How to fix Health check failed after maximum retries in Docker

# View current container status
docker ps -a

# Get detailed health check information
docker inspect --format='{{json .State.Health}}' <container_name> | jq .

# View the last several health check results with timestamps
docker inspect <container_name> | jq '.[0].State.Health.Log'

{
  "Status": "unhealthy",
  "FailingStreak": 3,
  "Log": [
    {
      "Start": "2024-01-15T10:00:00.000Z",
      "End": "2024-01-15T10:00:30.000Z",
      "ExitCode": 1,
      "Output": "curl: (7) Failed to connect to localhost port 8080"
    },
    {
      "Start": "2024-01-15T10:00:30.000Z",
      "End": "2024-01-15T10:01:00.000Z",
      "ExitCode": 1,
      "Output": "curl: (7) Failed to connect to localhost port 8080"
    },
    {
      "Start": "2024-01-15T10:01:00.000Z",
      "End": "2024-01-15T10:01:30.000Z",
      "ExitCode": 1,
      "Output": "curl: (7) Failed to connect to localhost port 8080"
    }
  ]
}

services:
  api:
    image: my-api:latest
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:8080/health"]
      interval: 30s
      timeout: 10s
      retries: 5  # Increased from default 3
      start_period: 60s

HEALTHCHECK --interval=30s --timeout=10s --retries=5 --start-period=60s \
  CMD curl -f http://localhost:8080/health || exit 1

services:
  backend:
    image: spring-app:latest
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:8080/actuator/health"]
      interval: 10s
      timeout: 5s
      retries: 3
      start_period: 120s  # 2 minutes for JVM warmup

services:
  postgres:
    image: postgres:15
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres"]
      interval: 10s
      timeout: 5s
      retries: 5
      start_period: 30s

services:
  api:
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:8080/health/deep"]
      interval: 30s
      timeout: 30s  # Increased for deep health checks
      retries: 3
      start_period: 60s

# Time how long the health check takes
docker exec <container> time curl -f http://localhost:8080/health

# Get a shell in the container
docker exec -it <container_name> sh

# Run the health check command manually
curl -f http://localhost:8080/health
echo "Exit code: $?"

# Check if the service is listening
netstat -tlnp | grep 8080
# or
ss -tlnp | grep 8080

sh: curl: not found

curl: (7) Failed to connect to localhost port 8080: Connection refused

curl: (22) The requested URL returned error: 503

curl: (6) Could not resolve host: localhost

FROM node:20-alpine
RUN apk add --no-cache curl
# ... rest of Dockerfile

FROM python:3.12-slim
RUN apt-get update && apt-get install -y curl && rm -rf /var/lib/apt/lists/*
# ... rest of Dockerfile

healthcheck:
  test: ["CMD", "wget", "--spider", "-q", "http://localhost:8080/health"]

# Node.js - no extra dependencies needed
healthcheck:
  test: ["CMD", "node", "-e", "require('http').get('http://localhost:8080/health', (r) => process.exit(r.statusCode === 200 ? 0 : 1)).on('error', () => process.exit(1))"]

healthcheck:
  test: ["CMD", "nc", "-z", "localhost", "8080"]

# WRONG - arguments combined
healthcheck:
  test: ["CMD", "curl -f http://localhost:8080/health"]

# CORRECT - arguments separated
healthcheck:
  test: ["CMD", "curl", "-f", "http://localhost:8080/health"]

# CORRECT - shell form handles || exit 1
healthcheck:
  test: ["CMD-SHELL", "curl -f http://localhost:8080/health || exit 1"]

# CORRECT - string is automatically run in shell
healthcheck:
  test: curl -f http://localhost:8080/health || exit 1

docker exec <container> curl -v http://localhost:8080/health

app.get('/health', (req, res) => {
  // Quick check that the server is responding
  res.status(200).json({ status: 'healthy' });
});

// More thorough check including dependencies
app.get('/health/ready', async (req, res) => {
  try {
    await db.query('SELECT 1');
    res.status(200).json({ status: 'ready' });
  } catch (err) {
    res.status(503).json({ status: 'not ready', error: err.message });
  }
});

@app.get("/health")
async def health():
    return {"status": "healthy"}

@app.get("/health/ready")
async def ready():
    try:
        await database.execute("SELECT 1")
        return {"status": "ready"}
    except Exception as e:
        raise HTTPException(status_code=503, detail=str(e))

# PostgreSQL
test: ["CMD-SHELL", "pg_isready -U postgres -d mydb"]

# MySQL
test: ["CMD", "mysqladmin", "ping", "-h", "localhost", "-u", "root", "-p$MYSQL_ROOT_PASSWORD"]

# Redis
test: ["CMD", "redis-cli", "ping"]

# MongoDB
test: ["CMD", "mongosh", "--eval", "db.adminCommand('ping')"]