mirror of https://github.com/hashicorp/consul
78 lines
2.4 KiB
Markdown
78 lines
2.4 KiB
Markdown
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# Go Server Client Connection Tracking
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This package provides a library for network servers to track how many
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concurrent connections they have from a given client address.
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It's designed to be very simple and shared between several HashiCorp products
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that provide network servers and need this kind of control to impose limits on
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the resources that can be consumed by a single client.
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## Usage
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### TCP Server
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```
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// During server setup:
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s.limiter = NewLimiter(Config{
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MaxConnsPerClientIP: 10,
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})
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```
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```
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// handleConn is called in its own goroutine for each net.Conn accepted by
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// a net.Listener.
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func (s *Server) handleConn(conn net.Conn) {
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defer conn.Close()
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// Track the connection
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free, err := s.limiter.Accept(conn)
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if err != nil {
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// Not accepted as limit has been reached (or some other error), log error
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// or warning and close.
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// The standard err.Error() message when limit is reached is generic so it
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// doesn't leak information which may potentially be sensitive (e.g. current
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// limits set or number of connections). This also allows comparison to
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// ErrPerClientIPLimitReached if it's important to handle it differently
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// from an internal library or io error (currently not possible but might be
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// in the future if additional functionality is added).
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// If you would like to log more information about the current limit that
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// can be obtained with s.limiter.Config().
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return
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}
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// Defer a call to free to decrement the counter for this client IP once we
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// are done with this conn.
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defer free()
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// Handle the conn
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}
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```
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### HTTP Server
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```
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lim := NewLimiter(Config{
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MaxConnsPerClientIP: 10,
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})
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s := http.Server{
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// Other config here
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ConnState: lim.HTTPConnStateFunc(),
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}
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```
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### Dynamic Configuration
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The limiter supports dynamic reconfiguration. At any time, any goroutine may
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call `limiter.SetConfig(c Config)` which will atomically update the config. All
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subsequent calls to `Accept` will use the newly configured limits in their
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decisions and calls to `limiter.Config()` will return the new config.
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Note that if the limits are reduced that will only prevent further connections
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beyond the new limit - existing connections are not actively closed to meet the
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limit. In cases where this is critical it's often preferable to mitigate in a
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more focussed way e.g. by adding an iptables rule that blocks all connections
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from one malicious client without affecting the whole server.
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