docker compose 실습

김승윤·2021년 10월 31일

순서는 다음과 같이 실습하겠습니다.

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도커 컴포즈 설치하기

참고 : https://docs.docker.com/compose/install/

$ sudo curl -L "https://github.com/docker/compose/releases/download/1.29.2/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose
$ sudo chmod +x /usr/local/bin/docker-compose
$ docker-compose --version

컨테이너 빌드에서 운영까지

참고 : https://docs.docker.com/compose/gettingstarted/

Setup

$ mkdir composetest
$ cd composetest

디렉토리 안에 app.py 파일 생성

$ cat > app.py

import time

import redis
from flask import Flask

app = Flask(__name__)
cache = redis.Redis(host='redis', port=6379)

def get_hit_count():
    retries = 5
    while True:
        try:
            return cache.incr('hits')
        except redis.exceptions.ConnectionError as exc:
            if retries == 0:
                raise exc
            retries -= 1
            time.sleep(0.5)

@app.route('/')
def hello():
    count = get_hit_count()
    return 'Hello World! I have been seen {} times.\n'.format(count)

requirements.txt 파일 생성

$ cat > requrements.txt

flask
redis

dockerfile 생성

$ cat > dockerfile

FROM python:3.7-alpine
WORKDIR /code
ENV FLASK_APP=app.py
ENV FLASK_RUN_HOST=0.0.0.0
RUN apk add --no-cache gcc musl-dev linux-headers
COPY requirements.txt requirements.txt
RUN pip install -r requirements.txt
EXPOSE 5000
COPY . .
CMD ["flask", "run"]

compose.yml 생성

$ cat > docker-compose.yml

version: "3.9"
services:
  web:
    build: .
    ports:
      - "5000:5000"
  redis:
    image: "redis:alpine"

build and run

$ docker-compose up

새로고침을 할때마다 바뀌는 것을 확인할 수 있습니다.

만약 다음과 같은 오류가 발생하면 dns 문제일수도 있습니다.

[root@docker composetest]# docker-compose up
Building web
Sending build context to Docker daemon  5.632kB
Step 1/10 : FROM python:3.7-alpine
3.7-alpine: Pulling from library/python
a0d0a0d46f8b: Pull complete
c11246b421be: Pull complete
c5f7759615a9: Pull complete
6dc4dde3f226: Pull complete
9928d5d652ca: Pull complete
Digest: sha256:68dc2f52411f1071069a75c00029a0620d98139d638153cd33d029cf9810c8d6
Status: Downloaded newer image for python:3.7-alpine
 ---> 4d1c95b3db1c
Step 2/10 : WORKDIR /code
 ---> Running in f82a30d1fc05
Removing intermediate container f82a30d1fc05
 ---> 46c3125d0b44
Step 3/10 : ENV FLASK_APP=app.py
 ---> Running in 2a5bf523d475
Removing intermediate container 2a5bf523d475
 ---> 49729e81d96d
Step 4/10 : ENV FLASK_RUN_HOST=0.0.0.0
 ---> Running in 2c6d2dec6f3c
Removing intermediate container 2c6d2dec6f3c
 ---> fb79d97be29b
Step 5/10 : RUN apk add --no-cache gcc musl-dev linux-headers
 ---> Running in db5dd0fa3780
fetch https://dl-cdn.alpinelinux.org/alpine/v3.14/main/x86_64/APKINDEX.tar.gz
WARNING: Ignoring https://dl-cdn.alpinelinux.org/alpine/v3.14/main: temporary error (try again later)
fetch https://dl-cdn.alpinelinux.org/alpine/v3.14/community/x86_64/APKINDEX.tar.gz
WARNING: Ignoring https://dl-cdn.alpinelinux.org/alpine/v3.14/community: temporary error (try again later)
ERROR: unable to select packages:
  gcc (no such package):
    required by: world[gcc]
  linux-headers (no such package):
    required by: world[linux-headers]
  musl-dev (no such package):
    required by: world[musl-dev]
The command '/bin/sh -c apk add --no-cache gcc musl-dev linux-headers' returned a non-zero code: 3
ERROR: Service 'web' failed to build : Build failed

먼저 dns 문제인지 한번 더 확인을 해봅니다.

$ docker run busybox nslookup google.com   # takes a long time
nslookup: can't resolve 'google.com'   # <--- appears after a long time
Server:    8.8.8.8
Address 1: 8.8.8.8

dns가 문제가 있다면

$ nmcli dev show | grep 'IP4.DNS'
IP4.DNS[1]:              168.126.63.1
IP4.DNS[2]:              8.8.8.8

여기서 리스트업 되는 dns 주소들을 /etc/docker/daemon.json 파일에 넣어줍니다.

{                                                                          
    "dns": ["10.0.0.2", "10.0.0.3"]                                                                           
}

docker를 재실행해줍니다.

systemctl restart docker

제가 겪은 문제를 해결한 방식으로 다른 문제일 수도 있습니다.

도커 컴포즈 제거

$ docker-compose down

도커 컴포즈를 제거후 아래 실습을 진행하겠습니다.
(stop 명령어로 중지시킬 수 있습니다.)

볼륨 마운트

docker-compose.yml 파일에 볼륨 명령어를 추가하겠습니다.

version: "3.9"
services:
  web:
    build: .
    ports:
      - "5000:5000"
    volumes:
      - .:/code
    environment:
      FLASK_ENV: development
  redis:
    image: "redis:alpine"

그리고 다시