一、问题描述
最近在使用docker部署spring Cloud微服务项目的时候发现，每个服务构建出的镜像文件高达700M。
镜像较大的镜像往往会导致移植，迁移缓慢。最后启动并进入容器发现，jdk用的是openjdk，那么我们就需要在构建镜像时使用更小的jdk作为基础镜像，进而减小镜像的大小.
二、解决方案
使用Oracle的JRE而不是openjdk，并构建成Docker镜像。
2.1 下载并上传jre到linux服务器
jre8下载地址:https://www.java.com/en/download/manual.jsp
jre linux x64
大小大概是80M
2.2 删除无用文件
解压压缩包
$ tar -zxv -f jre-8u181-linux-x64.tar.gz
删除无用的文件
$ cd jre1.8.0_181/
$ rm -rf COPYRIGHT LICENSE README release THIRDPARTYLICENSEREADME-JAVAFX.txt THIRDPARTYLICENSEREADME.txt Welcome.html
$ rm -rf lib/plugin.jar
lib/ext/jfxrt.jar
bin/javaws
lib/javaws.jar
lib/desktop
plugin
lib/deploy*
lib/*javafx*
lib/*jfx*
lib/amd64/libdecora_sse.so
lib/amd64/libprism_*.so
lib/amd64/libfxplugins.so
lib/amd64/libglass.so
lib/amd64/libgstreamer-lite.so
lib/amd64/libjavafx*.so
lib/amd64/libjfx*.so
重新打包
$ tar zcvf jre1.8.0_231.tar.gz *
2.3 新建Dockerfile
vim Dockerfile_jre1.8.0_231
# using alpine-glibc instead of alpine is mainly because JDK relies on glibc
FROM docker.io/jeanblanchard/alpine-glibc:latest
# author
MAINTAINER sandu <1103324414@qq.com>
# date zone 设置时间，避免相差8个小时
RUN ln -sf /usr/share/zoneinfo/Asia/Shanghai /etc/localtime
RUN echo "Asia/Shanghai" > /etc/timezone
# A streamlined jre
ADD jre1.8.0_231.tar.gz /usr/local/java/jdk/
# set env
ENV JAVA_HOME /usr/local/java/jdk/
ENV PATH ${PATH}:${JAVA_HOME}/bin
# run container with base path:/opt
WORKDIR /opt
2.4 构建docker镜像
docker build -t 192.168.75.12/library/jre:1.8 -f Dockerfile_jre1.8.0_231 .
这样构建的jdk镜像大概是130M左右。
2.5 测试
# docker run -it 192.168.75.12/library/jre:1.8
/opt # java -version
java version "1.8.0_231"
Java(TM) SE Runtime Environment (build 1.8.0_231-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.231-b11, mixed mode)
/opt # date
Tue Oct 29 10:22:33 UTC 2019
2.6 推送到Harbor仓库
[root@bogon jre1.8.0_231]# docker login http://192.168.75.12
Authenticating with existing credentials...
WARNING! Your password will be stored unencrypted in /root/.docker/config.json.
Configure a credential helper to remove this warning. See
https://docs.docker.com/engine/reference/commandline/login/#credentials-store
Login Succeeded
[root@bogon jre1.8.0_231]# docker push 192.168.75.12/library/jre:1.8
The push refers to repository [192.168.75.12/library/jre]
0c64e8821df0: Pushed
cc24d9491ad4: Pushed
fd414845c3cc: Pushed
6dbecb8e1a3e: Layer already exists
77cae8ab23bf: Layer already exists
1.8: digest: sha256:3484a7852d1330867c14805c03db28ccde2cc327e2ceb5658aaeb0bea010122a size: 1365
20200618下载的最新版本是1.8.251
不过构建docker镜像的时候需要做些调整，不然容器内时间会差8个小时
/usr/local/src/jre1.8.0_251 # cp /etc/localtime .
/usr/local/src/jre1.8.0_251 # touch timezone
/usr/local/src/jre1.8.0_251 # echo "Asia/Shanghai" >> timezone
/usr/local/src/jre1.8.0_251 # ll
总用量 43M
drwxr-xr-x 2 10143 10143 208 6月 18 10:53 bin
-rw-r--r-- 1 root root 268 6月 18 11:36 Dockerfile_jre1.8.0_251
-rw-r--r-- 1 root root 43M 6月 18 10:54 jre1.8.0_251.tar.gz
drwxr-xr-x 13 10143 10143 4.0K 6月 18 10:53 lib
-rw-r--r-- 1 root root 556 6月 18 11:41 localtime
drwxr-xr-x 4 10143 10143 47 3月 12 14:33 man
-rw-r--r-- 1 root root 14 6月 18 11:44 timezone
/usr/local/src/jre1.8.0_251 # cat Dockerfile_jre1.8.0_251
FROM docker.io/jeanblanchard/alpine-glibc:latest
MAINTAINER sandu <1103324414@qq.com>
COPY localtime /etc/localtime
COPY timezone /etc/timezone
ADD jre1.8.0_251.tar.gz /usr/local/java/jdk/
ENV JAVA_HOME /usr/local/java/jdk/
ENV PATH ${PATH}:${JAVA_HOME}/bin
/usr/local/src/jre1.8.0_251 # docker build -t idocker.io/jre:1.8.251 -f Dockerfile_jre1.8.0_251 .
Sending build context to Docker daemon 161.1MB
Step 1/7 : FROM docker.io/jeanblanchard/alpine-glibc:latest
---> b18af330677b
Step 2/7 : MAINTAINER sandu <1103324414@qq.com>
---> Using cache
---> 032d2550e70a
Step 3/7 : COPY localtime /etc/localtime
---> 11bfcd12b1cd
Step 4/7 : COPY timezone /etc/timezone
---> f04d04a9a714
Step 5/7 : ADD jre1.8.0_251.tar.gz /usr/local/java/jdk/
---> 0bcb7f049c6d
Step 6/7 : ENV JAVA_HOME /usr/local/java/jdk/
---> Running in e986b48fb724
Removing intermediate container e986b48fb724
---> 193adeb5015b
Step 7/7 : ENV PATH ${PATH}:${JAVA_HOME}/bin
---> Running in 4b7fda4a59ad
Removing intermediate container 4b7fda4a59ad
---> bbba3f4d1958
Successfully built bbba3f4d1958
Successfully tagged idocker.io/jre:1.8.251
/usr/local/src/jre1.8.0_251 # docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
idocker.io/jre 1.8.251 bbba3f4d1958 5 seconds ago 133MB
redis latest 235592615444 7 days ago 104MB
jeanblanchard/alpine-glibc latest b18af330677b 2 weeks ago 17.3MB
/usr/local/src/jre1.8.0_251 # docker run -it idocker.io/jre:1.8.251
/ # date
Thu Jun 18 11:49:32 CST 2020
/ # java -version
java version "1.8.0_251"
Java(TM) SE Runtime Environment (build 1.8.0_251-b08)
Java HotSpot(TM) 64-Bit Server VM (build 25.251-b08, mixed mode)
/ # exit