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## `Source to Image`
`Source-to-Image` (`s2i`) 是由`openshift`提供的一套从自动从代码构建到镜像的工具
和流程。
S2I 提供了一套镜像模版来对多种语言和矿建进行构建
### 应用
`s2i` 适用于将已有程序迁移到 docker 镜像。 `s2i`提供了各类的 builder 镜像，可以
针对不同的应用快速的完成构建。用户不再需要在为应用编写 Dockerfile，也不再需要在
构建过程中运行安装依赖程序 `s2i`可以对构建镜像进行版本管理，向控制代码仓库一样控
制 build 环境 `s2i`提供了可以持续流程，可以进行递增的项目编译，从而大大减少构建
时间
### 原理
`s2i`提供了 builder 镜像，提供了完整的编译运行环境。 `s2i`会把代码注入到 builder
镜像中。在 builder 镜像中对源码进行处理，使其可以被运行。
处理脚本：
- assemble 执行 build
- run 运行
- save-artifacts 保存构建供后续使用 optional
- usage 显示使用信息 optional
### 创建 Builder 镜像
为`singlecloud`创建一个镜像
#### 安装`s2i`命令
```shell
curl -sSL https://github.com/zdnscloud/s2i/releases/download/v1.0/s2i.tar.gz | tar zxf - -C /usr/local/bin/ s2i
```
#### 创建`s2i builder`模版
```shell
s2i create s2i-singlecloud sc
# 进入模版目录
cd sc
```
模版中提供了两个命令来处理
- make build 构建 builder 镜像
- make test 测试 builder 镜像
##### 修改 Dockerfile 文件
```Dockerfile
# s2i-singlecloud
FROM golang:1.12.5-alpine3.9
# TODO: Put the maintainer name in the image metadata
# LABEL maintainer="Your Name <your@email.com>"
LABEL maintainer="GSMLG <me@gsmlg.org>"
# TODO: Rename the builder environment variable to inform users about application you provide them
ENV BUILDER_VERSION 1.0
# TODO: Set labels used in OpenShift to describe the builder image
LABEL io.k8s.description="Platform for building singlecloud" \
io.k8s.display-name="singlecloud builder" \
io.openshift.expose-services="80:http" \
io.openshift.s2i.scripts-url=image:///usr/libexec/s2i \
io.openshift.tags="builder,go,node"
USER root
# TODO: Install required packages here:
RUN mkdir -p /go/src/github.com/zdnscloud/singlecloud && apk upate && apk add bash && rm -rf /var/cache/apk/
WORKDIR /go/src/github.com/zdnscloud/singlecloud
# TODO: Copy the S2I scripts to /usr/libexec/s2i, since openshift/base-centos7 image
# sets io.openshift.s2i.scripts-url label that way, or update that label
COPY ./s2i/bin /usr/libexec/s2i
# This default user is created in the openshift/base-centos7 image
#USER 1001
# TODO: Set the default port for applications built using this image
EXPOSE 80
# TODO: Set the default CMD for the image
CMD ["/usr/libexec/s2i/usage"]
```
##### 修改`s2i/bin/assemble`
```bash
#!/bin/bash -e
#
# S2I assemble script for the 's2i-singlecloud-builder' image.
# The 'assemble' script builds your application source so that it is ready to run.
#
# For more information refer to the documentation:
# https://github.com/openshift/source-to-image/blob/master/docs/builder_image.md
#
# If the 's2i-singlecloud' assemble script is executed with the '-h' flag, print the usage.
if [[ "$1" == "-h" ]]; then
exec /usr/libexec/s2i/usage
fi
# Restore artifacts from the previous build (if they exist).
#
if [ "$(ls /tmp/artifacts/ 2>/dev/null)" ]; then
echo "---> Restoring build artifacts..."
mv /tmp/artifacts/. ./
fi
echo "---> Installing application source..."
cp -Rf /tmp/src/. ./
echo "---> Building application from source..."
# TODO: Add build steps for your application, eg npm install, bundle install, pip install, etc.
go build cmd/singlecloud/singlecloud.go
mv singlecloud /go/bin/
```
##### 修改`s2i/bin/run`
```bash
#!/bin/bash -e
#
# S2I run script for the 's2i-singlecloud-builder' 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 /go/bin/singlecloud
```
#### 创建 builder 镜像
```bash
make build
```
#### Build `singlecloud`
```bash
s2i build https://github.com/zdnscloud/singlecloud s2i-singlecloud singlecloud
```
#### 运行`singlecloud`
```bash
docker run -p 8080:80 --rm singlecloud singlecloud -listen :80
```