README
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HTTP Governor
The httpgovernor package provides an HTTP request concurreny limiter. This is used to protect resources served over HTTP from becoming overloaded.
Documentation
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Overview ¶
Package httpgovernor provides concurrency limiting for a http.Handler.
Index ¶
Constants ¶
This section is empty.
Variables ¶
var DefaultOverloadHandler = http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) { w.WriteHeader(http.StatusServiceUnavailable) w.Write([]byte("Overloaded")) })
DefaultOverloadHandler is the default handler used in an overload condition.
Functions ¶
Types ¶
type CostEstimator ¶
type CostEstimator interface {
// EstimateCost calculates the relative cost of a request, that is
// the amount of concurrency points required to acquire before
// servicing the request. If the cost is 0 then the request will
// be actioned, even if there are others queued.
EstimateCost(req *http.Request) int64
}
A CostEstimator is used to determine the cost of a request.
type Counter ¶
type Counter interface {
// Inc increments the counter by 1.
Inc()
}
A Counter is used to monitor a monotonically increasing value.
type Gauge ¶
type Gauge interface {
// Inc increments the gauge value by 1.
Inc()
// Dec decrements the gauge value by 1.
Dec()
}
A Gauge is used to monitor the size of the request queue.
type Observer ¶
type Observer interface {
// Observe records the length of time (in seconds) a request had
// to wait in the queue.
Observe(float64)
}
An Observer is used to monitor the time taken for an action to complete.
type Params ¶
type Params struct {
// MaxConcurrency specifies the maximum level of concurrency
// allowed by the governor. If this is 0 then concurrency will
// not be governed.
MaxConcurrency int64
// MaxBurst specifies the maximum level of concurrency before
// requests are failed without queueing. If this is 0 then no
// requests will be queued. The maximum queue size is roughly
// equivilent to MaxBurst-MaxConcurrency.
MaxBurst int64
// MaxQueueDuration specifies the maximum time a request should
// be queued before being aborted. If this is 0 then a default
// duration of 10s will be used.
MaxQueueDuration time.Duration
// OverloadHandler is the http.Handler used to handle requests
// that have to be dropped due to the server being overloaded. If
// this is nil then DefaultOverloadHandler will be used.
OverloadHandler http.Handler
// CostEstimator is used to determine the relative cost of a
// request. If this is nil all requests will be assumed to have a
// cost of 1.
CostEstimator CostEstimator
// RequestOverloadCounter is a counter that is incremented for
// every request dropped because the server is overloaded.
RequestOverloadCounter Counter
// QueueLengthGauge is used to monitor the number of requests
// queued by the governor.
QueueLengthGauge Gauge
// QueueDurationObserver is used to monitor the time succesful
// requests are queued before being actioned.
QueueDurationObserver Observer
}
type PathCostEstimator ¶
A PathCostEstimator determines the cost of a request by matching the path of the URL.
func (PathCostEstimator) EstimateCost ¶
func (c PathCostEstimator) EstimateCost(req *http.Request) int64
EstimateCost determines the cost of the given request by matching in the PathCostEstimator. Any path not specified is assumed to have a cost of 1.
type PatternCostEstimator ¶ added in v0.2.0
type PatternCostEstimator struct {
// contains filtered or unexported fields
}
A PattenCostEstimator determines the cost of a request by matching the request against a list of configured patterns.
The supported patterns are similar to the ones used in http.ServeMux. A path must either be a rooted path, or a rooted subtree. As in http.ServeMux the longest match takes precedence.
A pattern may include a host before the path. If a host is specified only requests addressed to that host will be matched. Any host-specific match will take precedence over all-host matches.
func (*PatternCostEstimator) EstimateCost ¶ added in v0.2.0
func (c *PatternCostEstimator) EstimateCost(req *http.Request) int64
EstimateCost determines the cost of the given request by matching in the PatternCostEstimator. Any path not known is assumed to have a cost of 1.
func (*PatternCostEstimator) SetCost ¶ added in v0.2.0
func (c *PatternCostEstimator) SetCost(path string, cost int64)
SetCost configures the cost of a matched pattern.
Source Files