
cfg Config
// leaderResolver is used to track the address of the leader in the local DC.
leaderResolver leaderResolver
// servers is an index of Servers by Server.ID. The map contains server IDs
// for all datacenters.
servers map[string]*metadata.Server
// resolvers is an index of connections to the serverResolver which manages
// addresses of servers for that connection.
resolvers map[resolver.ClientConn]*serverResolver
// lock for all stateful fields (excludes config which is immutable).
lock sync.RWMutex
}
type Config struct {
// Authority used to query the server. Defaults to "". Used to support
// parallel testing because gRPC registers resolvers globally.
Authority string
}
func NewServerResolverBuilder(cfg Config) *ServerResolverBuilder {
return &ServerResolverBuilder{
cfg: cfg,
servers: make(map[string]*metadata.Server),
resolvers: make(map[resolver.ClientConn]*serverResolver),
}
}
// NewRebalancer returns a function which shuffles the server list for resolvers
// in all datacenters.
func (s *ServerResolverBuilder) NewRebalancer(dc string) func() {
shuffler := rand.New(rand.NewSource(time.Now().UnixNano()))
return func() {
s.lock.RLock()
defer s.lock.RUnlock()
for _, resolver := range s.resolvers {
if resolver.datacenter != dc {
continue
}
// Shuffle the list of addresses using the last list given to the resolver.
resolver.addrLock.Lock()
addrs := resolver.addrs
shuffler.Shuffle(len(addrs), func(i, j int) {
addrs[i], addrs[j] = addrs[j], addrs[i]
})
// Pass the shuffled list to the resolver.
resolver.updateAddrsLocked(addrs)
resolver.addrLock.Unlock()
}
}
}
// ServerForGlobalAddr returns server metadata for a server with the specified globally unique address.
func (s *ServerResolverBuilder) ServerForGlobalAddr(globalAddr string) (*metadata.Server, error) {
s.lock.RLock()
defer s.lock.RUnlock()
for _, server := range s.servers {
if DCPrefix(server.Datacenter, server.Addr.String()) == globalAddr {
return server, nil
}
}
return nil, fmt.Errorf("failed to find Consul server for global address %q", globalAddr)
}
// Build returns a new serverResolver for the given ClientConn. The resolver
// will keep the ClientConn's state updated based on updates from Serf.
func (s *ServerResolverBuilder) Build(target resolver.Target, cc resolver.ClientConn, _ resolver.BuildOption) (resolver.Resolver, error) {
s.lock.Lock()
defer s.lock.Unlock()
// If there's already a resolver for this connection, return it.
// TODO(streaming): how would this happen since we already cache connections in ClientConnPool?
if resolver, ok := s.resolvers[cc]; ok {
return resolver, nil
}
if cc == s.leaderResolver.clientConn {
return s.leaderResolver, nil
}
serverType, datacenter, err := parseEndpoint(target.Endpoint)
if err != nil {
return nil, err
}
if serverType == "leader" {
// TODO: is this safe? can we ever have multiple CC for the leader? Seems
// like we can only have one given the caching in ClientConnPool.Dial
s.leaderResolver.clientConn = cc
s.leaderResolver.updateClientConn()
return s.leaderResolver, nil
}
// Make a new resolver for the dc and add it to the list of active ones.
resolver := &serverResolver{
datacenter: datacenter,
clientConn: cc,
close: func() {
s.lock.Lock()
defer s.lock.Unlock()
delete(s.resolvers, cc)
},
}
resolver.updateAddrs(s.getDCAddrs(datacenter))
s.resolvers[cc] = resolver
return resolver, nil
}
// parseEndpoint parses a string, expecting a format of "serverType.datacenter"
func parseEndpoint(target string) (string, string, error) {
parts := strings.SplitN(target, ".", 2)
if len(parts) != 2 {
return "", "", fmt.Errorf("unexpected endpoint address: %v", target)
}
return parts[0], parts[1], nil
}
func (s *ServerResolverBuilder) Authority() string {
return s.cfg.Authority
}
// AddServer updates the resolvers' states to include the new server's address.
func (s *ServerResolverBuilder) AddServer(server *metadata.Server) {
s.lock.Lock()
defer s.lock.Unlock()
s.servers[uniqueID(server)] = server
addrs := s.getDCAddrs(server.Datacenter)
for _, resolver := range s.resolvers {
if resolver.datacenter == server.Datacenter {
resolver.updateAddrs(addrs)
}
}
}
// uniqueID returns a unique identifier for the server which includes the
// Datacenter and the ID.
//
// In practice it is expected that the server.ID is already a globally unique
// UUID. This function is an extra safeguard in case that ever changes.
func uniqueID(server *metadata.Server) string {
return server.Datacenter + "-" + server.ID
}
// DCPrefix prefixes the given string with a datacenter for use in
// disambiguation.
func DCPrefix(datacenter, suffix string) string {
return datacenter + "-" + suffix
}
// RemoveServer updates the resolvers' states with the given server removed.
func (s *ServerResolverBuilder) RemoveServer(server *metadata.Server) {
s.lock.Lock()
defer s.lock.Unlock()
delete(s.servers, uniqueID(server))
addrs := s.getDCAddrs(server.Datacenter)
for _, resolver := range s.resolvers {
if resolver.datacenter == server.Datacenter {
resolver.updateAddrs(addrs)
}
}
}
// getDCAddrs returns a list of the server addresses for the given datacenter.
// This method requires that lock is held for reads.
func (s *ServerResolverBuilder) getDCAddrs(dc string) []resolver.Address {
var addrs []resolver.Address
for _, server := range s.servers {
if server.Datacenter != dc {
continue
}
addrs = append(addrs, resolver.Address{
// NOTE: the address persisted here is only dialable using our custom dialer
Addr: DCPrefix(server.Datacenter, server.Addr.String()),
Type: resolver.Backend,
ServerName: server.Name,
})
}
return addrs
}
// UpdateLeaderAddr updates the leader address in the local DC's resolver.
func (s *ServerResolverBuilder) UpdateLeaderAddr(datacenter, addr string) {
s.lock.Lock()
defer s.lock.Unlock()
s.leaderResolver.globalAddr = DCPrefix(datacenter, addr)
s.leaderResolver.updateClientConn()
}
// serverResolver is a grpc Resolver that will keep a grpc.ClientConn up to date
// on the list of server addresses to use.
type serverResolver struct {
// datacenter that can be reached by the clientConn. Used by ServerResolverBuilder
// to filter resolvers for those in a specific datacenter.
datacenter string
// clientConn that this resolver is providing addresses for.
clientConn resolver.ClientConn
// close is used by ServerResolverBuilder to remove this resolver from the
// index of resolvers. It is called by grpc when the connection is closed.
close func()
// addrs stores the list of addresses passed to updateAddrs, so that they
// can be rebalanced periodically by ServerResolverBuilder.
addrs []resolver.Address
addrLock sync.Mutex
}
var _ resolver.Resolver = (*serverResolver)(nil)
// updateAddrs updates this serverResolver's ClientConn to use the given set of
// addrs.
func (r *serverResolver) updateAddrs(addrs []resolver.Address) {
r.addrLock.Lock()
defer r.addrLock.Unlock()
r.updateAddrsLocked(addrs)
}
// updateAddrsLocked updates this serverResolver's ClientConn to use the given
// set of addrs. addrLock must be held by caller.
func (r *serverResolver) updateAddrsLocked(addrs []resolver.Address) {
// Only pass the first address initially, which will cause the
// balancer to spin down the connection for its previous first address
// if it is different. If we don't do this, it will keep using the old
// first address as long as it is still in the list, making it impossible to
// rebalance until that address is removed.
var firstAddr []resolver.Address
if len(addrs) > 0 {
firstAddr = []resolver.Address{addrs[0]}
}
r.clientConn.UpdateState(resolver.State{Addresses: firstAddr})
// Call UpdateState again with the entire list of addrs in case we need them
// for failover.
r.clientConn.UpdateState(resolver.State{Addresses: addrs})
r.addrs = addrs
}
func (r *serverResolver) Close() {
r.close()
}
// ResolveNow is not used
func (*serverResolver) ResolveNow(resolver.ResolveNowOption) {}
type leaderResolver struct {
globalAddr string
clientConn resolver.ClientConn
}
func (l leaderResolver) ResolveNow(resolver.ResolveNowOption) {}
func (l leaderResolver) Close() {}
func (l leaderResolver) updateClientConn() {
if l.globalAddr == "" || l.clientConn == nil {
return
}
addrs := []resolver.Address{
{
// NOTE: the address persisted here is only dialable using our custom dialer
Addr: l.globalAddr,
Type: resolver.Backend,
ServerName: "leader",
},
}
l.clientConn.UpdateState(resolver.State{Addresses: addrs})
}
var _ resolver.Resolver = (*leaderResolver)(nil)