Docker持久化存儲

　　Docker的鏡像是隻讀的，可是容器是可寫的，咱們能夠將數據寫入到容器，不過一旦容器刪除數據將會丟失，那麼有什麼辦法能將數據進行持久化存儲呢？

1、Data Volume

在執行docker run 時，經過-v參數將主機目錄做爲容器的數據卷，這就是基於本地文件系統Volumn管理。

一、Volume類型

• 受管理的Volume，由docker後臺自動建立
• 綁定掛載的Volume，具體掛載位置由用戶指定

二、docker後臺自動建立

以mysql鏡像爲例說明，進入到https://hub.docker.com/_/mysql查看詳情。

• 啓動docker服務

[root@docker-node1 ~]# systemctl start docker

• 拉取mysql鏡像

[root@docker-node1 ~]# docker pull mysql
Using default tag: latest latest: Pulling from library/mysql 619014d83c02: Pulling fs layer 9ced578c3a5f: Pulling fs layer 

注意：若是出現Get https://registry-1.docker.io/v2/library/mysql/manifests/latest: dial tcp: lookup registry-1.docker.io on 8.8.8.8:53: read udp 192.168.0.109:41429->8.8.8.8:53: i/o timeout這種問題，能夠嘗試修改/etc/resolv.conf文件，加入nameserver 8.8.4.4

[root@docker-node1 ~]# cat /etc/resolv.conf # Generated by NetworkManager
nameserver 8.8.8.8 nameserver 8.8.4.4

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• 運行mysql鏡像

[root@docker-node1 ~]# docker run -d --name mysql1 -e MYSQL_ALLOW_EMPTY_PASSWORD=true mysql
9dd537e48f16fd924f19f95aa38d15e08bdfa254d65ee66f1e19331ed6e79ce3 [root@docker-node1 ~]# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 9dd537e48f16 mysql "docker-entrypoint.s…"   20 seconds ago      Up 11 seconds       3306/tcp, 33060/tcp   mysql1

這樣就啓動了一個mysql的容器mysql1，可是顯然咱們並無指定數據庫中表指定放到什麼地方，那麼它給咱們自動放到什麼地方了呢？

咱們能夠看看mysql的Dockerfile：

FROM debian:stretch-slim # add our user and group first to make sure their IDs get assigned consistently, regardless of whatever dependencies get added
RUN groupadd -r mysql && useradd -r -g mysql mysql RUN apt-get update && apt-get install -y --no-install-recommends gnupg dirmngr && rm -rf /var/lib/apt/lists/*

# add gosu for easy step-down from root
ENV GOSU_VERSION 1.7 RUN set -x \ && apt-get update && apt-get install -y --no-install-recommends ca-certificates wget && rm -rf /var/lib/apt/lists/* \ && wget -O /usr/local/bin/gosu "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$(dpkg --print-architecture)" \ && wget -O /usr/local/bin/gosu.asc "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$(dpkg --print-architecture).asc" \ && export GNUPGHOME="$(mktemp -d)" \ && gpg --batch --keyserver ha.pool.sks-keyservers.net --recv-keys B42F6819007F00F88E364FD4036A9C25BF357DD4 \ && gpg --batch --verify /usr/local/bin/gosu.asc /usr/local/bin/gosu \ && gpgconf --kill all \ && rm -rf "$GNUPGHOME" /usr/local/bin/gosu.asc \ && chmod +x /usr/local/bin/gosu \ && gosu nobody true \ && apt-get purge -y --auto-remove ca-certificates wget RUN mkdir /docker-entrypoint-initdb.d RUN apt-get update && apt-get install -y --no-install-recommends \ # for MYSQL_RANDOM_ROOT_PASSWORD
 pwgen \ # for mysql_ssl_rsa_setup
 openssl \ # FATAL ERROR: please install the following Perl modules before executing /usr/local/mysql/scripts/mysql_install_db: # File::Basename # File::Copy # Sys::Hostname # Data::Dumper
 perl \ && rm -rf /var/lib/apt/lists/* RUN set -ex; \ # gpg: key 5072E1F5: public key "MySQL Release Engineering <mysql-build@oss.oracle.com>" imported
    key='A4A9406876FCBD3C456770C88C718D3B5072E1F5'; \ export GNUPGHOME="$(mktemp -d)"; \ gpg --batch --keyserver ha.pool.sks-keyservers.net --recv-keys "$key"; \ gpg --batch --export "$key" > /etc/apt/trusted.gpg.d/mysql.gpg; \ gpgconf --kill all; \ rm -rf "$GNUPGHOME"; \ apt-key list > /dev/null ENV MYSQL_MAJOR 8.0 ENV MYSQL_VERSION 8.0.19-1debian9 RUN echo "deb http://repo.mysql.com/apt/debian/ stretch mysql-${MYSQL_MAJOR}" > /etc/apt/sources.list.d/mysql.list # the "/var/lib/mysql" stuff here is because the mysql-server postinst doesn't have an explicit way to disable the mysql_install_db codepath besides having a database already "configured" (ie, stuff in /var/lib/mysql/mysql) # also, we set debconf keys to make APT a little quieter
RUN { \ echo mysql-community-server mysql-community-server/data-dir select ''; \ echo mysql-community-server mysql-community-server/root-pass password ''; \ echo mysql-community-server mysql-community-server/re-root-pass password ''; \ echo mysql-community-server mysql-community-server/remove-test-db select false; \ } | debconf-set-selections \ && apt-get update && apt-get install -y mysql-community-client="${MYSQL_VERSION}" mysql-community-server-core="${MYSQL_VERSION}" && rm -rf /var/lib/apt/lists/* \ && rm -rf /var/lib/mysql && mkdir -p /var/lib/mysql /var/run/mysqld \ && chown -R mysql:mysql /var/lib/mysql /var/run/mysqld \ # ensure that /var/run/mysqld (used for socket and lock files) is writable regardless of the UID our mysqld instance ends up having at runtime
    && chmod 777 /var/run/mysqld VOLUME /var/lib/mysql  #持久化存儲 # Config files
COPY config/ /etc/mysql/ COPY docker-entrypoint.sh /usr/local/bin/ RUN ln -s usr/local/bin/docker-entrypoint.sh /entrypoint.sh # backwards compat
ENTRYPOINT ["docker-entrypoint.sh"] EXPOSE 3306 33060 CMD ["mysqld"]

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實際上已經幫咱們持久化存儲到主機的/var/lib/mysql目錄中了。

另外能夠看到主機上有一條volume的記錄：

[root@docker-node1 ~]# docker volume ls
DRIVER VOLUME NAME local 5c4fbbc613e046baf9e148a301ef94ef09e4fc57312edd907885336e9ecd5bc1

能夠看看這個存儲卷記錄的具體信息：

[root@docker-node1 ~]# docker volume inspect 5c4fbbc613e046baf9e148a301ef94ef09e4fc57312edd907885336e9ecd5bc1
[ { "CreatedAt": "2020-02-03T13:24:30+08:00", "Driver": "local", "Labels": null, "Mountpoint": "/var/lib/docker/volumes/5c4fbbc613e046baf9e148a301ef94ef09e4fc57312edd907885336e9ecd5bc1/_data", "Name": "5c4fbbc613e046baf9e148a301ef94ef09e4fc57312edd907885336e9ecd5bc1", "Options": null, "Scope": "local" } ]

• 持久化存儲

若是咱們講這個容器刪掉，這個存儲卷還存在嗎？能夠嘗試一下：

[root@docker-node1 ~]# docker rm -f mysql1 #刪掉mysql1容器
mysql1 [root@docker-node1 ~]# docker volume ls #存儲卷仍舊存在
DRIVER VOLUME NAME local 5c4fbbc613e046baf9e148a301ef94ef09e4fc57312edd907885336e9ecd5bc1

能夠看到雖然mysql的容器不在了，可是它的存儲卷依舊存在。

三、用戶指定掛載位置

上面你也許已經看到了一些須要自定義的地方：其一，volume name的名字太長了，須要本身指定；其二，volume持久化的目錄須要本身指定。

• 容器重命名以及指定掛載位置

[root@docker-node1 ~]# docker run -d -v /home/mysql:/var/lib/mysql --name mysql1 -e MYSQL_ALLOW_EMPTY_PASSWORD=true mysql
0e560c5c9caf902c0d9647ef1d7995803d9dfde8e0db2c529d97f913f943bdf5

上面經過-v參數指定mysql的掛載位置（主機文件位置：容器文件位置[Dockerfile中已經指定]），經過--name指定容器的名稱，以下所示：

[root@docker-node1 ~]# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 0e560c5c9caf mysql "docker-entrypoint.s…"   9 seconds ago       Up 7 seconds        3306/tcp, 33060/tcp   mysql1

• 測試持久化

如今，能夠先進入到這個容器中，對mysql的數據庫中作一些改變，而後刪掉容器：

（1）進入容器

[root@docker-node1 ~]# docker exec -it mysql1 /bin/sh

（2）進入mysql

# mysql -uroot
Welcome to the MySQL monitor.  Commands end with ; or \g. Your MySQL connection id is 8 Server version: 8.0.19 MySQL Community Server - GPL Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

（3）建立test數據庫

mysql> create database test; Query OK, 1 row affected (0.36 sec) mysql> show databases; +--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| test               |
+--------------------+
5 rows in set (0.00 sec)

（4）刪掉mysql1容器

[root@docker-node1 ~]# docker rm -f mysql1
mysql1

（5）新建mysql2容器

新建mysql2容器，而且指向mysql1容器的存儲卷：

[root@docker-node1 ~]# docker run -d -v /home/mysql:/var/lib/mysql --name mysql2 -e MYSQL_ALLOW_EMPTY_PASSWORD=true mysql
9fc1aff1e798b0b6b4c01b26160877253c655f137a542734eb81b2b8984af66c

而後能夠進入到mysql2容器中查看mysql中是否有mysql1容器建立的test數據庫：

[root@docker-node1 ~]# docker exec -it mysql2 /bin/sh #進入mysql2容器 # mysql -uroot
Welcome to the MySQL monitor.  Commands end with ; or \g. Your MySQL connection id is 8 Server version: 8.0.19 MySQL Community Server - GPL Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. mysql> show databases; +--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| test               |
+--------------------+
5 rows in set (0.16 sec)

能夠看到倒是存在test數據庫，這樣也就實現了volume持久化。

2、Bind Mounting

一、bing mounting和data volume的區別

• data volume 須要在 Dockerfile文件中 定義 volume，這種方式較多的是將容器映射到本地，實現容器與外部程序共享數據。
• bind mounting 只須要 -v 指明 容器外部文件夾和容器映射文件夾的對應關係，將本地的文件映射到容器內。

二、bind mounting的應用

•  在bindmounting-test文件夾中新建兩個文件

[root@docker-node1 bindmounting-test]# ls
Dockerfile  index.html

• 編寫Dockerfile文件

FROM nginx     #基礎鏡像
WORKDIR /usr/share/nginx/html  #工做目錄，容器內的目錄
COPY index.html .  #將本機當前目錄下的index.html文件拷貝到上述工做目錄下

• 編寫index.html

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>hello</title>
</head>
<body>
  <h1>Hello Docker! </h1>
</body>
</html>

• 生成鏡像

[root@docker-node1 bindmounting-test]# docker build -t docker-nginx .
Sending build context to Docker daemon  3.072kB Step 1/3 : FROM nginx ---> f68d6e55e065 Step 2/3 : WORKDIR /usr/share/nginx/html ---> Running in 3b784d71c4dc Removing intermediate container 3b784d71c4dc ---> 10cef7e9bbb9 Step 3/3 : COPY index.html . ---> f43b1a1b7bef Successfully built f43b1a1b7bef Successfully tagged docker-nginx:latest

• 運行docker-nginx鏡像

[root@docker-node1 bindmounting-test]# docker run -d -p 80:80 --name web docker-nginx
22c28d4887d222785a3c60ca28c2fe79ff82ff9e630af0cdbb48232171732c90

上面經過-p進行了端口暴露，可經過外網訪問：

 　　可是難道每次修改index.html文件都須要從新生成鏡像，而後運行嗎？咱們能夠經過bing mounting進行映射，若是本地文件變了，容器內的就會改變。這樣就不會從新生成鏡像了。

• 使用bind mounting

[root@docker-node1 bindmounting-test]# ls
Dockerfile index.html [root@docker-node1 bindmounting-test]# docker run -d -v $(pwd):/usr/share/nginx/html -p 80:80 --name web docker-nginx
f4661067be3fdead6c627bc00a054244b92207d42baebafdc37b8c8a8fe6f3cb

　　能夠看到上面我將$(pwd)這個當前路勁的文件，也就是bindmounting-test文件夾中內容映射到容器/usr/share/nginx/html目錄下，若是本地bindmounting-test文件夾下有文件更改了，容器中天然會變化。

　　例如，修改本地index.html文件中的內容：

[root@docker-node1 bindmounting-test]# vim index.html

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">

  <title>hello</title>

</head>

<body>
  <h1>Hello </h1>
</body>
</html>

此時，再刷新頁面：

 這樣當在容器內或者容器外更改 映射文件夾內的內容時 兩邊都會改變，很利於開發者在linux進行應用的迭代更新部署。

3、總結

一、完成Data volume的步驟

• Dockerfile中指定volume參數，如 VOLUME  /var/lib/mysql
• docker run -v /home/mysql:/var/lib/mysql

二、完成Bind Mounting的步驟

• docker run -v /home/mysql:/var/lib/mysql 

上面的映射關係都是 主機：容器