Pierre-Olivier Mercier
660fda9c3a
Registered on the default FlagSet; ListenAndServe intercepts it and exits 0/1 after probing /health on the -listen address. Lets checker-* Dockerfiles add HEALTHCHECK without any main.go change, even though the runtime image is scratch (no shell, no curl, no wget).
81 lines
2.6 KiB
Go
81 lines
2.6 KiB
Go
// Copyright 2020-2026 The happyDomain Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package server
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import (
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"context"
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"flag"
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"fmt"
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"net"
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"net/http"
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"strings"
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"time"
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)
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// healthcheckMode is registered on the default flag set so any consumer that
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// calls flag.Parse() before ListenAndServe (the standard pattern in our
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// checker mains) gets the behaviour for free. When set, ListenAndServe
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// performs a short-lived HTTP probe against /health on the configured listen
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// address and exits 0/1 instead of starting the server. This lets the same
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// binary act as its own Docker HEALTHCHECK probe for scratch images, where
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// no shell, curl or wget is available.
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var healthcheckMode = flag.Bool(
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"healthcheck",
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false,
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"probe /health on the server's listen address and exit 0 if healthy, 1 "+
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"otherwise (intended as a Docker HEALTHCHECK for scratch-based images)",
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)
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// runHealthcheck performs a GET against http://<addr>/health with a short
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// timeout. Returns nil on a 2xx response, an error otherwise. A bind address
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// like ":8080" or "0.0.0.0:8080" is rewritten to dial the loopback interface
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// so the probe targets the local process.
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func runHealthcheck(addr string) error {
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host, port, err := net.SplitHostPort(normalizeHealthcheckAddr(addr))
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if err != nil {
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return fmt.Errorf("invalid listen addr %q: %w", addr, err)
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}
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if host == "" || host == "0.0.0.0" || host == "::" {
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host = "127.0.0.1"
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}
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url := fmt.Sprintf("http://%s/health", net.JoinHostPort(host, port))
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ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
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defer cancel()
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req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
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if err != nil {
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return err
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}
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client := &http.Client{Timeout: 2 * time.Second}
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resp, err := client.Do(req)
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if err != nil {
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return err
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}
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defer resp.Body.Close()
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if resp.StatusCode/100 != 2 {
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return fmt.Errorf("unhealthy: HTTP %d", resp.StatusCode)
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}
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return nil
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}
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func normalizeHealthcheckAddr(a string) string {
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if strings.HasPrefix(a, ":") {
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return "127.0.0.1" + a
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}
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if strings.HasPrefix(a, "[::]:") {
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return "[::1]:" + strings.TrimPrefix(a, "[::]:")
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}
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return a
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}
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