再一次的 Docker ：多重容器篇

（接續本地篇和雲端篇）

Craig Wyzik from Olympia, WA, USA, File:Hanjin Hamburg (ship, 2011) 003.jpg, CC BY 2.0 https://creativecommons.org/licenses/by/2.0, via Wikimedia Commons

Dockerize apps

Why multi-container

• 容器的特色為隔絕（isolation）。把容器們的服務（service）隔絕起來是個好主意。

Food Trucks

• http://github.com/prakhar1989/FoodTrucks
• Elasticsearch

Two containers

這個程式會需要兩個程序的容器：

• Flask
• Elasticsearch (ES)

The Elasticsearch Image

Official image

docker pull docker.elastic.co/elasticsearch/elasticsearch:6.3.2
docker run -d --name es -p 9200:9200 -p 9300:9300 -e "discovery.type=single-node" docker.elastic.co/elasticsearch/elasticsearch:6.3.2

• --name es
• docker container ls
• docker container logs es
• curl 0.0.0.0:9200

flask and dockerfile

Dockerfile

Type...

docker run -P --rm yourusername/foodtrucks-web
Unable to connect to ES. Retying in 5 secs...
Unable to connect to ES. Retying in 5 secs...
Unable to connect to ES. Retying in 5 secs...
Out of retries. Bailing out...

為什麼上不了呢？

Docker Network

0.0.0.0 是宿主端訪問 ES 容器的 IP。其他容器不能靠 0.0.0.0 訪問 ES 容器。

The IP 0.0.0.0 is the IP to access ES container from the host machine. Another container will not be able to access this on the same IP address.

If it's not 0.0.0.0, which IP address will the container accessed?

docker 裝好後，一開始就會建立三個網路實體：

docker network ls
NETWORK ID          NAME                DRIVER              SCOPE
c2c695315b3a        bridge              bridge              local
a875bec5d6fd        host                host                local
ead0e804a67b        none                null                local

• bridge: 橋接。預設網路容器。

The problem

1. Flask 容器該怎麼知道 es 就是 172.17.0.2 呢？如果 IP 變動的話，又該怎麼辦呢？
2. bridge 網路並不安全，因為因為所有容器都能訪問它。如何阻絕我們自己的網路呢？

答案：

Define our own networks while keeping them isolated using the docker network command.

network create

docker network create foodtrucks-net
docker network ls

docker container stop es
docker container rm es
docker run -d --name es --net foodtrucks-net -p 9200:9200 -p 9300:9300 -e "discovery.type=single-node" docker.elastic.co/elasticsearch/elasticsearch:6.3.2
docker network inspect foodtrucks-net
docker run -it --rm --net foodtrucks-net yourusername/foodtrucks-web bash

再度試試 http://0.0.0.0:5000 吧。

Script

setup-docker.sh

git clone https://github.com/prakhar1989/FoodTrucks
cd FoodTrucks
./setup-docker.sh

Docker Compose

• 用途：輕鬆建立並執行多個 docker 程式。
• 檔案： docker-compose.yml
• 原本是 Fig 專案演變的。
• 用途：
  • production
  • staging
  • development
  • testing
  • CI workflow

docker-compose.YML

API

services:
    es:
        image: docker.elastic.co/elasticsearch/elasticsearch:6.3.2
        container_name: es
        environment:
            - discovery.type=single-node
        ports:
            - 9200:9200
        volumes:
            - esdata1:/usr/share/elasticsearch/data
    web:
        image: yourusername/foodtrucks-web
        command: python3 app.py
        depends_on:
            - es
        ports:
            - 5000:5000
        volumes:
            - ./flask-app:/opt/flask-app

• image: 必須。
• volumes: 容器掛載點。程式的所在。
• depends_on: 要先開 depends_on 指定的容器，才能開現在這個容器。

Startup Docker Compose

1. Go to the directory docker-compose.yml existed.
2. Stop and remove old containers by running docker stop and docker rm.
3. Run docker-compose up.

Let's stop the services and re-run in detached mode...

1. CTRL+C
2. docker-compose up -d
3. docker-compose ps and docker network inspect
4. docker-compose down -v to stop the app

What Next?

我打算實戰、給專案添加合適的 Volume, 再看看能不能上 GCP。