registry/health/health.go
Aaron Lehmann b9b9cafa8f Expose a Registry type in health package, so unit tests can stay isolated from each other
Update docs.

Change health_test.go tests to create their own registries and register
the checks there. The tests now call CheckStatus directly instead of
polling the HTTP handler, which returns results from the default
registry.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
2015-08-20 15:07:54 -07:00

306 lines
8.7 KiB
Go

package health
import (
"encoding/json"
"fmt"
"net/http"
"sync"
"time"
"github.com/docker/distribution/context"
"github.com/docker/distribution/registry/api/errcode"
)
// A Registry is a collection of checks. Most applications will use the global
// registry defined in DefaultRegistry. However, unit tests may need to create
// separate registries to isolate themselves from other tests.
type Registry struct {
mu sync.RWMutex
registeredChecks map[string]Checker
}
// NewRegistry creates a new registry. This isn't necessary for normal use of
// the package, but may be useful for unit tests so individual tests have their
// own set of checks.
func NewRegistry() *Registry {
return &Registry{
registeredChecks: make(map[string]Checker),
}
}
// DefaultRegistry is the default registry where checks are registered. It is
// the registry used by the HTTP handler.
var DefaultRegistry *Registry
// 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 (registry *Registry) CheckStatus() map[string]string { // TODO(stevvooe) this needs a proper type
registry.mu.RLock()
defer registry.mu.RUnlock()
statusKeys := make(map[string]string)
for k, v := range registry.registeredChecks {
err := v.Check()
if err != nil {
statusKeys[k] = err.Error()
}
}
return statusKeys
}
// CheckStatus returns a map with all the current health check errors from the
// default registry.
func CheckStatus() map[string]string {
return DefaultRegistry.CheckStatus()
}
// Register associates the checker with the provided name.
func (registry *Registry) Register(name string, check Checker) {
if registry == nil {
registry = DefaultRegistry
}
registry.mu.Lock()
defer registry.mu.Unlock()
_, ok := registry.registeredChecks[name]
if ok {
panic("Check already exists: " + name)
}
registry.registeredChecks[name] = check
}
// Register associates the checker with the provided name in the default
// registry.
func Register(name string, check Checker) {
DefaultRegistry.Register(name, check)
}
// RegisterFunc allows the convenience of registering a checker directly from
// an arbitrary func() error.
func (registry *Registry) RegisterFunc(name string, check func() error) {
registry.Register(name, CheckFunc(check))
}
// RegisterFunc allows the convenience of registering a checker in the default
// registry directly from an arbitrary func() error.
func RegisterFunc(name string, check func() error) {
DefaultRegistry.RegisterFunc(name, check)
}
// RegisterPeriodicFunc allows the convenience of registering a PeriodicChecker
// from an arbitrary func() error.
func (registry *Registry) RegisterPeriodicFunc(name string, period time.Duration, check CheckFunc) {
registry.Register(name, PeriodicChecker(CheckFunc(check), period))
}
// RegisterPeriodicFunc allows the convenience of registering a PeriodicChecker
// in the default registry from an arbitrary func() error.
func RegisterPeriodicFunc(name string, period time.Duration, check CheckFunc) {
DefaultRegistry.RegisterPeriodicFunc(name, period, check)
}
// RegisterPeriodicThresholdFunc allows the convenience of registering a
// PeriodicChecker from an arbitrary func() error.
func (registry *Registry) RegisterPeriodicThresholdFunc(name string, period time.Duration, threshold int, check CheckFunc) {
registry.Register(name, PeriodicThresholdChecker(CheckFunc(check), period, threshold))
}
// RegisterPeriodicThresholdFunc allows the convenience of registering a
// PeriodicChecker in the default registry from an arbitrary func() error.
func RegisterPeriodicThresholdFunc(name string, period time.Duration, threshold int, check CheckFunc) {
DefaultRegistry.RegisterPeriodicThresholdFunc(name, period, threshold, check)
}
// 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 {
errcode.ServeJSON(w, errcode.ErrorCodeUnavailable.
WithDetail("health check failed: please see /debug/health"))
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, creates default registry
func init() {
DefaultRegistry = NewRegistry()
http.HandleFunc("/debug/health", StatusHandler)
}