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| '''Docker/Workshop/Image/Erstellung''' - Image-building best practices
| | #WEITERLEITUNG [[Docker/Image]] |
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| == Image layering ==
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| Using the docker image history command, you can see the command that was used to create each layer within an image
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| === docker image history ===
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| Use the docker image history command to see the layers in the getting-started image you created
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| docker image history getting-started
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| IMAGE CREATED CREATED BY SIZE COMMENT
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| a78a40cbf866 18 seconds ago /bin/sh -c #(nop) CMD ["node" "src/index.j… 0B
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| f1d1808565d6 19 seconds ago /bin/sh -c yarn install --production 85.4MB
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| a2c054d14948 36 seconds ago /bin/sh -c #(nop) COPY dir:5dc710ad87c789593… 198kB
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| 9577ae713121 37 seconds ago /bin/sh -c #(nop) WORKDIR /app 0B
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| b95baba1cfdb 13 days ago /bin/sh -c #(nop) CMD ["node"] 0B
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| <missing> 13 days ago /bin/sh -c #(nop) ENTRYPOINT ["docker-entry… 0B
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| <missing> 13 days ago /bin/sh -c #(nop) COPY file:238737301d473041… 116B
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| <missing> 13 days ago /bin/sh -c apk add --no-cache --virtual .bui… 5.35MB
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| <missing> 13 days ago /bin/sh -c #(nop) ENV YARN_VERSION=1.21.1 0B
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| <missing> 13 days ago /bin/sh -c addgroup -g 1000 node && addu… 74.3MB
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| <missing> 13 days ago /bin/sh -c #(nop) ENV NODE_VERSION=12.14.1 0B
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| <missing> 13 days ago /bin/sh -c #(nop) CMD ["/bin/sh"] 0B
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| <missing> 13 days ago /bin/sh -c #(nop) ADD file:e69d441d729412d24… 5.59MB
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| Each of the lines represents a layer in the image
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| * The display here shows the base at the bottom with the newest layer at the top
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| * Using this, you can also quickly see the size of each layer, helping diagnose large images
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| You'll notice that several of the lines are truncated
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| * If you add the --no-trunc flag, you'll get the full output
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| docker image history --no-trunc getting-started
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| == Layer caching ==
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| Now that you've seen the layering in action, there's an important lesson to learn to help decrease build times for your container images
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| * Once a layer changes, all downstream layers have to be recreated as well
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| Look at the following Dockerfile you created for the getting started app
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| # syntax=docker/dockerfile:1
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| FROM node:lts-alpine
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| WORKDIR /app
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| COPY .
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| RUN yarn install --production
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| CMD ["node", "src/index.js"]
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| Going back to the image history output, you see that each command in the Dockerfile becomes a new layer in the image
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| * You might remember that when you made a change to the image, the yarn dependencies had to be reinstalled
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| * It doesn't make much sense to ship around the same dependencies every time you build
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| To fix it, you need to restructure your Dockerfile to help support the caching of the dependencies
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| * For Node-based applications, those dependencies are defined in the package.json file
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| * You can copy only that file in first, install the dependencies, and then copy in everything else
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| * Then, you only recreate the yarn dependencies if there was a change to the package.json
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| 1. Update the Dockerfile to copy in the package.json first, install dependencies, and then copy everything else in
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| # syntax=docker/dockerfile:1
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| FROM node:lts-alpine
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| WORKDIR /app
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| COPY package.json yarn.lock ./
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| RUN yarn install --production
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| COPY .
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| CMD ["node", "src/index.js"]
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| • Build a new image using docker build
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| docker build -t getting-started
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| You should see output like the following
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| [+] Building 16.1s (10/10) FINISHED
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| => [internal] load build definition from Dockerfile
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| => => transferring dockerfile: 175B
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| => [internal] load .dockerignore
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| => => transferring context: 2B
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| => [internal] load metadata for docker.io/library/node:lts-alpine
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| => [internal] load build context
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| => => transferring context: 53.37MB
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| => [1/5] FROM docker.io/library/node:lts-alpine
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| => CACHED [2/5] WORKDIR /app
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| => [3/5] COPY package.json yarn.lock ./
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| => [4/5] RUN yarn install --production
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| => [5/5] COPY .
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| => exporting to image
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| => => exporting layers
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| => => writing image sha256:d6f819013566c54c50124ed94d5e66c452325327217f4f04399b45f94e37d25
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| => => naming to docker.io/library/getting-started
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| • Now, make a change to the src/static/index.html file
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| * For example, change the <title> to "The Awesome Todo App"
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| • Build the Docker image now using docker build -t getting-started
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| * again
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| * This time, your output should look a little different
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| 4. [+] Building 1.2s (10/10) FINISHED
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| => [internal] load build definition from Dockerfile
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| => => transferring dockerfile: 37B
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| => [internal] load .dockerignore
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| => => transferring context: 2B
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| => [internal] load metadata for docker.io/library/node:lts-alpine
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| => [internal] load build context
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| => => transferring context: 450.43kB
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| => [1/5] FROM docker.io/library/node:lts-alpine
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| => CACHED [2/5] WORKDIR /app
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| => CACHED [3/5] COPY package.json yarn.lock ./
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| => CACHED [4/5] RUN yarn install --production
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| => [5/5] COPY .
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| => exporting to image
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| => => exporting layers
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| => => writing image sha256:91790c87bcb096a83c2bd4eb512bc8b134c757cda0bdee4038187f98148e2eda
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| => => naming to docker.io/library/getting-started
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| First off, you should notice that the build was much faster
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| * And, you'll see that several steps are using previously cached layers
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| * Pushing and pulling this image and updates to it will be much faster as well
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| == Multi-stage builds ==
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| Multi-stage builds are an incredibly powerful tool to help use multiple stages to create an image
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| * There are several advantages for them
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| • Separate build-time dependencies from runtime dependencies
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| • Reduce overall image size by shipping only what your app needs to run
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| === Maven/Tomcat example ===
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| When building Java-based applications, you need a JDK to compile the source code to Java bytecode
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| * However, that JDK isn't needed in production
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| * Also, you might be using tools like Maven or Gradle to help build the app
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| * Those also aren't needed in your final image
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| * Multi-stage builds help
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| # syntax=docker/dockerfile:1
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| FROM maven AS build
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| WORKDIR /app
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| COPY .
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| RUN mvn package
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| FROM tomcat
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| COPY --from=build /app/target/file.war /usr/local/tomcat/webapps
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| In this example, you use one stage (called build) to perform the actual Java build using Maven
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| * In the second stage (starting at FROM tomcat), you copy in files from the build stage
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| * The final image is only the last stage being created, which can be overridden using the --target flag
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| === React example ===
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| When building React applications, you need a Node environment to compile the JS code (typically JSX), SASS stylesheets, and more into static HTML, JS, and CSS
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| * If you aren't doing server-side rendering, you don't even need a Node environment for your production build
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| You can ship the static resources in a static nginx container
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| # syntax=docker/dockerfile:1
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| FROM node:lts AS build
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| WORKDIR /app
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| COPY package* yarn.lock ./
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| RUN yarn install
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| COPY public ./public
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| COPY src ./src
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| RUN yarn run build
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| FROM nginx:alpine
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| COPY --from=build /app/build /usr/share/nginx/html
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| In the previous Dockerfile example, it uses the node:lts image to perform the build (maximizing layer caching) and then copies the output into an nginx container
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| ; Summary
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| In this section, you learned a few image building best practices, including layer caching and multi-stage builds
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| Related information
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| • Dockerfile reference
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| • Dockerfile best practices
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| ; Next steps
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| In the next section, you'll learn about additional resources you can use to continue learning about containers
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