healthcheck

Healthcheck is a library for implementing Kubernetes liveness and readiness probe handlers in your Go application.

Features

• Integrates easily with Kubernetes. This library explicitly separates liveness vs. readiness checks instead of lumping everything into a single category of check.

• Supports asynchronous checks, which run in a background goroutine at a fixed interval. These are useful for expensive checks that you don't want to add latency to the liveness and readiness endpoints.

• Includes a follow useful checks:

  • DNS
  • TCP
  • HTTP
  • database
  • Go runtime.
  • GC max pause
  • MongoDb
  • Redis

Usage

See the GoDoc examples for more detail.

Install dependency

go get -u github.com/gsdenys/healthcheck

Import the package

import "github.com/gsdenys/healthcheck"

Create a healthcheck.Handler:

health := healthcheck.NewHandler()

Configure some application-specific liveness checks (whether the app itself is unhealthy):

// Our app is not happy if we've got more than 100 goroutines running.
health.AddLivenessCheck("goroutine-threshold", goroutine.Count(100))

Configure some application-specific readiness checks (whether the app is ready to serve requests):

// Our app is not ready if we can't resolve our upstream dependency in DNS.
health.AddReadinessCheck("upstream-dep-dns", dns.Resolve("upstream.example.com", 50*time.Millisecond))

// Our app is not ready if we can't connect to our database (`var DB *sql.DB`) in <1s.
health.AddReadinessCheck("database", db.Ping(DB, 1*time.Second))

Expose the /live and /ready endpoints over HTTP (on port 8086):

go func() {
	httpError := http.ListenAndServe("0.0.0.0:8086", health)

	if httpError != nil {
		log.Println("While serving HTTP: ", httpError)
	}
}()

Configure your Kubernetes container with HTTP liveness and readiness probes see the (Kubernetes documentation) for more detail:

# this is a bare bones example
# copy and paste livenessProbe and readinessProbe as appropriate for your app
apiVersion: v1
kind: Pod
metadata:
  name: healthcheck-example
spec:
  containers:
  - name: liveness
    image: your-registry/your-container

    # define a liveness probe that checks every 5 seconds, starting after 5 seconds
    livenessProbe:
      httpGet:
        path: /live
        port: 8086
      initialDelaySeconds: 5
      periodSeconds: 5

    # define a readiness probe that checks every 5 seconds
    readinessProbe:
      httpGet:
        path: /ready
        port: 8086
      periodSeconds: 5

If one of your readiness checks fails, Kubernetes will stop routing traffic to that pod within a few seconds (depending on periodSeconds and other factors).

If one of your liveness checks fails or your app becomes totally unresponsive, Kubernetes will restart your container.

HTTP Endpoints

When you run go http.ListenAndServe("0.0.0.0:8086", health), two HTTP endpoints are exposed:

• /live: liveness endpoint (HTTP 200 if healthy, HTTP 503 if unhealthy)
• /ready: readiness endpoint (HTTP 200 if healthy, HTTP 503 if unhealthy)

Pass the ?full=1 query parameter to see the full check results as JSON. These are omitted by default for performance.