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derp/derpserver: implement hierarchical token bucket rate limiting

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By adding a server-global parent bucket. Per-client rate limiting is
subject to the parent bucket if global rate limiting is enabled.

This implementation is experimental, and all related APIs should be
considered unstable.

Updates tailscale/corp#40291

Signed-off-by: Jordan Whited <jordan@tailscale.com>
This commit is contained in:
Jordan Whited
2026-04-13 19:34:34 -07:00
committed by Jordan Whited
parent 5eb0b4be31
commit d8190e0de5
2 changed files with 243 additions and 152 deletions
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derp/derpserver/derpserver.go
+88 -62
View File
@@ -181,7 +181,11 @@ type Server struct {
verifyClientsURL string
verifyClientsURLFailOpen bool
mu syncs.Mutex
perClientSendQueueDepth int // Sets the client send queue depth for the server.
tcpWriteTimeout time.Duration
clock tstime.Clock
mu syncs.Mutex // guards the following fields
closed bool
netConns map[derp.Conn]chan struct{} // chan is closed when conn closes
clients map[key.NodePublic]*clientSet
@@ -197,25 +201,10 @@ type Server struct {
// is gone from the region, we notify all of these watchers,
// calling their funcs in a new goroutine.
peerGoneWatchers map[key.NodePublic]set.HandleSet[func(key.NodePublic)]
// maps from netip.AddrPort to a client's public key
keyOfAddr map[netip.AddrPort]key.NodePublic
// Sets the client send queue depth for the server.
perClientSendQueueDepth int
tcpWriteTimeout time.Duration
// perClientRecvBytesPerSec is the rate limit for receiving data from
// a single client connection, in bytes per second. 0 means unlimited.
// Mesh peers are exempt from this limit.
perClientRecvBytesPerSec uint64
// perClientRecvBurst is the burst size in bytes for the per-client
// receive rate limiter. Always at least [derp.MaxPacketSize] when
// set via [Server.UpdatePerClientRateLimit].
perClientRecvBurst uint64
clock tstime.Clock
keyOfAddr map[netip.AddrPort]key.NodePublic
rateConfig RateConfig // server-global and per-client DERP frame rate limiting config
recvLim *xrate.Limiter // server-global DERP frame receive limiter
}
// clientSet represents 1 or more *sclients.
@@ -523,16 +512,29 @@ func (s *Server) SetTCPWriteTimeout(d time.Duration) {
// our token bucket calls for.
const minRateLimitTokenBucketSize = derp.MaxPacketSize + derp.KeyLen
// RateConfig is a JSON-serializable configuration for per-client rate limits.
// Values are in bytes.
// RateConfig is a JSON-serializable configuration for rate limits. Values are
// in bytes.
type RateConfig struct {
// PerClientRateLimitBytesPerSec represents the per-client
// rate limit in bytes per second. A zero value disables rate-limiting.
// rate limit in bytes per second. A zero value disables rate limiting.
PerClientRateLimitBytesPerSec uint64 `json:",omitzero"`
// PerClientRateBurstBytes represents the per-client token bucket depth,
// or burst, in bytes. Any value lower than [minRateLimitTokenBucketSize]
// will be increased to [minRateLimitTokenBucketSize] before application.
// will be increased to [minRateLimitTokenBucketSize] before application. Only
// relevant if PerClientRateLimitBytesPerSec is nonzero.
PerClientRateBurstBytes uint64 `json:",omitzero"`
// GlobalRateLimitBytesPerSec represents the global rate limit in bytes per
// second. A zero value disables global rate limiting, but per-client (PerClient...)
// configuration may still apply. Only relevant if PerClientRateLimitBytesPerSec
// is nonzero. If GlobalRateLimitBytesPerSec is nonzero and less than
// PerClientRateLimitBytesPerSec, then GlobalRateLimitBytesPerSec will be set
// equal to PerClientRateLimitBytesPerSec before application.
GlobalRateLimitBytesPerSec uint64 `json:",omitzero"`
// GlobalRateBurstBytes represents the global token bucket depth, or burst,
// in bytes. Any value lower than [minRateLimitTokenBucketSize] will be increased to
// [minRateLimitTokenBucketSize] before application. Only relevant if
// PerClientRateLimitBytesPerSec and GlobalRateLimitBytesPerSec are nonzero.
GlobalRateBurstBytes uint64 `json:",omitzero"`
}
// LoadRateConfig reads and JSON-unmarshals a [RateConfig] from the file at path.
@@ -542,41 +544,56 @@ func LoadRateConfig(path string) (RateConfig, error) {
}
b, err := os.ReadFile(path)
if err != nil {
return RateConfig{}, fmt.Errorf("reading rate config: %w", err)
return RateConfig{}, fmt.Errorf("error reading rate config: %w", err)
}
var rc RateConfig
if err := json.Unmarshal(b, &rc); err != nil {
return RateConfig{}, fmt.Errorf("parsing rate config: %w", err)
return RateConfig{}, fmt.Errorf("error parsing rate config: %w", err)
}
return rc, nil
}
// LoadAndApplyRateConfig reads a [RateConfig] from the file at path and
// applies it to the server via [Server.UpdatePerClientRateLimit].
// applies it to the server via [Server.UpdateRateLimits].
func (s *Server) LoadAndApplyRateConfig(path string) error {
rc, err := LoadRateConfig(path)
if err != nil {
return err
}
s.UpdatePerClientRateLimit(rc.PerClientRateLimitBytesPerSec, rc.PerClientRateBurstBytes)
s.logf("rate config applied: rate=%d bytes/sec, burst=%d bytes", rc.PerClientRateLimitBytesPerSec, rc.PerClientRateBurstBytes)
applied := s.UpdateRateLimits(rc)
s.logf("rate config applied: global-rate=%d bytes/sec global-burst=%d bytes client-rate=%d bytes/sec, client-burst=%d bytes",
applied.GlobalRateLimitBytesPerSec, applied.GlobalRateBurstBytes, applied.PerClientRateLimitBytesPerSec, applied.PerClientRateBurstBytes)
return nil
}
// UpdatePerClientRateLimit sets the per-client receive rate limit in bytes per
// second and the burst size in bytes, updating all existing client connections.
// The applied burst will be at least [minRateLimitTokenBucketSize]. If bytesPerSec is
// 0, rate limiting is disabled. Mesh peers are always exempt from rate limiting.
func (s *Server) UpdatePerClientRateLimit(bytesPerSec, burst uint64) {
// UpdateRateLimits sets the receive rate limits, updating all existing client
// connections. It returns the applied config, which may differ from rc. If the
// per-client rate limit is 0, rate limiting is disabled. Mesh peers are always
// exempt from rate limiting.
func (s *Server) UpdateRateLimits(rc RateConfig) (applied RateConfig) {
s.mu.Lock()
defer s.mu.Unlock()
s.perClientRecvBytesPerSec = bytesPerSec
s.perClientRecvBurst = max(burst, minRateLimitTokenBucketSize)
if rc.PerClientRateLimitBytesPerSec == 0 {
// if per-client is disabled, all rate limiting is disabled
rc = RateConfig{}
}
if rc.PerClientRateLimitBytesPerSec != 0 {
rc.PerClientRateBurstBytes = max(rc.PerClientRateBurstBytes, minRateLimitTokenBucketSize)
}
if rc.GlobalRateLimitBytesPerSec != 0 {
rc.GlobalRateLimitBytesPerSec = max(rc.GlobalRateLimitBytesPerSec, rc.PerClientRateLimitBytesPerSec)
rc.GlobalRateBurstBytes = max(rc.GlobalRateBurstBytes, minRateLimitTokenBucketSize)
s.recvLim = xrate.NewLimiter(xrate.Limit(rc.GlobalRateLimitBytesPerSec), int(rc.GlobalRateBurstBytes))
} else {
s.recvLim = nil
}
s.rateConfig = rc
for _, cs := range s.clients {
cs.ForeachClient(func(c *sclient) {
c.setRateLimit(s.perClientRecvBytesPerSec, s.perClientRecvBurst)
c.setRateLimit(rc.PerClientRateLimitBytesPerSec, rc.PerClientRateBurstBytes, s.recvLim)
})
}
return rc
}
// HasMeshKey reports whether the server is configured with a mesh key.
@@ -741,7 +758,7 @@ func (s *Server) registerClient(c *sclient) {
s.mu.Lock()
defer s.mu.Unlock()
c.setRateLimit(s.perClientRecvBytesPerSec, s.perClientRecvBurst)
c.setRateLimit(s.rateConfig.PerClientRateLimitBytesPerSec, s.rateConfig.PerClientRateBurstBytes, s.recvLim)
cs, ok := s.clients[c.key]
if !ok {
@@ -1100,7 +1117,7 @@ func (c *sclient) run(ctx context.Context) error {
}
return fmt.Errorf("client %s: readFrameHeader: %w", c.key.ShortString(), err)
}
// Rate limit by DERP frame length (fl), which excludes TLS protocol and
// Rate-limit by DERP frame length (fl), which excludes TLS protocol and
// DERP frame length field overheads.
// Note: meshed clients are exempt from rate limits.
if err := c.rateLimit(int(fl)); err != nil {
@@ -1316,22 +1333,18 @@ func (c *sclient) handleFrameSendPacket(_ derp.FrameType, fl uint32) error {
return c.sendPkt(dst, p)
}
// setRateLimit updates the per-client receive rate limiter.
// When bytesPerSec is 0 or the client is a mesh peer, the limiter is
// set to nil so that [sclient.rateLimit] is a no-op.
func (c *sclient) setRateLimit(bytesPerSec uint64, burst uint64) {
// setRateLimit updates the receive rate limiter. When bytesPerSec is 0 or the
// client is a mesh peer, the limiter is set to nil so that [sclient.rateLimit] is a no-op.
func (c *sclient) setRateLimit(bytesPerSec, burst uint64, parent *xrate.Limiter) {
if bytesPerSec == 0 || c.canMesh {
c.recvLim.Store(nil)
return
}
if lim := c.recvLim.Load(); lim != nil {
// Update in place. SetBurst before SetLimit to avoid a transient
// state where a new higher rate exceeds the old lower burst.
lim.SetBurst(int(burst))
lim.SetLimit(xrate.Limit(bytesPerSec))
return
child := xrate.NewLimiter(xrate.Limit(bytesPerSec), int(burst))
lim := &parentChildTokenBuckets{
parent: parent,
child: child,
}
lim := xrate.NewLimiter(xrate.Limit(bytesPerSec), int(burst))
c.recvLim.Store(lim)
}
@@ -1350,12 +1363,18 @@ func (c *sclient) rateLimit(n int) error {
// [minRateLimitTokenBucketSize].
//
// While we could call WaitN multiple times and/or more precisely for
// lim.Burst(), it's better to return early as a larger DERP frame is:
// 1. unexpected
// 2. only partially read off the socket (bufio)
// lim.Burst(), it's better to return early as a larger DERP frame:
// 1. is unexpected
// 2. is only partially read off the socket (bufio)
// 3. would cause the connection to close shortly after rate limiting, anyway.
clampedN := min(n, minRateLimitTokenBucketSize)
return lim.WaitN(c.ctx, clampedN)
err := lim.child.WaitN(c.ctx, clampedN)
if err != nil {
return err
}
if lim.parent != nil {
return lim.parent.WaitN(c.ctx, clampedN)
}
}
return nil
}
@@ -1792,15 +1811,22 @@ type sclient struct {
// through us with a peer we have no record of.
peerGoneLim *rate.Limiter
// recvLim is the per-connection receive rate limiter. When rate
// limiting is enabled for a non-mesh client, it points to an
// [xrate.Limiter]. When rate limiting is disabled or the client is a
// mesh peer, it is nil and [sclient.rateLimit] is a no-op.
// Updated atomically by [sclient.setRateLimitLocked] so that
// [sclient.rateLimit] can load it without holding Server.mu.
// TODO(mikeodr): update to use mono time, requires updates
// to tstime/rate.Limiter
recvLim atomic.Pointer[xrate.Limiter]
// recvLim is the receive rate limiter. When rate limiting is enabled for a
// non-mesh client, it points to a [parentChildTokenBuckets]. When rate limiting
// is disabled or the client is a mesh peer, it is nil and [sclient.rateLimit]
// is a no-op. Updated atomically by [sclient.setRateLimit] so that
// [sclient.rateLimit] can load it without holding [Server.mu].
recvLim atomic.Pointer[parentChildTokenBuckets]
}
// parentChildTokenBuckets contains a parent and child token bucket for the
// purpose of applying in a hierarchical topology.
//
// TODO: consider porting the required APIs from [xrate.Limiter] to [rate.Limiter],
// which is already optimized to use [mono.Time].
type parentChildTokenBuckets struct {
parent *xrate.Limiter // parent may be nil
child *xrate.Limiter // child is always non-nil
}
func (c *sclient) presentFlags() derp.PeerPresentFlags {