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() } } } // ServerForAddr returns server metadata for a server with the specified address. func (s *ServerResolverBuilder) ServerForAddr(addr string) (*metadata.Server, error) { s.lock.RLock() defer s.lock.RUnlock() for _, server := range s.servers { if server.Addr.String() == addr { return server, nil } } return nil, fmt.Errorf("failed to find Consul server for address %q", addr) } // 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 } // 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{ Addr: 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(leaderAddr string) { s.lock.Lock() defer s.lock.Unlock() s.leaderResolver.addr = leaderAddr 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 { addr string clientConn resolver.ClientConn } func (l leaderResolver) ResolveNow(resolver.ResolveNowOption) {} func (l leaderResolver) Close() {} func (l leaderResolver) updateClientConn() { if l.addr == "" || l.clientConn == nil { return } addrs := []resolver.Address{ { Addr: l.addr, Type: resolver.Backend, ServerName: "leader", }, } l.clientConn.UpdateState(resolver.State{Addresses: addrs}) } var _ resolver.Resolver = (*leaderResolver)(nil)