package grpc import ( "context" "fmt" "net" "sync" "time" "google.golang.org/grpc" "google.golang.org/grpc/keepalive" "github.com/hashicorp/consul/agent/metadata" "github.com/hashicorp/consul/agent/pool" ) // ClientConnPool creates and stores a connection for each datacenter. type ClientConnPool struct { dialer dialer servers ServerLocator conns map[string]*grpc.ClientConn connsLock sync.Mutex } type ServerLocator interface { // ServerForAddr is used to look up server metadata from an address. ServerForAddr(addr string) (*metadata.Server, error) // Authority returns the target authority to use to dial the server. This is primarily // needed for testing multiple agents in parallel, because gRPC requires the // resolver to be registered globally. Authority() string } // TLSWrapper wraps a non-TLS connection and returns a connection with TLS // enabled. type TLSWrapper func(dc string, conn net.Conn) (net.Conn, error) type dialer func(context.Context, string) (net.Conn, error) // NewClientConnPool create new GRPC client pool to connect to servers using GRPC over RPC func NewClientConnPool(servers ServerLocator, tls TLSWrapper, useTLSForDC func(dc string) bool) *ClientConnPool { return &ClientConnPool{ dialer: newDialer(servers, tls, useTLSForDC), servers: servers, conns: make(map[string]*grpc.ClientConn), } } // ClientConn returns a grpc.ClientConn for the datacenter. If there are no // existing connections in the pool, a new one will be created, stored in the pool, // then returned. func (c *ClientConnPool) ClientConn(datacenter string) (*grpc.ClientConn, error) { c.connsLock.Lock() defer c.connsLock.Unlock() if conn, ok := c.conns[datacenter]; ok { return conn, nil } conn, err := grpc.Dial( fmt.Sprintf("consul://%s/server.%s", c.servers.Authority(), datacenter), // use WithInsecure mode here because we handle the TLS wrapping in the // custom dialer based on logic around whether the server has TLS enabled. grpc.WithInsecure(), grpc.WithContextDialer(c.dialer), grpc.WithDisableRetry(), grpc.WithStatsHandler(newStatsHandler(defaultMetrics())), // nolint:staticcheck // there is no other supported alternative to WithBalancerName grpc.WithBalancerName("pick_first"), // Keep alive parameters are based on the same default ones we used for // Yamux. These are somewhat arbitrary but we did observe in scale testing // that the gRPC defaults (servers send keepalives only every 2 hours, // clients never) seemed to result in TCP drops going undetected until // actual updates needed to be sent which caused unnecessary delays for // deliveries. These settings should be no more work for servers than // existing yamux clients but hopefully allow TCP drops to be detected // earlier and so have a smaller chance of going unnoticed until there are // actual updates to send out from the servers. The servers have a policy to // not accept pings any faster than once every 15 seconds to protect against // abuse. grpc.WithKeepaliveParams(keepalive.ClientParameters{ Time: 30 * time.Second, Timeout: 10 * time.Second, })) if err != nil { return nil, err } c.conns[datacenter] = conn return conn, nil } // newDialer returns a gRPC dialer function that conditionally wraps the connection // with TLS based on the Server.useTLS value. func newDialer(servers ServerLocator, wrapper TLSWrapper, useTLSForDC func(dc string) bool) func(context.Context, string) (net.Conn, error) { return func(ctx context.Context, addr string) (net.Conn, error) { d := net.Dialer{} conn, err := d.DialContext(ctx, "tcp", addr) if err != nil { return nil, err } server, err := servers.ServerForAddr(addr) if err != nil { conn.Close() return nil, err } if server.UseTLS && useTLSForDC(server.Datacenter) { if wrapper == nil { conn.Close() return nil, fmt.Errorf("TLS enabled but got nil TLS wrapper") } // Switch the connection into TLS mode if _, err := conn.Write([]byte{byte(pool.RPCTLS)}); err != nil { conn.Close() return nil, err } // Wrap the connection in a TLS client tlsConn, err := wrapper(server.Datacenter, conn) if err != nil { conn.Close() return nil, err } conn = tlsConn } _, err = conn.Write([]byte{pool.RPCGRPC}) if err != nil { conn.Close() return nil, err } return conn, nil } }