open-consul/agent/grpc/client.go

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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)
// Scheme returns the url scheme 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.
Scheme() 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("%s:///server.%s", c.servers.Scheme(), 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
}
}