Docker持久化存储

　　Docker的镜像是只读的，但是容器是可写的，我们可以将数据写入到容器，不过一旦容器删除数据将会丢失，那么有什么办法能将数据进行持久化存储呢？

一、Data Volume

在执行docker run 时，通过-v参数将主机目录作为容器的数据卷，这就是基于本地文件系统Volumn管理。

1、Volume类型

受管理的Volume，由docker后台自动创建
绑定挂载的Volume，具体挂载位置由用户指定

2、docker后台自动创建

以mysql镜像为例说明，进入到https://hub.docker.com/_/mysql查看详情。

启动docker服务

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

拉取mysql镜像

[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：如果出现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这种问题，可以尝试修改/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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运行mysql镜像

[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

这样就启动了一个mysql的容器mysql1，但是显然我们并没有指定数据库中表指定放到什么地方，那么它给我们自动放到什么地方了呢？

我们可以看看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  #持久化存储
# 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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实际上已经帮我们持久化存储到主机的/var/lib/mysql目录中了。

另外可以看到主机上有一条volume的记录：

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

可以看看这个存储卷记录的具体信息：

[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"
    }
]

持久化存储

如果我们讲这个容器删掉，这个存储卷还存在吗？可以尝试一下：

[root@docker-node1 ~]# docker rm -f mysql1 #删掉mysql1容器
mysql1
[root@docker-node1 ~]# docker volume ls #存储卷仍旧存在
DRIVER              VOLUME NAME
local               5c4fbbc613e046baf9e148a301ef94ef09e4fc57312edd907885336e9ecd5bc1

可以看到虽然mysql的容器不在了，但是它的存储卷依旧存在。

3、用户指定挂载位置

上面你也许已经看到了一些需要自定义的地方：其一，volume name的名字太长了，需要自己指定；其二，volume持久化的目录需要自己指定。

容器重命名以及指定挂载位置

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

上面通过-v参数指定mysql的挂载位置（主机文件位置：容器文件位置[Dockerfile中已经指定]），通过--name指定容器的名称，如下所示：

[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

测试持久化

现在，可以先进入到这个容器中，对mysql的数据库中做一些改变，然后删掉容器：

（1）进入容器

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

（2）进入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）创建test数据库

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）删掉mysql1容器

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

（5）新建mysql2容器

新建mysql2容器，并且指向mysql1容器的存储卷：

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

然后可以进入到mysql2容器中查看mysql中是否有mysql1容器创建的test数据库：

[root@docker-node1 ~]# docker exec -it mysql2 /bin/sh #进入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)

可以看到却是存在test数据库，这样也就实现了volume持久化。

二、Bind Mounting

1、bing mounting和data volume的区别

data volume 需要在 Dockerfile文件中定义 volume，这种方式较多的是将容器映射到本地，实现容器与外部程序共享数据。
bind mounting 只需要 -v 指明容器外部文件夹和容器映射文件夹的对应关系，将本地的文件映射到容器内。

2、bind mounting的应用

在bindmounting-test文件夹中新建两个文件

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

编写Dockerfile文件

FROM nginx     #基础镜像
WORKDIR /usr/share/nginx/html  #工作目录，容器内的目录
COPY index.html .  #将本机当前目录下的index.html文件拷贝到上述工作目录下

编写index.html

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

生成镜像

[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

运行docker-nginx镜像

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

上面通过-p进行了端口暴露，可通过外网访问：

　　但是难道每次修改index.html文件都需要重新生成镜像，然后运行吗？我们可以通过bing mounting进行映射，如果本地文件变了，容器内的就会改变。这样就不会重新生成镜像了。

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

　　可以看到上面我将$(pwd)这个当前路劲的文件，也就是bindmounting-test文件夹中内容映射到容器/usr/share/nginx/html目录下，如果本地bindmounting-test文件夹下有文件更改了，容器中自然会变化。

　　例如，修改本地index.html文件中的内容：

[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>

此时，再刷新页面：

这样当在容器内或者容器外更改映射文件夹内的内容时两边都会改变，很利于开发者在linux进行应用的迭代更新部署。

三、总结

1、完成Data volume的步骤

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

2、完成Bind Mounting的步骤

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

上面的映射关系都是主机：容器

posted @ 2020-02-03 17:03 iveBoy 阅读(5690) 评论(1) 编辑收藏举报

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iveBoy