Documentation
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Overview ¶
Package health provides a generic health checking framework. The health package works expvar style. By importing the package the debug server is getting a "/debug/health" endpoint that returns the current status of the application. If there are no errors, "/debug/health" will return a HTTP 200 status, together with an empty JSON reply "{}". If there are any checks with errors, the JSON reply will include all the failed checks, and the response will be have an HTTP 503 status.
A Check can either be run synchronously, or asynchronously. We recommend that most checks are registered as an asynchronous check, so a call to the "/debug/health" endpoint always returns immediately. This pattern is particularly useful for checks that verify upstream connectivity or database status, since they might take a long time to return/timeout.
Installing ¶
To install health, just import it in your application:
import "github.com/docker/distribution/health"
You can also (optionally) import "health/api" that will add two convenience endpoints: "/debug/health/down" and "/debug/health/up". These endpoints add "manual" checks that allow the service to quickly be brought in/out of rotation.
import _ "github.com/docker/distribution/registry/health/api"
# curl localhost:5001/debug/health
{}
# curl -X POST localhost:5001/debug/health/down
# curl localhost:5001/debug/health
{"manual_http_status":"Manual Check"}
After importing these packages to your main application, you can start registering checks.
Registering Checks ¶
The recommended way of registering checks is using a periodic Check. PeriodicChecks run on a certain schedule and asynchronously update the status of the check. This allows "CheckStatus()" to return without blocking on an expensive check.
A trivial example of a check that runs every 5 seconds and shuts down our server if the current minute is even, could be added as follows:
func currentMinuteEvenCheck() error {
m := time.Now().Minute()
if m%2 == 0 {
return errors.New("Current minute is even!")
}
return nil
}
health.RegisterPeriodicFunc("minute_even", currentMinuteEvenCheck, time.Second*5)
Alternatively, you can also make use of "RegisterPeriodicThresholdFunc" to implement the exact same check, but add a threshold of failures after which the check will be unhealthy. This is particularly useful for flaky Checks, ensuring some stability of the service when handling them.
health.RegisterPeriodicThresholdFunc("minute_even", currentMinuteEvenCheck, time.Second*5, 4)
The lowest-level way to interact with the health package is calling "Register" directly. Register allows you to pass in an arbitrary string and something that implements "Checker" and runs your check. If your method returns an error with nil, it is considered a healthy check, otherwise it will make the health check endpoint "/debug/health" start returning a 503 and list the specific check that failed.
Assuming you wish to register a method called "currentMinuteEvenCheck() error" you could do that by doing:
health.Register("even_minute", health.CheckFunc(currentMinuteEvenCheck))
CheckFunc is a convenience type that implements Checker.
Another way of registering a check could be by using an anonymous function and the convenience method RegisterFunc. An example that makes the status endpoint always return an error:
health.RegisterFunc("my_check", func() error {
return Errors.new("This is an error!")
}))
Examples ¶
You could also use the health checker mechanism to ensure your application only comes up if certain conditions are met, or to allow the developer to take the service out of rotation immediately. An example that checks database connectivity and immediately takes the server out of rotation on err:
updater = health.NewStatusUpdater()
health.RegisterFunc("database_check", func() error {
return updater.Check()
}))
conn, err := Connect(...) // database call here
if err != nil {
updater.Update(errors.New("Error connecting to the database: " + err.Error()))
}
You can also use the predefined Checkers that come included with the health package. First, import the checks:
import "github.com/docker/distribution/health/checks
After that you can make use of any of the provided checks. An example of using a `FileChecker` to take the application out of rotation if a certain file exists can be done as follows:
health.Register("fileChecker", health.PeriodicChecker(checks.FileChecker("/tmp/disable"), time.Second*5))
After registering the check, it is trivial to take an application out of rotation from the console:
# curl localhost:5001/debug/health
{}
# touch /tmp/disable
# curl localhost:5001/debug/health
{"fileChecker":"file exists"}
You could also test the connectivity to a downstream service by using a "HTTPChecker", but ensure that you only mark the test unhealthy if there are a minimum of two failures in a row:
health.Register("httpChecker", health.PeriodicThresholdChecker(checks.HTTPChecker("https://www.google.pt"), time.Second*5, 2))
Index ¶
- func CheckStatus() map[string]string
- func Register(name string, check Checker)
- func RegisterFunc(name string, check func() error)
- func RegisterPeriodicFunc(name string, check func() error, period time.Duration)
- func RegisterPeriodicThresholdFunc(name string, check func() error, period time.Duration, threshold int)
- func StatusHandler(w http.ResponseWriter, r *http.Request)
- type CheckFunc
- type Checker
- type Updater
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func CheckStatus ¶
CheckStatus returns a map with all the current health check errors
func Register ¶
Register associates the checker with the provided name. We allow overwrites to a specific check status.
func RegisterFunc ¶
RegisterFunc allows the convenience of registering a checker directly from an arbitrary func() error
func RegisterPeriodicFunc ¶
RegisterPeriodicFunc allows the convenience of registering a PeriodicChecker from an arbitrary func() error
func RegisterPeriodicThresholdFunc ¶
func RegisterPeriodicThresholdFunc(name string, check func() error, period time.Duration, threshold int)
RegisterPeriodicThresholdFunc allows the convenience of registering a PeriodicChecker from an arbitrary func() error
func StatusHandler ¶
func StatusHandler(w http.ResponseWriter, r *http.Request)
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
Types ¶
type CheckFunc ¶
type CheckFunc func() error
CheckFunc is a convenience type to create functions that implement the Checker interface
type Checker ¶
type Checker interface {
// Check returns nil if the service is okay.
Check() error
}
Checker is the interface for a Health Checker
func PeriodicChecker ¶
PeriodicChecker wraps an updater to provide a periodic checker
Source Files
Directories