OpenShift_068：构建一个简单的 S2I Builder Image（基于 centos7）

环境：MAC OS X 10.12.3 + Docker 1.13.1 + S2I 1.1.5

本文构建一个 lighttpd builder image，比较简单，旨在了解构建 S2I Builder Image 的主要步骤和原理。
以下操作均在 MAC 机器上执行。

1. 下载并安装 S2I 工具
下载地址：https://github.com/openshift/source-to-image/releases
下载介质：source-to-image-v1.1.5-4dd7721-darwin-amd64.tar.gz
安装
tar zxvf source-to-image-v1.1.5-4dd7721-darwin-amd64.tar.gz
mv s2i sti /usr/local/bin/

2. 创建 S2I 目录结构
s2i create lighttpd-centos7 s2i-lighttpd
说明：这里 lighttpd-centos7 是 builder image 名称，s2i-lighttpd 是目录名称。
在 s2i-lighttpd 目录下有：
（1）Dockerfile – 定义 builder image
（2）Makefile – 包含构建 builder image 和测试 builder image 的脚本
（3）test/
  （3.1）run – 测试脚本
  （3.2）test-app/ – 要测试应用
（4）.s2i/bin/
  （4.1）assemble – 构建应用的脚本
  （4.2）run – 运行应用的脚本
  （4.3）save-artifacts – 增量构建的脚本
  （4.4）usage – 如何使用 builder image 的帮助脚本

3. 定义 Docker file
内容如下：
# We are basing our builder image on openshift base-centos7 image
FROM openshift/base-centos7

# Inform users who's the maintainer of this builder image
MAINTAINER Ma Ping <pma@redhat.com>

# Inform about software versions being used inside the builder
ENV LIGHTTPD_VERSION=1.4.45

# Set labels used in OpenShift to describe the builder images
LABEL io.k8s.description="Platform for serving static HTML files" \
      io.k8s.display-name="Lighttpd 1.4.45" \
      io.openshift.expose-services="8080:http" \
      io.openshift.tags="builder,html,lighttpd"

# Install the required software, namely Lighttpd and
COPY CentOS7-Base-163.repo /etc/yum.repos.d/CentOS7-Base-163.repo
RUN yum install -y epel-release && \
    yum install -y lighttpd && \
    # clean yum cache files, as they are not needed and will only make the image bigger in the end
    yum clean all -y

# Defines the location of the S2I
# Although this is defined in openshift/base-centos7 image it's repeated here
# to make it clear why the following COPY operation is happening
LABEL io.openshift.s2i.scripts-url=image:///usr/local/s2i
# Copy the S2I scripts from ./.s2i/bin/ to /usr/local/s2i when making the builder image
COPY ./.s2i/bin/ /usr/local/s2i

# Copy the lighttpd configuration file
COPY ./etc/ /opt/app-root/etc

# Drop the root user and make the content of /opt/app-root owned by user 1001
RUN chown -R 1001:1001 /opt/app-root

# Set the default user for the image, the user itself was created in the base image
USER 1001

# Specify the ports the final image will expose
EXPOSE 8080

# Set the default CMD to print the usage of the image, if somebody does docker run
CMD ["usage"]

4. 定义 s2i/bin/assemble
内容如下：
#!/bin/bash -e
#
# S2I assemble script for the 'lighttpd-centos7' image.
# The 'assemble' script builds your application source ready to run.
#
# For more information refer to the documentation:
#  https://github.com/openshift/source-to-image/blob/master/docs/builder_image.md
#

echo "---> Installing application source"
cp -Rf /tmp/src/. ./

说明：默认情况下，s2i 构建过程会把应用源代码放在 /tmp/src 目录下。
如果要修改源代码放置目录，可以指定 io.openshift.s2i.destination label 或者在命令行增加 --destination 参数。
这里的当前目录 ./ 表示的是 openshift/base-centos7 的工作目录，即 /opt/app-root/src。

5. 定义 s2i/bin/run
内容如下：
#!/bin/bash -e
#
# S2I run script for the 'lighttpd-centos7' image.
# The run script executes the server that runs your application.
#
# For more information see the documentation:
#  https://github.com/openshift/source-to-image/blob/master/docs/builder_image.md
#

exec lighttpd -D -f /opt/app-root/etc/lighttpd.conf

6. 定义 s2i/bin/usage
内容如下：
#!/bin/bash -e

cat <<EOF
This is the lighttpd-centos7 S2I image:
To use it, install S2I: https://github.com/openshift/source-to-image

Sample invocation:

s2i build https://github.com/soltysh/sti-lighttpd.git --context-dir=test/test-app/ lighttpd-centos7 sample-app

You can then run the resulting image via:
docker run -p 8080:8080 sample-app
EOF

7. 创建 etc/lighttpd.conf，Dockerfile 中要复制此文件
内容如下：
# directory where the documents will be served from
server.document-root = "/opt/app-root/src"

# port the server listens on
server.port = 8080

# default file if none is provided in the URL
index-file.names = ( "index.html" )

# configure specific mimetypes, otherwise application/octet-stream will be used for every file
mimetype.assign = (
  ".html" => "text/html",
  ".txt" => "text/plain",
  ".jpg" => "image/jpeg",
  ".png" => "image/png"
)
说明：这是一个很简单的 lighttpd 配置文件，配置了如下信息：
（1）服务内容路径：/opt/app-root/src
（2）监听端口：8080
（3）默认欢迎文件：index.html
（4）支持的 mimetype 映射类型

8. 定义 test/test-app/index.html
内容如下：

<!doctype html>
<html>
    <head>
        <title>test-app</title>
    </head>
    <body>
        <h1>Hello from lighttpd served index.html!</h1>
    </body>
</html>

9. 为了能够安装 lighttpd，下载 CentOS7 repo
wget http://mirrors.163.com/.help/CentOS7-Base-163.repo

10. 构建 lighttpd builder image
make build
或者
docker build -t lighttpd-centos7 .

11. 使用 lighttpd builder image 构建应用镜像
s2i build test/test-app/ lighttpd-centos7 sample-app

12. 启动应用镜像
docker run -p 8080:8080 sample-app

访问 http://localhost:8080，显示 Hello from lighttpd served index.html!

至此，说明 lighttpd builder image 构建成功！


参考文献：
1. https://blog.openshift.com/create-s2i-builder-image/