Create lean Docker images using the Builder Pattern

If you’ve ever used Docker to compile software during development you’ll quickly find that often your images become large. In this talk we’ll discuss how the builder pattern can be used to create leaner images containing only runtime dependencies, and touch on a few Docker best practices.

This talk was given at GoSheffield on 06/12/2018 and is based on blog post about the same - https://medium.com/@kaperys/create-lean-docker-images-using-the-builder-pattern-37fe2b5d97d4.

Transcript

1. Create lean Docker
   images using the Builder
   Pattern
   GoSheffield - December 6th
   

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2. Hello!
   I’m Mike Kaperys. I currently work at U
   Account (@uaccount - uaccount.uk) as Senior
   Software Engineer.
   Developer since 2012. Writing Go since 2016.
   @_kaperys
   kaperys.io
   mike@kaperys.io
   

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3. The problem
   

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4. Vision App
   Small Go web app which submits
   webcam images to AWS’
   Rekognition API.
   kaperys/blog/docker-builder-pattern
   func main() {
   svc := rekognition.New(session.New(&aws.Config{Region:
   r := gin.Default()
   r.StaticFS("/", http.Dir("html"))
   r.POST("/analyse", func(c *gin.Context) {
   var req struct{ Image string }
   if err := json.NewDecoder(c.Request.Body).
   Decode(
   c.AbortWithError
   (http.StatusBadRequest, er
   return
   }
   img, err := base64.StdEncoding.
   DecodeString(req.
   if err != nil {
   c.AbortWithError
   (http.StatusInternalServer
   return
   }
   labels, err := svc.DetectLabels(&rekognition.Det
   if err != nil {
   c.AbortWithError
   (http.StatusInternalServer
   return
   }
   if len(labels.Labels) == 0 {
   c.JSON(http.StatusOK, nil)
   

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5. FROM golang:latest
   ADD . /go/src/github.com/kaperys/blog/docker-builder-pattern
   WORKDIR /go/src/github.com/kaperys/blog/docker-builder-pattern
   RUN go get
   RUN go build -o server .
   ENTRYPOINT [ "./server" ]
   Dockerfile
   

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6. FROM golang:latest
   ADD . /go/src/github.com/kaperys/blog/docker-builder-pattern
   WORKDIR /go/src/github.com/kaperys/blog/docker-builder-pattern
   RUN go get
   RUN go build -o server .
   ENTRYPOINT [ "./server" ]
   Read-only base image
   Writable space
   Read-only layer
   Read-only layer
   Read-only layer
   Read-only layer
   Read-only layer
   container
   

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7. docker build -t vision-app .
   

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8. Why so large?
   The golang:latest image is based from Debian
   9 and contains the latest Go compiler and tooling.
   We’ve added our raw source code and vendored
   code.
   We’re creating unnecessary layers in the final
   image by issuing multiple RUN instructions.
   twitter.com/ashleymcnamara
   

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9. We don’t need this stuff in
   production.
   

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10. Multi-stage builds
    ● Docker 17.05 introduced multi-stage builds.
    ● Multi-stage builds allow for multiple FROM instructions in a single Dockerfile.
    ● Using a multi-stage build enables abstraction of concerns when building images.
    Typically, the two concerns are build-the-thing and run-the-thing.
    ● Each FROM instruction begins a new build stage.
    ● Files can be transferred between build stages using the COPY --from=id> instruction.
    

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11. FROM golang
    COPY ${pwd} /go/src/github.com/kaperys/blog/docker-builder-pattern
    WORKDIR /go/src/github.com/kaperys/blog/docker-builder-pattern
    RUN go get && CGO_ENABLED=0 GOOS=linux go build -o server .
    FROM scratch
    LABEL maintainer="Mike Kaperys "
    COPY --from=0 /go/src/github.com/kaperys/blog/docker-builder-pattern/server /opt/kaperys/vision/server
    COPY --from=0 /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt
    ADD html/ /opt/kaperys/vision/html
    EXPOSE 8080
    WORKDIR /opt/kaperys/vision
    ENTRYPOINT [ "./server" ]
    Dockerfile
    

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12. docker build -t vision-app .
    

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14. 98% reduction
    Our original image was 920MB.
    We’ve been able to reduce this to 18.2MB (our compiled binary is only
    18MB!) by using the builder pattern.
    

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15. Thanks! Questions?
    @_kaperys
    

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