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feat: add loki health command (backport release-3.6.x) #20590

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Merged
salvacorts merged 1 commit into from
Jan 28, 2026
Merged

feat: add loki health command (backport release-3.6.x) #20590

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72 changes: 72 additions & 0 deletions cmd/loki/health.go
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Original file line number Diff line number Diff line change
@@ -0,0 +1,72 @@
package main

import (
"fmt"
"net/http"
"os"
"regexp"
"time"
)

const (
healthFlag = "health"
defaultHealthURL = "http://localhost:3100/ready"
healthTimeout = 5 * time.Second
)

// CheckHealth checks if args contain the -health flag
func CheckHealth(args []string) bool {
pattern := regexp.MustCompile(`^-+` + healthFlag + `$`)
for _, a := range args {
if pattern.MatchString(a) {
return true
}
}
return false
}

// RunHealthCheck performs a health check against the /ready endpoint
// Returns exit code 0 if healthy, 1 if unhealthy
func RunHealthCheck(args []string) int {

url := getHealthURL(args)

client := &http.Client{
Timeout: healthTimeout,
}

resp, err := client.Get(url)
if err != nil {
fmt.Fprintf(os.Stderr, "Health check failed: %v\n", err)
return 1
}
defer resp.Body.Close()

if resp.StatusCode == http.StatusOK {
fmt.Println("Loki is healthy")
return 0
}

fmt.Fprintf(os.Stderr, "Loki is unhealthy: status code %d\n", resp.StatusCode)
return 1
}

// getHealthURL extracts the URL from args or returns default
// Looks for -health.url=<url> or -health.url <url>
func getHealthURL(args []string) string {
urlPattern := regexp.MustCompile(`^-+health\.url[=:]?(.*)$`)
healthArgPattern := regexp.MustCompile(`^-`)

for i, a := range args {
if matches := urlPattern.FindStringSubmatch(a); matches != nil {
if matches[1] != "" {
return matches[1]
}
// Check next argument for the URL value
if i+1 < len(args) && !healthArgPattern.MatchString(args[i+1]) {
return args[i+1]
}
}
}
return defaultHealthURL
}
6 changes: 6 additions & 0 deletions cmd/loki/main.go
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,12 @@ func main() {

var config loki.ConfigWrapper

// Health check command - runs before any config parsing
// Usage: loki -health [-health.url=http://localhost:3100/ready]
if CheckHealth(os.Args[1:]) {
os.Exit(RunHealthCheck(os.Args[1:]))
}

if loki.PrintVersion(os.Args[1:]) {
fmt.Println(version.Print("loki"))
os.Exit(0)
Expand Down
26 changes: 22 additions & 4 deletions production/docker/docker-compose.yaml
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Original file line number Diff line number Diff line change
Expand Up @@ -14,10 +14,6 @@ services:
init:
image: &lokiImage grafana/loki:latest
user: root
entrypoint:
- "chown"
- "10001:10001"
- "/loki"
volumes:
- ./loki:/loki
networks:
Expand Down Expand Up @@ -57,6 +53,7 @@ services:
# for testing purposes only, disable in production
log-generator:
image: mingrammer/flog
platform: linux/amd64
command:
- --loop
- --format=json
Expand Down Expand Up @@ -132,6 +129,13 @@ services:
deploy:
mode: replicated
replicas: 3
# Native healthcheck using loki -health command (no shell required)
healthcheck:
test: ["CMD", "/usr/bin/loki", "-health"]
start_period: 30s
interval: 30s
timeout: 10s
retries: 3

loki-write:
image: *lokiImage
Expand All @@ -154,6 +158,13 @@ services:
deploy:
mode: replicated
replicas: 3
# Native healthcheck using loki -health command (no shell required)
healthcheck:
test: ["CMD", "/usr/bin/loki", "-health"]
start_period: 30s
interval: 30s
timeout: 10s
retries: 3

loki-backend:
image: *lokiImage
Expand All @@ -177,6 +188,13 @@ services:
deploy:
mode: replicated
replicas: 3
# # Native healthcheck using loki -health command (no shell required)
healthcheck:
test: ["CMD", "/usr/bin/loki", "-health"]
start_period: 30s
interval: 30s
timeout: 10s
retries: 3

# alertmanager to enable receiving alerts
alertmanager:
Expand Down