Dockerのコンテナログ管理入門！ドライバ設定と集中監視をわかりやすく解説

# 実行中のコンテナのログを確認
docker logs コンテナ名

# リアルタイムでログを監視（tail -f のような動作）
docker logs -f コンテナ名

# 最新の100行だけを表示
docker logs --tail 100 コンテナ名

# タイムスタンプ付きで表示
docker logs -t コンテナ名

# docker-compose.yml での設定例
version: '3.8'
services:
  web:
    image: nginx
    logging:
      driver: json-file
      options:
        max-size: "10m"
        max-file: "3"

version: '3.8'
services:
  app:
    image: myapp
    logging:
      driver: syslog
      options:
        syslog-address: "tcp://192.168.1.100:514"
        tag: "myapp"

version: '3.8'
services:
  db:
    image: postgres
    logging:
      driver: journald
      options:
        tag: "postgres-db"

version: '3.8'
services:
  web:
    image: nginx:latest
    logging:
      driver: json-file
      options:
        # 1ファイルあたりの最大サイズ
        max-size: "10m"
        # 保持するファイル数
        max-file: "3"
        # ログにラベルを追加
        labels: "service,environment"
        # 環境変数をログに含める
        env: "NODE_ENV,APP_VERSION"
    labels:
      service: "nginx"
      environment: "production"
    environment:
      - NODE_ENV=production
      - APP_VERSION=1.0.0

version: '3.8'

# 共通設定を定義
x-logging: &default-logging
  driver: json-file
  options:
    max-size: "10m"
    max-file: "3"
    compress: "true"

services:
  web:
    image: nginx
    logging: *default-logging
  
  app:
    image: myapp
    logging: *default-logging
  
  db:
    image: postgres
    logging: *default-logging

{
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "10m",
    "max-file": "3",
    "labels": "service,environment",
    "env": "NODE_ENV"
  }
}

# Dockerデーモンの再起動（Linuxの場合）
sudo systemctl restart docker

version: '3.8'

services:
  # アプリケーションコンテナ
  web:
    image: nginx
    logging:
      driver: fluentd
      options:
        fluentd-address: localhost:24224
        tag: nginx.access
  
  app:
    image: myapp
    logging:
      driver: fluentd
      options:
        fluentd-address: localhost:24224
        tag: myapp.logs
  
  # Fluent Bit（ログ収集）
  fluent-bit:
    image: fluent/fluent-bit:latest
    ports:
      - "24224:24224"
      - "24224:24224/udp"
    volumes:
      - ./fluent-bit.conf:/fluent-bit/etc/fluent-bit.conf
      - ./logs:/var/log

[INPUT]
    Name        forward
    Listen      0.0.0.0
    Port        24224

[FILTER]
    Name        parser
    Match       *
    Key_Name    log
    Parser      json

[OUTPUT]
    Name        file
    Match       *
    Path        /var/log
    Format      json

version: '3.8'

services:
  # ログ収集サーバー
  rsyslog:
    image: rsyslog/syslog_appliance_alpine
    ports:
      - "514:514/udp"
      - "514:514/tcp"
    volumes:
      - ./logs:/var/log
  
  # アプリケーション
  web:
    image: nginx
    logging:
      driver: syslog
      options:
        syslog-address: "tcp://rsyslog:514"
        tag: "nginx"
  
  app:
    image: myapp
    logging:
      driver: syslog
      options:
        syslog-address: "tcp://rsyslog:514"
        tag: "myapp"

#!/bin/bash
# error-monitor.sh - エラーログを監視してアラートを出す

LOG_DIR="./logs"
ERROR_PATTERN="ERROR|FATAL|Exception"

tail -F ${LOG_DIR}/*.log | grep -E "${ERROR_PATTERN}" | while read line; do
    echo "[$(date)] 🚨 エラー検出: $line"
    # 必要に応じて通知処理を追加
    # curl -X POST https://your-webhook-url -d "$line"
done

logging:
  driver: json-file
  options:
    max-size: "10m"
    max-file: "3"
    compress: "true"  # 圧縮を有効化

#!/bin/bash
# log-cleanup.sh - 古いログを削除

find /var/lib/docker/containers -name "*.log" -mtime +7 -delete

# 現在のログドライバを確認
docker inspect コンテナ名 | grep LogConfig

# ログドライバサービスの状態確認（Fluent Bitの場合）
docker logs fluent-bit

// Node.jsでの例
function maskSensitiveData(log) {
  return log
    .replace(/password=\S+/gi, 'password=***')
    .replace(/api_key=\S+/gi, 'api_key=***')
    .replace(/token=\S+/gi, 'token=***');
}

console.log(maskSensitiveData('User logged in with password=secret123'));
// 出力: User logged in with password=***