如何在没有JAR的情况下为Spring应用程序构建Docker映像

Question

我遵循这些教程为我的Spring应用程序构建Docker映像，它使用Maven作为构建工具。我在Windows10机器上使用boot2docker VM，将我的项目从Bitbucker存储库克隆到VM上。

https://spring.io/guides/gs/spring-boot-docker/

https://www.callicoder.com/spring-boot-docker-example/

我明白说明，但是，我没有建立一个正确的码头形象。这是我试过的东西。

1. 为Dockerfile使用Spotify maven插件。尝试运行./mvnw来构建JAR和Docker映像。但是，我没有在boot2docker中安装Java。因此无法运行Maven包装器./mvnw。
2. 我试图通过Dockerfile构建JAR，该文件基于openjdk:8-JDK-ALPILE映像。我在Dockerfile中添加了RUN ./mvnw package指令。然后运行docker build -t <my_project> .来构建Docker映像。它在运行指令处失败，声称是/bin/sh: mvnw: not found The command '/bin/sh -c mvnw package' returned a non-zero code: 127。

我的Dockerfile，位于mvnw所在的目录中：

MAINTAINER myname

VOLUME /tmp

RUN ./mvnw package

ARG JAR_FILE=target/myproject-0.0.1-SNAPSHOT.jar

COPY ${JAR_FILE} app.jar

ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/app.jar"]

对于1，我需要在Docker引擎所在的操作系统中安装Java。但我认为这不是一个好的实践，因为这降低了便携性。

首先，我不知道如何在Dockerfile中成功地运行./mvnw。其次，我不确定通过Dockerfile构建Spring是否是一个好的实践，因为我没有看到任何“”教程告诉我这样做。

那么，解决我的问题的最佳做法是什么呢？我是码头新来的。非常感谢您的评论和回答！

Answer 1

您可以在构建中直接安装maven并运行编译。通常，这将是一个多阶段的构建，以避免将整个jdk包含在您的推送映像中：

FROM openjdk:8-jdk-alpine as build
RUN apk add --no-cache maven
WORKDIR /java
COPY . /java
RUN mvn package -Dmaven.test.skip=true
EXPOSE 8080
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/java/target/myproject-0.0.1-SNAPSHOT.jar"]

上面是从我过去做过的相同示例中删除的返工版本。您可能需要调整入口点中的文件名，但关键步骤是安装maven并在构建中运行它。

Answer 2

从您的第二个例子中，我认为您误解了Docker如何构建图像。当Docker执行RUN ./mvnw package时，文件mvnw必须存在于正在构建的映像的文件系统中，这意味着在前面的步骤中应该有一个类似于COPY mvnw .的指令--它将把文件从本地文件系统复制到映像中。

在调用./mvnw之前，您可能需要在映像中复制整个项目结构，如@BMitch的响应所示。

此外，正如@BMitch所说，要生成一个小型映像，通常建议使用多阶段构建，其中第一阶段安装每个依赖项，但最终映像只有您的JAR。

您可以尝试如下所示：

# First stage: build fat JAR

# Select base image.
# (The "AS builder" gives a name to the stage that we will need later)
# (I think it's better to use a slim image with Maven already installed instead
#  than ./mvnw. Otherwise you could need to give execution rights to your file
#  with instructions like "RUN chmod +x mvnw".)
FROM maven:3.6.3-openjdk-8-slim AS builder

# Set your preferred working directory
# (This tells the image what the "current" directory is for the rest of the build)
WORKDIR /opt/app

# Copy everything from you current local directory into the working directory of the image
COPY . .

# Compile, test and package
# (-e gives more information in case of errors)
# (I prefer to also run unit tests at this point. This may not be possible if your tests
#  depend on other technologies that you don't whish to install at this point.)
RUN mvn -e clean verify

###

# Second stage: final image containing only WAR files

# The base image for the final result can be as small as Alpine with a JRE
FROM openjdk:8-jre-alpine

# Once again, the current directory as seen by your image
WORKDIR /opt/app

# Get artifacts from the previous stage and copy them to the new image.
# (If you are confident the only JAR in "target/" is your package, you could NOT
#  use the full name of the JAR and instead something like "*.jar", to avoid updating
#  the Dockerfile when the version of your project changes.)
COPY --from=builder /opt/app/target/*.jar ./

# Expose whichever port you use in the Spring application
EXPOSE 8080

# Define the application to run when the Docker container is created.
# Either ENTRYPOINT or CMD.
# (Optionally, you could define a file "entrypoint.sh" that can have a more complex
#  startup logic.)
# (Setting "java.security.egd" when running Spring applications is good for security
#  reasons.)
ENTRYPOINT java -Djava.security.egd=file:/dev/./urandom -jar /opt/app/*.war