distribution/health/health.go

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package health
import (
"encoding/json"
"fmt"
"net/http"
"sync"
"time"
"github.com/docker/distribution/context"
)
var (
mutex sync.RWMutex
registeredChecks = make(map[string]Checker)
)
// Checker is the interface for a Health Checker
type Checker interface {
// Check returns nil if the service is okay.
Check() error
}
// CheckFunc is a convenience type to create functions that implement
// the Checker interface
type CheckFunc func() error
// Check Implements the Checker interface to allow for any func() error method
// to be passed as a Checker
func (cf CheckFunc) Check() error {
return cf()
}
// Updater implements a health check that is explicitly set.
type Updater interface {
Checker
// Update updates the current status of the health check.
Update(status error)
}
// updater implements Checker and Updater, providing an asynchronous Update
// method.
// This allows us to have a Checker that returns the Check() call immediately
// not blocking on a potentially expensive check.
type updater struct {
mu sync.Mutex
status error
}
// Check implements the Checker interface
func (u *updater) Check() error {
u.mu.Lock()
defer u.mu.Unlock()
return u.status
}
// Update implements the Updater interface, allowing asynchronous access to
// the status of a Checker.
func (u *updater) Update(status error) {
u.mu.Lock()
defer u.mu.Unlock()
u.status = status
}
// NewStatusUpdater returns a new updater
func NewStatusUpdater() Updater {
return &updater{}
}
// thresholdUpdater implements Checker and Updater, providing an asynchronous Update
// method.
// This allows us to have a Checker that returns the Check() call immediately
// not blocking on a potentially expensive check.
type thresholdUpdater struct {
mu sync.Mutex
status error
threshold int
count int
}
// Check implements the Checker interface
func (tu *thresholdUpdater) Check() error {
tu.mu.Lock()
defer tu.mu.Unlock()
if tu.count >= tu.threshold {
return tu.status
}
return nil
}
// thresholdUpdater implements the Updater interface, allowing asynchronous
// access to the status of a Checker.
func (tu *thresholdUpdater) Update(status error) {
tu.mu.Lock()
defer tu.mu.Unlock()
if status == nil {
tu.count = 0
} else if tu.count < tu.threshold {
tu.count++
}
tu.status = status
}
// NewThresholdStatusUpdater returns a new thresholdUpdater
func NewThresholdStatusUpdater(t int) Updater {
return &thresholdUpdater{threshold: t}
}
// PeriodicChecker wraps an updater to provide a periodic checker
func PeriodicChecker(check Checker, period time.Duration) Checker {
u := NewStatusUpdater()
go func() {
t := time.NewTicker(period)
for {
<-t.C
u.Update(check.Check())
}
}()
return u
}
// PeriodicThresholdChecker wraps an updater to provide a periodic checker that
// uses a threshold before it changes status
func PeriodicThresholdChecker(check Checker, period time.Duration, threshold int) Checker {
tu := NewThresholdStatusUpdater(threshold)
go func() {
t := time.NewTicker(period)
for {
<-t.C
tu.Update(check.Check())
}
}()
return tu
}
// CheckStatus returns a map with all the current health check errors
func CheckStatus() map[string]string { // TODO(stevvooe) this needs a proper type
mutex.RLock()
defer mutex.RUnlock()
statusKeys := make(map[string]string)
for k, v := range registeredChecks {
err := v.Check()
if err != nil {
statusKeys[k] = err.Error()
}
}
return statusKeys
}
// Register associates the checker with the provided name. We allow
// overwrites to a specific check status.
func Register(name string, check Checker) {
mutex.Lock()
defer mutex.Unlock()
_, ok := registeredChecks[name]
if ok {
panic("Check already exists: " + name)
}
registeredChecks[name] = check
}
// RegisterFunc allows the convenience of registering a checker directly
// from an arbitrary func() error
func RegisterFunc(name string, check func() error) {
Register(name, CheckFunc(check))
}
// RegisterPeriodicFunc allows the convenience of registering a PeriodicChecker
// from an arbitrary func() error
func RegisterPeriodicFunc(name string, period time.Duration, check CheckFunc) {
Register(name, PeriodicChecker(CheckFunc(check), period))
}
// RegisterPeriodicThresholdFunc allows the convenience of registering a
// PeriodicChecker from an arbitrary func() error
func RegisterPeriodicThresholdFunc(name string, period time.Duration, threshold int, check CheckFunc) {
Register(name, PeriodicThresholdChecker(CheckFunc(check), period, threshold))
}
// StatusHandler returns a JSON blob with all the currently registered Health Checks
// and their corresponding status.
// Returns 503 if any Error status exists, 200 otherwise
func StatusHandler(w http.ResponseWriter, r *http.Request) {
if r.Method == "GET" {
checks := CheckStatus()
status := http.StatusOK
// If there is an error, return 503
if len(checks) != 0 {
status = http.StatusServiceUnavailable
}
statusResponse(w, r, status, checks)
} else {
http.NotFound(w, r)
}
}
// Handler returns a handler that will return 503 response code if the health
// checks have failed. If everything is okay with the health checks, the
// handler will pass through to the provided handler. Use this handler to
// disable a web application when the health checks fail.
func Handler(handler http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
checks := CheckStatus()
if len(checks) != 0 {
statusResponse(w, r, http.StatusServiceUnavailable, checks)
return
}
handler.ServeHTTP(w, r) // pass through
})
}
// statusResponse completes the request with a response describing the health
// of the service.
func statusResponse(w http.ResponseWriter, r *http.Request, status int, checks map[string]string) {
p, err := json.Marshal(checks)
if err != nil {
context.GetLogger(context.Background()).Errorf("error serializing health status: %v", err)
p, err = json.Marshal(struct {
ServerError string `json:"server_error"`
}{
ServerError: "Could not parse error message",
})
status = http.StatusInternalServerError
if err != nil {
context.GetLogger(context.Background()).Errorf("error serializing health status failure message: %v", err)
return
}
}
w.Header().Set("Content-Type", "application/json; charset=utf-8")
w.Header().Set("Content-Length", fmt.Sprint(len(p)))
w.WriteHeader(status)
if _, err := w.Write(p); err != nil {
context.GetLogger(context.Background()).Errorf("error writing health status response body: %v", err)
}
}
// Registers global /debug/health api endpoint
func init() {
http.HandleFunc("/debug/health", StatusHandler)
}